My son has just returned from a couple of days away (including motorway journeys ) and says that on several occasions when pulling up to a road junction and putting engine into neutral, the car revs went up to 5k plus.
He reckons that he`s checked to see if the throttle cable etc was jammed , car mat sticking and anything else obvious but has found nothing .
We`ll be looking at it in the morning in the daylight but in the meantime does anyone have any experience of this problem orhave any suggestions?
I`m hoping to find a sticking mechanical problem somewhere that will be cured with a drop of oil but is there anything electronic that might cause this fault?
Fiesta Zetec Over-revving -
Andrew Moorey (Tune-Up)
Carefully look to check for mechanical fault on the linkage. I suspect though it may be a problem with the throttle position switch voltage having risen above its top parameter when closed. This can be cured by cleaning the throttle butterfly and venturi with some petrol (nothing stronger)on a toothbrush then disconnecting the battery for at least 15 minutes to erase the adaptive memory then reconnecting, start the engine and let it idle for 10 mins until the ECU has learned the 'new' voltage for a closed throttle then go for a run 10-15 miles in varying conditions. Failing this the idle speed control valve can be troublesome.It is usually located onto the inlet plenum under the inlet tracts The ports can be washed clean of sticky tar with some carb cleaner but often replacement is the answer.
Hello, I was getting really annoyed by this problem, and couldn't find anything much useful on the net, so I'm spreading this answer all around :) Hope it helps. This is not the same engine as yours, but the problem might be the same:
I was trying to solve this problem for a couple of days and found what causes it. I have an 1998 fiesta with the 1.3 Endura-e engine (the same is one installed in most KA cars):
- it is caused by the throttle position sensor (tps) - a small black plastic piece with a three-wire plug which is located on the back side of the throttle body.
- in my case it was not faulty because i've taken it out and measured it with an ohm-meter, nor was the connector faulty. I've read that sometimes the connector itself can fail, and that there exsists a revised one.
- it was the wrong resistance of the tps in the idle throttle position that was causing it - it seems that this is a design flaw and that TPS is set to work near the "edge" and over time when the material changes its properties this causes it to go over the ege - and overrev.
The TPS in endura-e is a potentiometer which is connected like this:
- one pin is connected to the minus (chasis)
- the second one is connected to constant 5 volt source from the ECU
- the middle pin is the slider and changes the voltage as the throttle turns. When you turn the key (give a contact) and measure the voltage between it and the chassis in idle, it has to be 0.4 V. In my case it was 0.55 V
You can adjust this sometimes by loosening the screws on the tps and moving it to the side (it has a little play)
What I did (and I don't recommend it is to solder a 5k ohm trimmer pot between the slider (middle pin) and a minus pin (the brown wire in my case) and with it I can regulate the idle voltage from 0 to 0.55 V and by experimenting i could clearly see:
- if I set it above 0.4 V it has a tendency to revv a little longer
- if I set it above 0.48V it is overevving madly
- if it's at 0.4V - its fine
Of course you shouldn't turn the trimmer too low not to short-circuit the ecu source, and if it's set too low the engine might have a tendency to stall at idle. AND NEVER DO THIS if you don't know how to fit it firmly and to insulate it properly.
First try loosening the screws (just a little) with a star screwdriver and tapping the tps so that it moves in the same direction where the throttle turns when increasing the gas. Be careful not to spray the tps with wd 40 because it will make the problem even worse (it affects it a little) and if you're removing it remember to look carefully where the axle sits in it's slot because if you mount it back just a little off it could make it worse.
PS My car is still sometimes stalling when idling, but I think, This is an another problem (with the idle air control valve)
My wife has a 1.25 Zetec Ghia, which suffered this problem and the TPS was fine.
Essentially if the car is out of gear but there is road movement, the engine revs would climb. They would always dip briefly as the clutch was depressed, but then climb again.
Ford diagnosed a faulty ECU (water ingress) and tried to charge me >£600, which I elected not to pay and decided to live with it for a while.
Recently, whilst using the car for work journeys I decided to try and fix this. Some research revealed that the power steering has a pressure switch, which is designed to increase engine revs at low RPM (while parking for example), to prevent the car from stalling due to the power steering pump load.
