View Full Version : Subtle idle problem on cold start...

03-24-2011, 09:06 AM
All right, the past couple of weeks I've done the following to my '01 1.8TQ:

1. Replaced the post-cat O2 sensor
2. Replaced the MAF
3. Replaced a broken check valve
4. Replaced a broken dipstick sleeve.

All the related codes that have prompted these repairs have been cleared and haven't returned.

When I first turn the vehicle on in the morning, it idles roughly for a few minutes (not nearly to the point of dying) and the check engine light will blink for a few moments and then turn off again. A few seconds after that the car runs fine for the rest of the day. Any ideas?


03-24-2011, 04:05 PM

03-24-2011, 04:29 PM
Could it be a temporary misfire?

03-24-2011, 08:30 PM
I was thinking it was fuel related somehow ... but sparkplugs might be involved.

03-24-2011, 08:38 PM
It could be fuel related, I'm not saying one of the other, just throwing out ideas. The fact that it's intermittent makes me think leaning away from fuel. I hope someone more knowledgeable about this can chime in

03-24-2011, 08:53 PM
'01 1.8T, eh? Have you had the coil pack recall done yet? I'd start there as it is free. If you leave the misfire codes stored (ie: Don't Clear the Codes), then you will probably get a set of brand new coils for free. I would recommend putting in new spark plugs at the same time, properly gapped. I prefer the NGK copper plugs. You also want to make sure there isn't any oil in the plug holes. If so, you'll need to do a valve cover gasket (and should probably do a cam chain tensioner gasket at the same time).

Does it ever miss under heavy acceleration, or does it happen exclusively on a cold start while idling?

03-25-2011, 07:31 AM
I did all new coils a year ago (the upgraded coils) as well as the valve cover gasket, timing belt (and related parts). It only does it in the morning exclusively. It runs fine throughout the day.

I'd love to get the codes when the CEL is blinking, but it doesn't last long enough to catch it. It blinks for less than a minute before shutting off.

03-25-2011, 06:29 PM
Is there no one amongst the great mechanics on this site who has an answer?


03-28-2011, 05:33 AM
Im having the same issue with my 00 A4, it only stalls/ runs rough in cold starts, but once the AIR PUMP stops sending air, all the sudden it stabilizes back up, and RPS are normal

I too am getting a misfire during this cold start, sometimes I hear backfire too.

Would love to get input on this as well

03-28-2011, 09:47 AM
If it doesn't turn out to be air-pump related from what mikhro said, you might want to check this... in the morning, before starting the engine, turn the key to the on position and use vagcom to check the engine coolant temp, and intake air temp to make sure that they are close to reality. If either one of these sensors is giving a bad reading, it can cause what you describe, without necessarily throwing an error code.

03-28-2011, 10:28 AM
If the CEL was flashing, it has absolutely recorded a fault code for the event, without a doubt. You may not be able to read it with a generic scan tool though, because it is an "intermittent" fault. Most generic scan tools will only read the "hard" faults (CEL ON). Vag-com will read them all, and it will even count the misfires (per cylinder!) LIVE.

You find out which cylinder is having the problem. Then you swap the coils around (just trade 2 of them), and see if the misfires follow the coil pack. If they do, BAM: diagnosis. This is how it is done.