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...and I've read that for some people the replacement of the TPS works, and for others it doesn't. And I think that in most cases it is not faulty.
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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!
Andy.
P.S. There are also know PCM faults that cause this problem, cured by a PCM software upgrade.
Edited by ALW on 09/05/2008 at 14:26
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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.
thanks again
Phil
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Phil
The PAS pressure switch only raises the idle 100 revs. You're describing an ECU throttle position reading error.
First; check the TPS plug, the engine loom in-line connector and the ECU plug for water ingress and corrosion. [Yes; the ECU one is a pain.]
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The PAS pressure switch only raises the idle 100 revs.
This is definitely not true, it was the only fault on my wife's car and would cause the rev's to rise to 3k quite regularly.
Anyway, glad to hear that this has fixed Phil's problem - glad to be of help and assistance.
Andy.
Edited by alw on 03/06/2008 at 23:01
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Andy
I'm afraid that it is true. The PSP switch is a normally-closed switch which detects pressure in the feed line of the steering rack. I've repaired broken wires on hundreds of them.
It raises the programmed idle speed by 100 revs to compensate for the increased load from the PAS pump - particularly if held on full lock.
If it caused an idle runaway on your car; then it was affecting, or interacting with, another fault - possibly a software or ISCV error.
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"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.
Andy.
Edited by alw on 05/06/2008 at 14:31
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Andy
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.]
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Screwloose,
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.
Regards,
Andy.
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.
Edited by alw on 05/06/2008 at 22:37
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Andy
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.....
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"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 :) )
Thanks again for your invaluable inputs here.
Andy.
Edited by alw on 06/06/2008 at 17:27
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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 ?
Jim
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Sadly Screwloose has disappeared, his last post was in December 2008.
Perhaps he has gone off with Aprillia!! another good poster.
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Hi Screwloose!
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?
Thanks in advance.
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I've found the white connector easily enough. Unplugged it and a load of water fell out of the sleeving, so hoped it might be the cause.
Although I haven't really had a chance to properly dry it out, so I understand it may not be fixed, I hoped the amount of water that came out would have had some effect, but nothing.
Still got the same problem, as described above.
Whilst the car is moving, the revs climb when the clutch is depressed. As the car slows, the revs drop, but only to "just over" 1,000rpm.
Where will I find the other items to check for water?
ECU Connector? and the other connector?
Thanks guys!
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Turtle
What car, year and engine; there are a dozen versions of the 1.3 alone.
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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
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Hi Screwloose,
sorry for the delay in replying, its been a long few days!
The car is exactly as in the thread title - 1.25 Zetec of 1998 vintage.
White connector checked and working. Revs increase if car is in motion and rest down to just over 1,000rpm once car comes to a stop.
I'm going to try the battery dis-connect, but that will lead to me needing to find someone eho can get me a radio code!
Bought the car without one and have never bothered to get the unit out in order to ask the local dealer. Anyone know how I can get a code? (should I start a new thread?!)
I think if the battery dis doesn't work, then I'm onto the speed sensor to see if its damp or has a bad connection? Is this on the rear of the gearbox? Is it accessible from underneath the car?
Thanks again!
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Re-setting the ECU will only clear the learned values - just pull the ECU fuse. [The handbook will tell you which one.]
Also check the engine loom in-line connector for water. Ford moved it around a lot, due to water ingress issues; just follow the injection wiring until you get to a plastic shroud.
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I am thinking of giving this a try on my fiesta 1.25 2000
I have the Ford handbook which lists Fuse 19 ( in the internal fuse box )
decribed as follows
7.5 amp / colour brown, engine management,radio station memory,aux relay
"do you think this is the correct fuse "? thank you
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"Bought the car without one and have never bothered to get the unit out in order to ask the local dealer. Anyone know how I can get a code? (should I start a new thread?!)"
Email me on alweekes at gmail dot com
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Quick Reply
I have a Ford Focus 1.8 Zetec which experienced similar issues.
I found the TPS and drilled the holes slightly larger to allow for extra turning.
The Amount it needs to turn is surprisingly little.
Mines all fixed now... ( fingers crossed)
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Hi graham, Im having the same revving problem. Could I ask which way you moved the tps once you had drilled the holes?
Thank you
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sladey
The TPS bush removal should be done as a last resort once all the other possible causes have been checked.
It's turned backwards.
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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
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sladey
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.
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Hi well, have now changed the tps and tps plug and stiill revs up when clutch pressed alot of the time. Wondered if it could be the throttle cable sticking or stickyness on the throttle butterfly?
Any advice on how to check these would be great?
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sladey
Not the throttle if the revs drop after becoming stationary.
What voltage have you got on the middle TPS pin?
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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 ??????
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And what voltage do you now have on the middle pin?
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I havnttested this yet, could you post up a guide on exactly how to do this. Thanks
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screwloose, any chance you could tell me exactly how to check the middle pin voltage. Im more involved in mechanical stuff at work rather than electrical things.
When checking will I have to pierce the wires to check the voltage or is there another way to access the pins?
Finally, What are the figures it is meant to read?
I know ones a minus, ones 5v constant and what voltage am I looking to get on the middle slider pin?
Thanks
Edited by sladey on 19/09/2008 at 16:51
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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?
Thoughts appreciated.
Jeremy
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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.
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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 !!
Anyway thanks to all for the advice
Mark
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I changed the heater control valve, (1999 Fiesta 1.25 Zetec) and ever since it's been over-revving (2000-3000rpm) in neutral as described above whenever moving.
Checked there weren't any fault codes and there weren't. All sensors seemed to indicate sensible readings connecting to the obd2 port.
Eventually found that one of the vacuum hoses (that run from the back to front of the engine over the top) had come off on the front of the engine, pushed it back on and it's all great again.
Odd that so many items can cause so similar symptoms.
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