At the offside front of the car, under the steering rack there is a two-pole connector (white on our fiesta) with two wires that hang down. This is connected to a normally closed set of contacts in the pressure switch - as the steering is turned this switch goes open and the rev's climb. If the wiring fails to this switch (and it's very exposed down there) the PCM thinks the switch is operating constantly and hence increases engine RPM.
A simple test is to unplug the connector, start the car and short the terminals in the connector with a screwdriver - if the revs don't change, it's probably open circuit wiring. If you pull on the wires you might find one falls out. You can also put a meter in continuity mode (buzzer mode) across the switch contacts and get someone to turn the steering aggressively whilst stationary and engine running, to prove it's working correctly - it should measure a short circuit, going open as the wheel is turned.
If this is the case, just temorarily shorting the wires provides a fix that disables the system, which makes the car more driveable, the lack of engine braking with this fault can be dangerous and I didn't experience any stalling.
Ford were useless when trying to get a connector - I was told I'd have to buy the entire wiring loom for the car!. The connector is a standard automotive type as used on injectors etc. and available from Bosch, AMP, Delphi etc. so some hunting around might get you one - I got one from a Triumph motorbike!
P.S. There are also know PCM faults that cause this problem, cured by a PCM software upgrade.
Thanks Andy - you've just resolved long standing issue with R reg 1.4 Zetec Ghia Fiesta over-revving. My symptons were very slightly different in that the car would over-rev (around 1700 RPM) regardless of whether the car was in or out of gear, with clutch raised or depressed as long as there was road movement. As soon as vehicle became stationary, revs would drop to around 1000 RPM. Unplugging the vehicle speed sensor provided some relief, but I was never comfortable with that (sensor must be there for a good reason), so lived with the issue until now.
"If it caused an idle runaway on your car; then it was affecting, or interacting with, another fault - possibly a software or ISCV error."
I obviously bow to your experience and knowledge here, since repairing this fault has completely cured my wifes car can you elaborate further on the other faults you mention please.
I'm aware of PCM updates relating to over-revving, but ISCV is not an abbreviation I've heard of.
The fact remains though, that in my case, the only thing I've fixed is this fault and the problem has gone away, previous to fixing it, it would over-rev to 2-3K and there was an almost complete absence of engine braking. I accept the design aim may be that the switch only gives a 100RPM rise, but in reality it's obvious to me that it can (for circumstances maybe neither of us fully understand at present) cause RPM rises dramatically higher than this. The posts below seem to be evidence of this too. The RPM rise only occurs in the presence of measured road speed, once stationary the RPM's drop.
Maybe there's another fault I should be fixing too? Any input would be gratefully received, I'm not an automotive engineer, but can do electronics ;)
A side benefit of this is a big improvement in fuel economy too on our Fiesta.
Sorry; these acronyms are getting so common that I forget that they're not universally understood. ISCV = idle speed control valve.
The idle control on these systems is unique. It's an adaptive, learning, measurement of the lowest TPS [throttle position sensor] voltage encountered in that drive-cycle, [the "ratch" voltage] with the addition of a small tolerance, being compared to the current reading from the TPS.
The TPS reading sets the ECU in various throttle position categories; the relevant ones here being the lowest two; "part" and "closed." When the ECU is in "part" throttle mode the ISCV is held fully open; [capable of giving 2-3,000 revs unloaded] when the TPS voltage drops into the tolerance zone, then it changes to "closed" and actuates idle protocols to reduce the ISCV opening to give an enhanced idle if there is still a pulse from the VSS [vehicle speed sensor] or a normal idle if there isn't.
This is it's great weakness; if a low ratch voltage has been set, then the current reading never get low enough to be recognized as "closed" - the ECU still remains in "part" and the ISCV stays wide open. Hence the frantic idle speed, "idle flare" and the "cruise control" effect until long after the vehicle is stationary. The PSP switch should only be able to initiate enhanced idle - the fact that it caused a lot more would indicate that it back-fed interference and confused the ECU [through one of many software holes?] into going back into "part throttle" mode.
Ford have had nightmares with this system. It was introduced to de-skill the setting of a closed throttle switch - no fine adjustment is needed on these TPSs, the ECU learns for itself.... in theory. There have been countless modifications, software updates and service bulletins - but, even now, the dealers still send the occasional one to me for the application of my criminal bodge. [They're not allowed to do it.]
Thanks hugely for the detailed, extremely informative reply. As an electronics engineer this is exactly the kind of information that allows me to understand what's going on and what you have described makes perfect sense.
