t0adman2.8

Hey all. My 12V recently started to idle strangely - surges and dips - which results in a stall when I try to give it gas and engage the clutch. After such an event, the car won't start for five or six cranks and/or a waiting interval. It will finally fire up again and run relatively well until the next episode. Now the episodes are much closer together and I've dropped it off at my shop. I'd like to get some feedback from this learned group so I can share it with my mechanic and deside the best course of action. It hasn't thrown a CEL yet.

What is/are the most likely reason this is happening?

Ausfahrt

You described my car's behavior of a few months ago to a T. It threw a CEL saying the engine coolant temp sensor was giving wack readings. I cleared the CEL and it would stay away for a couple weeks but the behavior would continue. Since i replaced the unit she runs like a champ. Couldn't say if your problem stems from the same place but hope this helps.

PITFALL: when researching the 12V forums and or 12V pages for info on you temp sensor, you may find reference to two separate sensors, one for the temp gauge in the cluster, and one for communicating with the ECU. My A4 has only one sensor (G62) which is a multi sensor found on the opposite side of where the diagram on 12v.org shows it.

JWG

If you have not modded any electrical components, then look at your oem components:

I would put a small bet on your MAF sensor. Have you possibly damaged it while cleaning it? Have you gotten the connector wet with water or some cleaning solvent while cleaning the engine bay?

It could be a lot of things.

t0adman2.8

Havne't done any electrical mods aside from installing oem HID headlamps from an S4. That was a couple years ago. It's possible some water got on the MAF connection. I'll have them check that. No MAF cleaning. Any chance it could be the idle control valve, the fuel filter or fuel pump?

t0adman2.8

I replaced my temp sensor about 2.5 years ago when it was throwing cels. The sensor alone was also causing the engine to through all kinds of other unrelated cels. Once the sensor was switched it resolved everything. I never had stumbling as a symptom. About 6 months ago I took the car in because it was overheating and they replaced the fan clutch, among other things. Ever since then the engine has run a little over midline on the temp gague. I'm at a loss as to where I should even start looking.

moribundman

The wires that ran from the power output stage to the ignition coil had damaged insulation where you just couldn't see it (the wire ran under the intake manifold). A short caused an ignition coil to grenade. I'm not saying that's your issue, but checking won't hurt. Re-routing the wiring won't hurt either.

Note:

- crack in coil housing (it spewed molten plastic all over the intake manifold)

- frayed wiring where insulation had rubbed through, or rather off, over the years; admire corrosion on wire!

<img src="http://pictureposter.audiworld.com/50038/coil0226.jpg">

TheBeast

I'd bet it is the MAF connection.

t0adman2.8

It's starting to look like the sensor I replaced a few years ago busted again and is causing the trouble. I'll try replacing it and see if it clears up. Thanks for the great advice.