Getting a bit of rough idle....

[lswing]

Showed up last week, every day or so, not all the time, but idle just a bit rough, slight vibration, seems about 50rpm low. Thinking plugs or fuel filter? Might just need a little tune up, air filters are newer, slight air leak somewhere? Been a few weeks since any logs but all else feels good.

[Brav]

Doubt its plugs. fuel filter unlikely. Vac leak..

[lswing]

Thanks, best way to start diagnosing? Also, your jhm rotors good? Might get some here, Ben mentioned some vibration issues maybe?

[vitalian]

When I had a rough idle the air filter assembly was seated incorrectly. I eve ntually got a CEL from it.

[kevin]

best way to start diagnosing?

VagCom:mech:

[Chung]

Like others have said, MAF, MAF seals and vac.

[Brav]

A lot of trial and error to do yourself, unfortunately. If you check my old thread, I show how I made a device to pressurize the system to listen for leaks, but it involves plugging the MAF seats (pulling airbox), and making a plug where the diverter valves are.

Rough idle means its unmetered, which means its somewhere after the MAFs with respect to airflow into the engine. likely a cracked/dry line, bad seal on airbox (was it moved recently for any service?). bad fuel filter would starve you at WOT, but should still run smooth. plugged air filter will decrease flow, but ECU will compensate.

Just pray its not the suction jet pump (brake vacuum booster). Be on the look out for your brakes going hard, if it gets worse. Best thing to do is go take it to a shop with a smoker, and just find it straight away. There are miles of vac hoses on this thing. If you want a look at a lot of the lines, how I made my pressure tester, etc, check out my old thread (I was diagnosing as well)

http://www.rs6.com/showthread.php/23948-Rough-idle?highlight=

[905084]

Not your MAF seals (they couldn't possibly leak enough). Not plugs, no way it's the air filter (that's pre meterd air). Vac...brakes work well when it idles rough or not?

[lswing]

Thanks all! Really minor as mentioned, and not on some days, just started last week, been fine for months. I had the engine out a few months ago:) No codes so far. I've got to go to the shop next month for a small oil leak and brakes, will test the system then. Maybe just a small line cracking with the warm summer heat.

[Hy Octane]

Might be a coilpack going out..

[johnnie27]

Mate chev the maf plug itself if the air box has been on off a bit it's way easy to have the pin locators damaged also check the first 10 cm of wiring on the rhs maf (if looking at the car head on) as mine had the exact issue you talk about a. The clip was damaged as was a small wire in the loom as it has a crazy bend there and can Frey my car is now so so smooth it's almost disappointing

[lswing]

...my car is now so so smooth it's almost disappointing

Ha, good one, just step on the gas then!

Thanks all, will give it a look over, when the car is warmer it happens, odd...

[lswing]

Back to getting some more of the rough idle, been off and on. We did a full smoke test a few months back after the car shutdown on the freeway using cruise accell, all seemed tight.

So I'm perplexed by this....the RPM level stays the same, idle just gets rough, I can feel the engine shudder a little, and it's not consistent.

Now this could be the problem....I've been getting a few codes for months, upper Lamba's intermittent, and I've seen them log random numbers...they control fueling yes, so when at idle and fuel is less it's a bit more sensitive? Everything else feels fine...

F'ing O2's are fairly new all around, why the hell do these fail so often? Although I was running hot with my tune so I may have toasted them a bit....

[4.2Crew]

An intermintant rough idle on my 2001 A6 4.2L normally meant a bad or dirty MAF, or a failing coolant temp sensor... A quick way to test the MAF is to simply umplug the connector... If the symptoms get worse, the MAF is probably ok. If there is no change, it might be suspect. You can also remove and clean the MAF sensor from the housing by using the correct anti-tamper bit---or slot the tamper-proof heads and remove with a straight slot screwdriver. Most auto part stores carry MAF cleaner.

BTW, are you getting a random misfire code?...