audijim113

I've seen a lot more technical questions answered by a lot of guys. I've also thrown my 2 cents in for a few. However, my post a couple weeks ago has 95 looky loos and no comments. Maybe I didn't describe it right.

By "engine surging" I mean:

2000 A8 w/ 222,000 miles

In the last month or two, on cold start up, the engine revs up a bit, slows down, runs a little rough, then revs up again. (It repeats this 3 or 4 times and everything is fine from this point on. Once it settles down, it runs good, gets good MPG, no hesitation no problem.

It was time for an oil change and I generally have the shop do it, (too old, too fat). However, I thought maybe the filter or MAF might be causing the surge. So I cleaned and oil the KN filter when doing the oil myself. Since I had to wait for the filer to dry, I pulled MAF and cleaned it with MAF spray. I wanted to soak it in a bag of Isopropal alcohol but couldn't get the dam security torx out. (I'm missing one of my security torx bits and it happens to be this one.).

None-the-less, cleaned, oiled filter, cleaned MAF and today on cold start up, it does the same thing revving up, etc.

Now, I'm thinking maybe it has something to do with cold start idle control which keeps RPMs up until it warms up and idle drops. However, I'm not sure what does this.


When doin

icrashcars

obvious question first, did you use vag com to pull any fault codes?

I had a similar issue on my Mk4 VW and it was the SAI pump. You will get a code if this is bad, but you may not get a CEL.

123quattro

First. Don't run a K&N. They aren't very good as an air filter and are very good at killing the MAF. MAFs on these engines don't last that long as it is anyway. Pull the MAF connector and see if it runs better. If so, that's your problem.

2001 S8

Debatable. More of a personal preference.


Good advice. These MAF seem to be touchy.

Good luck.

silverd2

Myth, with nothing to back it.

K&N's do NOT destroy MAF's...the larger micro-particles they may allow through have no effect on engine parts or the MAF...the engine will eat up and burn much larger particles which pass right on through or are burned.

The oil in a K&N filter does NOT pass through and collect on the MAF, unless a real idiot over-oiled it.

I have run exclusively K&N's on every car I've owned with NO effects whatever, other than increased air flow and lower maintenance. My current D2 has run a K&N for 100K miles...no ill effects and perfect original MAF.

The K&N argument is getting really old and has NO evidence to back any claim except that it allows a much greater air flow than paper...and allows larger micro particles in, which do NO documented damage.

audijim113

Thanks D2 for the sane advice on the K&N. For the others who didn't bother to read my post and made suggestions, The CEL light was NOT on. There were no codes.

I posted symptoms and hoped to get a reply. I had no indication it was (or is) the MAF but wanted to rule it out. I haven't cleaned the K&N in a year or so. Note, I cleaned the filter AFTER I noticed the symptoms.

So starting over. No CEL, No Codes, No problem driving, no rough idle. The only problem is the engine revs up a bit more than I like on a cold start, goes down, then back up, repeats several times and runs fine after a minute.



I also cleaned the MAF AFTER the symptoms.

As for unplugging the MAF to see if it runs better, that is impossible, because 1 minute after a cold start, it does run better. I do get good gas mpg. So, wh

silverd2

Sorry, Jim... I thought by now that someone more experienced with this would reply.

I've had little experience with this specific problem (not on a D2 anyway), but all such discussion and symptoms in better forums than this seem to lead to throttle valve adaptation (recognizing throttle closed position, especially) or a dirty throttle plate that doesn't close exactly the same way each time.

If it was mine, I'd start by giving the throttle plate ("butterfly") a good inspection and clean...and then a "simple" adaptation.

The adaptation has to be done by the car (ECM) itself every time the battery or ECM are disconnected >>

After power interruption, turn the key to ignition (DO NOT START YET) WITHOUT touching the throttle...leave the key in that position at least SIX seconds...then start the car. If all is OK, the ECM has re-learned closed position and the throttle valve has been adapted.

Or if you have VagCom >>

" By selecting "Basic Setting" (function 04), Display Group 60 with the ignition switched on. " - - Bentley

On a past Passat, the power was disconnected while the engine was running (battery cell went at idle). From that point on, huge surging while cold and calmed down a bit (but still surged at idle and low rpm driving)...had to be re-adapted with VagCom .

Cheers,
Sam

twentysevenlitres

I would concur with a dirty throttle plate and adaption.
The usual sane advice from Sam...

Experienced a similar problem with the missus' Ford Falcon DBW throttlebody. As they have no idle bypass or ICV on these types of throttlebodies, they rely on minute movements of the throttle plate with tight tolerances at idle. Dirt buildup is enough to upset the airflow out of tolerance.

BrianC72gt

+1...The 40v engine does not have a separate idle control circuit or IAC valve. The throttle by wire relies on opening the main (only) throttle plate SLIGHTLY to control idle.

I wonder if a funky sensor like IAT or a coolant sensor is causing your issue. If you have VAG com, you can log the various sensor inputs on cold start. What sensors does the engine rely upon while in open loop operation? I'm assuming the cold engine is running off a predetermined fixed map until it gets hot enough to safely rely on the O2 sensors and switch to closed loop operation.