Annoying flat spot/hesitation

[nathanj]

I've got an annoying problem with my car and hopefully someone here will be able to help.

The car is an A4 2.5TDi Quattro, late 98 model, 115k. The problem is that at a certain point, as I slowly lift off the accelerator, the power will cut out very quickly.

I've a feeling the problem lies with position of the accelerator rather than engine revs although it could be a combination of the two as it's more noticable at certain rpm. The reverse can happen as I'm accelerating, for example holding it in second around a roundabout.

It's particularly annoying as it's about the point where your foot is resting when cruising at about 80 (on private roads of course!). If I go over a bump and my foot lifts a little, the power dies and I have to put my foot down more, resulting in a power surge as it goes past the same point!

Hopefully that will make sense, because my mechanic didn't really understand. He put it on the computer and didn't get any fault codes. He has put a new MAF sensor on it, which has improved it slightly.

Any ideas?

[kris_lpgcars]

some many things to check maybe the best idea to do so checks
fist- filters: air, fuel, egr, if poss turbo, inlet, intercooler etc
but the best best idea to get system log thru vag tool

[nathanj]

Thanks for the reply.

It's got full service history and it was serviced about two months ago so it's had new filters. It's just sailed through it's MOT with no problems with emissions, suggesting that it's in pretty good health.

When my new laptop arrives I'll do the system log with vag-com.

Next time I'm getting my hands dirty, I'll have a look at the egr (been thinking it might need a clean anyway). Not sure where to start with the turbo and intercooler.

[nathanj]

Well, the problem is still there. I tried to do a scan for error codes with vag-com but it said it couldn't do it because it's the shareware version.

I've run some 10k boost (intake cleaner) through it. I've also disconnected the EGR valve (plugged the vacuum hose). I've got a couple more mpg now but still have the on/off throttle problem!

Anybody got any suggestions?

[mikeya4]

I think it might have something to do with the injection quantity at idle, not sure if im aloud to link to another site but i found this very helpful(mine was jerky with the on/off) http://www.tdiclub.com/TDIFAQ/TDiFAQ-7.html

[amz]

nathan - how much extra mpg did you manage to get after the intake cleaner? Have you managed to resolve your problem? I've got a 115bhp PD Golf and it doesn't feel as quick as when I bought it, and it has reduced mpg too.... used to get 50-55mpg at 80mph on the motorway, but now tend to get 43-47mpg.

[Steve.666]

I've got an annoying problem with my car and hopefully someone here will be able to help.

The car is an A4 2.5TDi Quattro, late 98 model, 115k. The problem is that at a certain point, as I slowly lift off the accelerator, the power will cut out very quickly.

I've a feeling the problem lies with position of the accelerator rather than engine revs although it could be a combination of the two as it's more noticable at certain rpm. The reverse can happen as I'm accelerating, for example holding it in second around a roundabout.

It's particularly annoying as it's about the point where your foot is resting when cruising at about 80 (on private roads of course!). If I go over a bump and my foot lifts a little, the power dies and I have to put my foot down more, resulting in a power surge as it goes past the same point!

Hopefully that will make sense, because my mechanic didn't really understand. He put it on the computer and didn't get any fault codes. He has put a new MAF sensor on it, which has improved it slightly.

Any ideas?

I have the same sort of problem on an A4 Avant 130bhp 1.9TDI 52, when accelerating hard everything is fine but when lightly accelerating say in 2nd at 2000revs acceleation dies momentarily then comes back 2 seconds later, also when feathering the throttle acceleration comes and goes / seems very sluggish ... when this lack of acceleration is happening smoke is appearing out the exhaust ... it looks like white smoke to me .... as i say, if you drive the car hard its great , no smoke ... timing belt was changed 3 weeks ago by good local garage but this problem only started happening yesterday ... the only other difference since the belt change is that you could always hear a slight noise from the turbo through the passenger air vents but since it had the belt change the turbo noise is now a more clear louder fan noise .. (no whining just wind noise) definately different .... if anyone can help it would be most appreciated ... cheers