Given that my wife's car no longer over-revs I'm not concerned, but it is a hugely fascinating insight into the system's operation which could come in useful should the problem re-occur.
The first thing I checked was the TPS, I actually removed it and connected a PSU, observed the wiper output (the TPS is simple a potentiometer with 5V (IIRC) across it the wiper then producing a voltage output proportional to throttle position.
Looking at the wiper output on an oscilloscope showed it to have a smooth voltage sweep with no voltage steps or noise apparent, a common problem in pots (it's the equivalent of a noisy volume control on your amp!).
The software element is most likely a problem, I've long thought that many modern cars have what seems like bugs in the ECU code, things often work well when new, but go awry as unexpected things happen with age that the engineers didn't consider. This will only get worse in my view as increasing complexity, driven by emissions reg's, make systems ever more complex, with ever more sensors, wiring, connectors etc.
What is your background, it seems so hard to find engineers witht he obvious detailed knowledge you have, I expect your skills are in great demand! To have my wife's car diagnosed, by a Ford main dealer, as having a faulty PCM (ECU) when there's nothing wrong with it in my view is a sad indication of how this modern complexity can cost the customer dear.
I've always run used vehicles, but the complexity of new cars scares the hell out of me due to the potential costs that can occur. If only everyone was as knowledgable as yourself.
P.S. you explanation may also explain why after I examind the PCM (disconnecting it completely) the car appeared better for a while, the problem almost disappearing fro a short period (I'd thought this had fixed it at first); I suspect this resets the learnt TPS voltages.
I'm glad you understood it; I've just re-read it and wished that I'd taken more time.
Software on vehicles is de-bugged until it - just - works. Every version is full of holes that, hopefully, get fixed on the next one. There are many hardware versions too; Ford use a four-letter ECU code [SHAY, TUNA etc.] to ID them; but you never know what version of software the car has installed until you plug it in.
The TPS rarely fail; it's more usual that they can't get down to the centre-pin voltage that they registered when cold; in-line joint corrosion and induced noise are only two possibilities. As far as the PSP switch goes; if water had got in and was producing a fast-changing signal, that would likely be beyond the software's ability to cope. It expects yeah-or-nay on that pin; flickering shash would likely make it lose it's marbles.
My "criminal bodge" is to drill-out the TPS bushes and use the slack to achieve the lowest possible signal voltage. The ECU doesn't seem to be able to accept a ratch voltage below 0.8v; so if you can get 0.7v at the TPS - it can't follow it down and gets the message - throttle closed! That little trick has cured hundreds of Fiestas, Ka's and Pumas over the years - many after spending ££hundreds at the dealers - who won't do that "mod."
De-powering the ECU erases all the learned values; it needs 20 miles of varied driving before it hones it's settings somewhere near right and adjusts itself to your style.
You're right about newer cars - particularly common-rail diesels; far too many [cheap] highly-stressed sensors and actuators, all linked by increasingly-fragile cabling. If they go wrong after 4 years you just break them.
As to being in demand; not really. I've lost interest in trying to keep up; the bones are falling apart and, after 35 years in diagnostics, I'd love to get right out of this trade. So if you can think of a use for a technically-minded cripple.....
"As to being in demand; not really. I've lost interest in trying to keep up; the bones are falling apart and, after 35 years in diagnostics, I'd love to get right out of this trade. So if you can think of a use for a technically-minded cripple....."
I think you could make some money running a subscription-based website supplying great technical insight into the foibles of modern cars.
I think it's sad that as engineers we often get disillusioned and don't always feel valued. I for one know that if I was confident of receiving the expertise that you've displayed when I take my car in for service or repair, I'd be more than happy to pay for it. What annoys me is paying top whack (even Ford dealers round here charge 80-90 / hr labour) then not getting the level of expertise and confidence in a swift repair that one should get through a dealer network. I appreciate often diagnosis is an iterative process, but in many cases I've little confidence in ever getting a satisfactory outcome, and long the way it nearly bankrupts me!
I've always used good local independant garages, but finding ones with the expertise required isn't always easy, my old car (ovely, simple Citroen ZX diesel) was well looked after this way, but my new TDCi is so much more complex and the garage I used to use have already demonstrated their lack of experience, so I'm currently back to the dealer networks. My way out is a good warranty to cover the most scary bills (fuel system parts, DMF's etc.).
