Car:

Octavia 1.9 tdi DSG

PD engine, engine code BXE

Mileage 184K

Recent repair work:

New turbo

New camshaft

New flywheel

The car suffers from very lumpy idle. When it’s first started from cold, it idles fine. As the car warms up, the idle begins to get very lumpy. The whole car shakes! When driving, the car feels fine if slightly under powered, but the fault is not noticeable until the car comes to rest and resumes idling.

I suspect that the car is over-fuelling/running rich for 2 reasons. Firstly, the MPG is down by about 10% on what it has previously achieved. I now struggle to average 40 MPG over a whole tank. Secondly, before the fault was present, I measured the amount of fuel consumed when the car was idling. This turned out to be 0.7L/hr. With the car running lumpy, this has increased to 0.82L/hr. Clearly, the car is over-fuelling itself and causing it to run badly.

Although it idles OK when the engine is cold, this may be because the engine requires more fuel when cold anyway and so the fault doesn’t show up at this temp. Not sure. Any ideas would be greatly received, as this is driving me nuts!

Car:

Octavia 1.9 tdi DSG

PD engine, engine code BXE

Mileage 184K

Recent repair work:

New turbo

New camshaft

New flywheel

The car suffers from very lumpy idle. When it’s first started from cold, it idles fine. As the car warms up, the idle begins to get very lumpy. The whole car shakes! When driving, the car feels fine if slightly under powered, but the fault is not noticeable until the car comes to rest and resumes idling.

I suspect that the car is over-fuelling/running rich for 2 reasons. Firstly, the MPG is down by about 10% on what it has previously achieved. I now struggle to average 40 MPG over a whole tank. Secondly, before the fault was present, I measured the amount of fuel consumed when the car was idling. This turned out to be 0.7L/hr. With the car running lumpy, this has increased to 0.82L/hr. Clearly, the car is over-fuelling itself and causing it to run badly.

Although it idles OK when the engine is cold, this may be because the engine requires more fuel when cold anyway and so the fault doesn’t show up at this temp. Not sure. Any ideas would be greatly received, as this is driving me nuts!

Sounds like cam timing not set correctly , take it back to the garage that did the work for you tell them your not happy

Car:

I measured the amount of fuel consumed when the car was idling. This turned out to be 0.7L/hr. With the car running lumpy, this has increased to 0.82L/hr. Clearly, the car is over-fuelling itself and causing it to run badly.

Could it not be the lumpy idle causing the increase consumption rather than the other way around?

Sounds like cam timing not set correctly , take it back to the garage that did the work for you tell them your not happy

The lumpy idle fault predates the new camshaft, so couldn't have been caused by errors during this work. Any other ideas?

Could it not be the lumpy idle causing the increase consumption rather than the other way around?

Could well be. I guess im just assuming that the extra fueling is the cause of the lumpiness rather than a symptom of it.

Was the lumpy idle in evidence before any of this work ?

Was the lumpy idle in evidence before any of this work ?

Yes, it was lumpy before camshaft change and new turbo, so these repairs are irrelevant as far as i can see. The DMF was changed about a year ago due to it developing the usual rattling noise. But car ran fine after this was changed. Only other thing i forgot to mention was that a couple of weeks ago the fault suddenly dissapeared altogether for about 2 days. Car was perfect and then it reappeared. This led me to believe that it cant be a mechanical fault but more like an electrical one. If the timing was out, surely it couldnt behave properly for a couple of days?!

Yes, it was lumpy before camshaft change and new turbo, so these repairs are irrelevant as far as i can see. The DMF was changed about a year ago due to it developing the usual rattling noise. But car ran fine after this was changed. Only other thing i forgot to mention was that a couple of weeks ago the fault suddenly dissapeared altogether for about 2 days. Car was perfect and then it reappeared. This led me to believe that it cant be a mechanical fault but more like an electrical one. If the timing was out, surely it couldnt behave properly for a couple of days?!

I agree this sounds more electrical than mechanical

Temperature sensor?

Googled the problem and main theme on high mileage cars appears to be MAF / EGR related

How do I test EGR operation?

Just plugged a scanner into the car and read the live data. MAF at idle reads between 6-7 g/s and then changes to about 11 g/s. there is no noticeable change in the lumpy idle when this happens. Any ideas? Does this fluctuation sound right?

If I remove the vacuum hose from top of egr with car idling at normal temp, should I feel a vacuum at this pipe?

Tried a friends MAF and it made no difference. Also changed fuel filter just in case but still very lumpy. Might try temp sensor next. Does anyone know where about it is and there just one?

I think there are two - one for the ECU and one for the dash - not sure where they are though. Needs someone with ETKA or ELSA to pop along and point you in the right direction.

It is the ECU one you should check.

FWIW my mate has just got a 58 plate RS4 Estate and the idle was really lumpy on that. He was worried it was the DMF. After having it checked out the cam timing was out (an Audi main dealer did the cambelt LOL) and also some idiot had replaced an injector with a PD140 injector on a PD170. As it was, Audi replaced 3 of the injectors FOC as it was a PD170 and charged him for the fourth. Now it is as smooth as anything.

Worth checking the Fuel Temp Sender. i belive this is actually in the delivery pump. I've no experience of the 1.9 only the 2.0TDi but in by vast and ranging interweb trawls on TDi's I belive this is a common problem and well documented on the Golf MK4 forums search http://uk-mkivs.net for more info.

Also as Andy suggests the coolant sender. Might as well as they are cheap enough and easy enough to replace.

I think there are two - one for the ECU and one for the dash - not sure where they are though. Needs someone with ETKA or ELSA to pop along and point you in the right direction.

It is the ECU one you should check.

FWIW my mate has just got a 58 plate RS4 Estate and the idle was really lumpy on that. He was worried it was the DMF. After having it checked out the cam timing was out (an Audi main dealer did the cambelt LOL) and also some idiot had replaced an injector with a PD140 injector on a PD170. As it was, Audi replaced 3 of the injectors FOC as it was a PD170 and charged him for the fourth. Now it is as smooth as anything.

He should not have been charged anything , tell him to read the vosa thread . SUK refunded the cost of an earlier injector replacement and changed them all FOC

Edited 10 November, 201114 yr by deecee