VW Passat Lurching!!!!! - VWDan
Hi All,

At last a tech forum that has people who reply and seem to know what they are talking about!

Right, as short as possible here goes.....

My car is running absolutely fine on idle, round town BUT after a few miles on the motorway develops what I can only describe as a lurch, a bit like when you are about to run out of fuel.

Cut an even longer story short....have done full service, ignition system all fine, plugs and leads, filters all done.

Then I discover the Airflow Meter. The way this thing operates makes a lot of sense in the problem I have, air being cut off or too much but only when the throttle is constantly open and after a while?

Does this sound like an Airflow Meter problem to anyone out there? IF so, and I replace it, does the Haynes Book of Lies get it right when they say you have to get the dealer to reset the ecu or will the ecu set itself by it's learning facility.

£160 seems a lot to spend to find that it isn't the problem!

By the way, this started after my MOT when I had the emissions twiddled with so can you just adjust the meter?

Hope this isn't too much, hope someone can help!

Thanks

Dan
VW Passat Lurching!!!!! - Adam Going (Tune-Up)
Hi Dan,

Have to say that this sort of problem is not easy to deal with remotely, without actually experiencing it or being able to test things, but I am sure everyone here will try their best to help.

In the first instance we do need some more information. Year of vehicle, engine capacity, and if possible the engine code (a two or three letter sequence ahead of the engine number, sometimes on the block, sometimes on the cambelt cover).

Also, is the "lurch" a one-off as you go to accelerate from cruise, or after deceleration, or is it a gradual loss of power ?
Does it only happen at one speed, or at any speed ?

Speak again soon I hope. Regards, Adam.
VW Passat Lurching!!!!! - VWDan
Hi Adam

Thanks for the reply!

Here goes.....Year of vehicle os 1989 'G' Plate, 1.8 multipoint fuel injection engine code PB

The lurch is much more than a one off! It's both while accelerating and cruising it does not affect power as such. Happens at all speeds after you have traveled a few miles of motorway, constant throttle rather than on off town driving.

Hope this helps?

Dan
VW Passat Lurching!!!!! - Adam Going (Tune-Up)
Hi again Dan,

Thanks for all the extra info.

In your first post you said HT leads and cap "all OK". This sounds as though it could very well be an HT insulation fault, most likely from the plug caps/shields to the cylinder head, so, have the leads and caps actually been renewed ?

If so, next on my hit list would be the Throttle Position Sensor (TPS). There may be a bad spot on the resistor track which co-incides with your motorway cruising speed. TPS can only really be checked out using an oscilloscope to look for "hash" as output voltage rises and falls.

Once again, you really may be best off getting this professionally investigated rather than taking chances on possibly expensive parts.

HTH, Adam
VW Passat Lurching!!!!! - VWDan
Hi Adam

That's good info and I think you are right. Going to try and find a VW tech locally.

I don't know about you but I never trust dealers you always seem to come away with a rather large bill!!!!!!

Thanks again

Dan
VW Passat Lurching!!!!! - shaun
A VW garage should be able to find the problem by plugging it into to the diagnostic vagcom machine for about £50.
VW Passat Lurching!!!!! - Mole
Haynes vs Haynes
Depending on the year and injection type, I would recommend buying 'Automotive Engine Management and Fuel Injection Systems' by Haynes No.3344. According to this book it is safe to reset the ECU on my Audi by disconnecting it. According to the Haynes manual for the same car, you need to have the ECU reset by a dealer! Hogwash, basically, I have disconnected the ECU many times without problems. The book is refreshingly comprehensive by comparison to a Haynes manual, even telling you which parts can be unplugged while the engine is running (the manual says this will damage the ECU!). Passats are included in the supported vehicle list but you need to post the injection system type so I can check.

Brian
VW Passat Lurching!!!!! - VWDan
Thanks for your reply Brian

Very useful information indeed! It is the Multi Point fuel injection system, 1989 engine code PB Digifant system

Dan
VW Passat Lurching!!!!! - Mark S
These units are affected by damp/moisture. Check your air filter and intake hoses to make sure that you have not drawn in some water. Another check that you can carry out is to disconnect the air mass meter, if the engine runs better, the air mass meter is at fault.
VW Passat Lurching!!!!! - VWDan
Hi Mark

Can you clarify that it is ok to run the car without the airflow meter connected?

For instance, would it hurt it to run it up the motorway and check if I have the problem without the meter connected?

Thanks

Dan
VW Passat Lurching!!!!! - Mark S
Hello Dan, You can run with airflow meter disconnected, you shouldn't need to go far to notice the difference.
VW Passat Lurching!!!!! - Mark S
Dan: Ignore previous posting!! PB engine has different system to the later models I was thinking of. Engine probably won't run with airflow meter disconnected....Sorry for false info.
VW Passat Lurching!!!!! - VWDan
Ok Mark no problem thanks for thinking about it for me.
VW Passat Lurching!!!!! - Robert Fleming
There is a 1.8 PB engine in my GTI. I too have had a 'lurching' experience, which was worse going uphill. I figured it was the lift pump in the fuel tank. Since replacing it, problem has never recurred, but I still wonder whether is was more down to luck than judgment.
VW Passat Lurching!!!!! - Mole
I too had probs with lift pump but on K-Jet equipped car. The book I mentioned covers Digifant for PB engined cars in depth.

Brian
VW Passat Lurching!!!!! - VWDan
Hi Robert

Could you possibly clarify what a lift pump is!

Is it just part of the fuel pump which is fitted in the top of the petrol tank or something else.

Dan
VW Passat Lurching!!!!! - VWDan
Hi All

Just wanted to let you know (if you're in any way interested ;) ) that I have fixed the problem!!!!!

It was the airflow meter where the MOT guy had changed the settings and made everything too lean. Therefore after a while of cruising the flaps within the airbox would flap shut and open because the meter spring couldn't withstand the constant pressure from the airflow into the car.

Opened up the meter, adjusted potentiometer (think that's how you spell it!) adjusted cog and spring and now all fine. Whole car is running much better fr that matter.

If anyone wants anymore info there is a site I found showing adjustment and how to etc.

Feel free to email me.

Thanks again for all your ideas.

Dan
 

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