Give that website idea some thought though, startup costs are low, you can run it in your pyjamas and from a laptop in your garden (maybe not at the same time :) )
Screwloose, do you do a diagnostic service or produce a book ?
Am a teacher trying to earn acrust (long sad story), repairing and selling
motors. The sensor problems seem simple but the cause of the symptoms
often seem obscure.
Can you help ?
You've helped so much on these forums, your knowledge is invaluable!
My wife's car has just started to do exactly this. On Wednesday I drove down some country lanes and encountered some flooded sections. The worst of these the water was about 18 inches deep on the other side of the road and someone was already stranded in that lane with water lapping up the drivers door!!
I took the shallowest route, following everyone else, keeping the revs high and doing all the normal checks once through. I then drove home a further 25 miles with no problem.
The following day, the car shows these symptoms from start up.
Engine revs (races) between gear changes. If the revs are below 2,000rpm at gear change, they stay low.. Over 2,000rpm and it races to 4000rpm until the clutch is raised on the newly selected gear.
It also idles at a little over 1,000rpm, which I believe is a little high?
Sods law says that I was about to sell reliable little car to my niece for her to learn to drive in! She can't have it with this fault!
Where should I be looking for these connectors to check? I've got Haynes and also the Ford Technical CD to help guide me.
If its a case of water ingress and some wiring needs checking out, its a job for me. ECU's scare me and I'll probably need to get it to someone with additional knowledge or equipment?
Hi, I have had the over reving problem with my car for the past year and half, i have spent a lot of money with 4 different garages, even including ford.
I have searched and searched on the internet for a resolve, when i stumbled on a forum with a simple solution,
I wish i had noted the guys name to pass him the credit for making my car run like a DREAM !!!!
SIMPLE SOLUTION : UNPLUG THE BATTERY FOR HALF HOUR
Amazingly as simple as this sounds, we all drive our cars very badly, changing gears late / pulling off when the engine is cold and a whole host of other bad habits,,,,, however with these computerised cars we cant get away with this for long as the computer resets things to the way we drive IE increases the revs.
I dont know all the technical terms, but taking out the battery resets the car and then all you have to do is drive PROPERLY for a few miles and - just like magic problem solved,
well this worked with my car So good luck and i hope this works, its at least worth a try and its by far the easiest and cheepest option
yes I know. Thanks I have a spare tps so was going to experiment, however I have since learned of a ford TSB relating to this issue 025/2002, in which they have devised a modified tps wiring loom connector. If anyone needs more info just quote that tsn number at ford
It's worth a try, but it's never worked for me and, IIRC, wasn't really for the 1.25, just the 1.3. Basically it short-loops the TPS wiring and means that it doesn't go through the engine loom connector block, or pick up so much EMF interference from the coil area.
Watch out for all the loom wires being black - some cars are - that can make the job a bit more interesting.....
When drilling out the TPS bushes; use a fast drill. They'll spin and melt out, leaving a nice big hole. Aim for 0.7 volts max on the centre pin; key-on, throttle shut. Just nip the bolts up.
Say theres traffic. The traffic moves so i accelerate to move up, now when i depress the clutch and stop the revs rise to 1500ish then eventually come down, half the time down to 600ish then bounces back up to 1000 revs ??????
I read through the threads on the Fiesta 'over reving' with interest and have been hunting around for the likely cause of a similar problem with my wife's 2003 Focus 1.6 Petrol.
The car was running absolutely fine until 2 weeks ago a lorry ripped the rear bumper off her parked car and it went in to be repaired. 2 weeks later the car has just been returned and looks great. I went to pick the kids up from school and on return as I dipped the clutch to change down to second and the revs stayed at around 1500 rpm. When I later had the car parked and started the engine and revved it the engine hung at around 1500rpm then after blipping the throttle returned to normal idle.
The only part on the car replaced was the rear bumper and the rear parking sensors.
Has two weeks of the car sitting around meant that the throttle body or idle control valve become gummed up, coincidentally do I now have a problem with the TPS sensor, or could the fitting of new non Ford? sensors result in a voltage problem at the TPS, or ECU thereby causing the problem?
I've recently had the over-revving problem as described al the way through this thread. I have a 1998 fiesta but the revs just keep building until i release the clutch. This can be a pain when coming to junctions.
However, i have taken it to a garage and they have replaced my Idle Control Valve as it was causing part of the problem, and they also replaced the Throttle Potentiometer Switch which was the second part of the problem.
