Engine surge and rough idle

[Brozee]

Starting yesterday I started to encounter a slight engine surge. I check the engine day just to make sure nothing was disconnected make sure that all of the sensors especially the MAF sensor was all connected and wired correctly. It was. Driving the car this morning the check engine light came on. What I am experiencing is after I accelerate the car and just let off the gas the car will stutter and I will feel a surge at around 1- 1.33 thousand RPMs, almost in a rocking type motion. Any help or advice on what is that good because in this maybe a idle control valve either way would help greatly thank you. Attached is a video of the problem I'm experiencing. http://www.youtube.com/watch?v=ko19s...e_gdata_player

[Mister Bally]

I imagine you have checked the fault codes by now. Whenever I've had an Idle stabilizer Valve go bad on a VW or Audi engine; the idle varied by800-1000 RPM's although this was on 4 & 5 cylinder engines with one ISV.

[Brozee]

Well I don't have a vag-com and not sure if a normal reader can read the engine codes, I'm sure it can. It could possibly be the large hose that is north of the MAF sensor, might be slightly disconnected on the back of the engine, as I can somewhat hear a sucking noise from air. Will check that out when I get some time.

[MP4.2+6.0]

Would be the obvious--and cheap--place to start. You mention the main intake tubing/clamps in the first reply, so of course check that for starters.

Look over all the vacuum tubing, from my C5 (A6) 4.2 experience especially. Often the small (3mm) tubing. If they are still using the cloth covered (junk) tubing on the 4.2's like they were in 2000 to give it that VW Germanic look, head to the nearest NAPA store and buy 10-15 feet of quality tubing off of a reel. My C5 experience is it started failing in warranty and then continued until I replaced every last bit of it. Particularly any of the lines under any center intake manifold cover and behind the motor; they get really heat soaked, brittle and then crack. The most problematic ones from my C5 4.2 have been under the center cover that goes to some kind of switched valve, and another two that drop down in the back of the motor and relate to the air injection system. That system overlaps w/ cold idle so could fit your symptoms. Typically these vacuum hose failures did generate a bit of engine vibration on my A6, and indeed then the CEL. Since I did the NAPA quality hose change over, end of subsequent similar problems on my C5 4.2.

[K9COP]

... can chain guides? Also, i had similar symptoms on an old Volvo 760 Turbo years ago, turned out to be air flow meter. Just a thought...
K9

[Brozee]

Is it possible to use a standard car scanner to pull the CEL code? My friend has one that I could use. I dont think I need the vag-com in order to pull it do I?

[MP4.2+6.0]

vacuum is pretty obvious, parts are really cheap and you say you thought you heard some air leaking.

Check it the old way in 10% of the time it will take to figure out codes. Just a thought.

[FlyTyinFool]

Originally Posted by Brozee

Is it possible to use a standard car scanner to pull the CEL code?

Yes, any ODBII scanner will read the "industry standard" codes.

I'm really inclined to agree with MP4.2+6.0 about vacuum issues though.

If the "large hose North of the MAF sensor" you are referring to is the main intake to the throttle body, that would also be a possible culprit. The engine would be sucking un-metered air and that would definitely cause a surge.

Otherwise, the Idle Air Speed Motor (the term I'm used to ) would be my next guess. This would be verifiable with an ODBII scanner. I suppose a filthy throttle body with a clogged (or nearly clogged) Minimum Air Passage could go along with this.


Carry on...

[jakematic]

While I can't put my mouse on the exact posts, I've read about this before.

IIRC after checking vacuum and MAF it usualy turned out to be TBA and/or throttle body cleaning fixed it.

Code(s) will probably help narrow it down.

Here is one post I found:
Cold start idle bounce

[Brozee]

Well taking it to my mechanic today. At the dealer right now for a free vehicle service inspection, although I doubt they will even scan the code for me. Greedy bastards. Regardless, I will have it with my mechanic today and he will poke around and see what he can come up with. I checked all the hoses I could get to, and didn't see anything out of the ordinary. On my way to the dealership the car actually turned off while driving it, had to pull over and restart it to continue. Will keep you guys posted on what it comes out to be.