Idle drop/ anti stall?

**Saturn** · 15-12-2010,07:42 PM

Hi all
just started having a odd issue with my passat. I have a 2002 Passat 130 TDI sport with 96000miles.

Found recently when coming to a stop as the car stops the idle momentarily drops from about 800 to 600rpm but quickly recovers. It feels almost like its about to stall but doesn't.

The same can occasionally be felt if say changing from 1st to 2nd gear slowly and at low rpm, as you dip the clutch and rpm drops towards idle, then engine momentarily stutters, but is fine as soon as you engage gear and accelerate.

Runs fine the rest of the time, no odd things through the rest of the rev range.
Changed the wiring loom for injectors about 6 months ago and the car just had its service.

Any ideas?

Am about to run vagcom just to check if there are any faults...if so I'll post shortly.

**phil miller** · 15-12-2010,09:07 PM

not sure if vag com will show up anything, but it could be to do with the dual mass fuel

**martin1810** · 15-12-2010,09:44 PM

Vag-com may well show a faulty clutch or accelerator sensor. If the idle dies it will show up on a measuring block read, even if you don't have a fault code.

**Saturn** · 15-12-2010,10:20 PM

Hi guys,
just run vag-com and its not come up with anything.

Phil: are you talking about a dual mass fuel pump? any ideas how to check it?

Martin1810: Could be that to, but there are no fault codes and I'm not sure which measuring blocks they are on nor what they should read.
If I log data of the idle dieing, do you know how will that help pinpoint the problem?

**martin1810** · 16-12-2010,02:22 PM

DMF is dual mass flywheel.
If you log engine measuring blocks, 123, 345 etc especially when the idle dies, something should show. On a B5 somethings can fail and not give a fault code.

**Saturn** · 16-12-2010,03:07 PM

Ok, I'll give that a go and post the results.
DMF was replaced at the previous serivce along with clutch.

**Saturn** · 16-12-2010,08:39 PM

Righto, have logged what you suggested. This is what I have,

5 marks of where the rpm dropped. The marks are a couple of seconds after the event as I was doing it all myself in the car.

MARK1 - line196: Rpm drops to 777 as I drop into neutral, 840rpm as I stop and then it drops quickly to 798rpm (line 200).

MARK2 @line 292 -line 292 didn't really show up

MARK3 @ line 353 - line 350 is me at a stop, line 351 rpm drops to 798 (again the drop I hear and feel)

MARK4 @ line429 - didn't show up

MARK 5@ line 488 - line 487 rpm dropped again momentarily to 798

zip attached with xcel doc in two different versions .xlsx and .csv

The nominal idle seems to be 819-840rpm, so a drop from 840 to 798 is enough to feel and hear.

Let me know what you think.

**martin1810** · 16-12-2010,10:20 PM

I think the problem is a sticking egr valve. I would dissable the egr to see if it makes a difference. Pull the vacuum pipe off the egr and plug the vacuum pipe. You don't need to plug the bit of pipe going into the egr. Take the big air pipe off, look inside the egr and make sure the egr valve is shut. Now when you drive the egr will not function at all. You may get an engine warning light and a fault code, you may not. If the rev stumble is gone you know you need a new egr.

**Saturn** · 16-12-2010,10:49 PM

Thanks,
Will be a bugger if thats the case, as I put a new egr in 12 months ago!

Will let you know how i get on.

**martin1810** · 17-12-2010,11:22 AM

When I say EGR that doesn't mean it has to be the valve. Blocking it is just a place to start. The vacuum line could be at fault or the vacuum solenoid that controls it or even a bad wire conection to the vacuum solenoid. If blocking the egr is a cure, then you start to look for why the egr is acting odd. A dodgy maf or maf connection can have the same effect. I just think egr is simplest and most likely.