However, if you have a fiesta (below a 1999 reg i believe) then you also need to buy a connecting loom, as they have better terminals. I had all this done and now (fingers crossed) the car is fine.
For a quick fix though, i have read on other threads that by disconnecting the battery for half an hour, it resets the ECU and therefore the revs are apparently reset to low, therefore stopping the high revving problem, although, i have not yet done it myself so not sure if it works.
I know this is an old post, but i thought id chip in.
Id been having this same problem on my W reg 1.4 zetec ghia whith the revs initally going down then climbing to around 1700 then back to 1200 when you come to a junction or a stop. The revs would also climb with the clutch in, if say you were going down an slope etc.
I lived with this for ages then found this site. I first tried the vehicle speed sensor which cured the problem but made the speedo stop working, drank lots of fuel and the steering was heavy. then, as mentioned here, i looked for the power steering sensor, and low and behold it was sitting there with both the wires broken off. When i removed the connector one of the wires fell out its postion, so i soldered the wires back on to the sensor directly, and its almost perfect for the first time in 18 months.
The only slight clitch is that the revs die down to 600 rpm for a bit, if im stationary and move the steering wheel, but it hasnt cut out as yet, maybe im just not used to it after all this time !!
Thanks to all the above for helping to solve my problem. 1999 Zetec 1.25 over revving & pulling my daughter along the road. I have had various people look the car over & paid for a diagnostic to no avail. However following the thread above I disconnected the battery for 1/2 an hour & this slightly improved things. Then armed with my Haynes manual I went for the power steering sensor & sure enough there was a broken wire. A quick bodge fix later & presto, a perfect running car. THanks very much. I couldn't have done it without you all. Just need to get a spare connector in readiness now.
Please please please can someone help me? Am very very fed up and anxious with my car! The revs stick every now and again but are becoming more and more frequent, the problem seems to occur more when I have driven, turned engine off taken keys out then drive car again - Only sticks when slowing down or stops and I managed to get the revs to decrease by pressing the brake.
The idle control valve and breather hoses have been replaced and the throttle body checked and the local garage cannot see any faults on the diagnostics
Do you think it is worth checking the power steering sensor? Dont really want to disconnect the battery as I have heard that it can play havoc with the electrics - Any help would be much appreciated!
ford fiesta R reg 1.25 over revving -
I have tried many solutions for this over the last couple of years, and still I get over revving on start up. It is alway fixed for a while by resetting the ECU (pulling the fuse for 30 mins).
I have now rewired so that the ECU is fed from the ignition and resets every night.
I have not seen this solution listed before (possibly for the obvious reason that the ECU won't learn the best settings). However the car is used infrequently for short journeys and I just want to be rid of the over revving.
An old thread I know, but I thought I would the solution to my problem !
Firstly - 1998 Fiesta Xetec 1.25 manual.
Having spent over a year elapsed and 20hrs doing diagnostics plus a couple of visits to the garage my over-revving problem is finally cured :-)
The above thread was really useful and the details from Screwloose really helped me understand how the system should work and why it might not be right, but Thanks to all who posted.
In turn I had tested/changed the following none of which made any difference :-
Idle Speed Control Valve
Power Steering Pump Switch
Throttle Position Sensor (including Screwloose's bodge)
Mass Air Flow Sensor
Finally I happened to noticed that the throttle linkage behind the throttle body occasionally 'clicked' and the idle revs dropped by a couple of hundred. The throttle linkage (at the end of the throttle cable) is quite complicated and difficult to see properly as it is behind the throttle body. One part is a rod about 1.5" long, this is held in place by two cylindrical clips, one at each end.
What I discovered was that while the top one was firmly in place, the bottom one was loose and would slide partly off the end of the rod, it could not come completely off but it was enough to foul slightly on the throttle stop occasionally. This prevented the TPS from registering its 'closed' position as described by Screwloose above and hence the intermittent over-revving.
Removing the clip and then replacing it with a tiny piece of rubber (cut from a small o-ring) placed between the clip and the rod prevented the clip sliding off the end.
The Result - PERFECT running and no over-revving for the first time in the longest time !!!
As usual after spending lots of money, the problem was down to a 20p part and as a final irony - the following day the Dealer rang to say our new car had been delivered...
Anyway - Many Thanks to all the contributors here.