pearlwhitesix

My A6 has developed a cold start surge lately, it will start and the RPMs engine will surge up and down for about 10-15 seconds before it finally catches into the cold start cycle and is completely fine after that.

I did a search and found a few threads about the coolant temp sensor, one from another member who replaced his but didn't wasn't clear if it fixed the problem.

The strange thing is it didn't show any signs of this problem throughout the winter, always started perfectly even on the coldest days when it was 10F etc. It seems to have started this issue when winter broke and in the mornings its around 50F.

Once the engine is warm any restarts are completely normal.

I will replace the coolant temp sensor first but wanted to check and see if anyone has any other ideas.

Thanks!

GTA_Driver

Any codes showing up in the ECU?

OGBULLYLOCDAWG

Disconnected the battery or reset any codes recently?

pearlwhitesix

I did a scan, no hard codes or pending codes found. It died twice today when I first started time

pearlwhitesix

Have not disconnected the battery recently

OGBULLYLOCDAWG

If this is your issue, then unfortunately I'll be of no help:

I asked about the surging at cold starts because every time I've disconnected my battery or reset codes my 2.8, the RPMs surge up & down on cold starts if I don't leave the key in the on position for a minute or two.

I don't think that's your issue.

Only post I could find with a resolution on a similar problem (but it's on an A8):
http://www.audiforums.com/forum/audi...bounce-141783/

pearlwhitesix

That's exactly what happened the last time I started it up. The first time it actually stalled.
Since this issue started it would surge up and down but never stall.

hanszuko

Hello,

It happened to me like, you have to remove and clean the throttle.

The edges of the butterfly oil fill and junk you do not let air in idle correctly and opens just a few millimeters.

It is also good to clean the air sensor, this is located in the vacuum tube after the air filter should be cleaned with a spray indicated without touching it.

Greetings from Chile.

pearlwhitesix

I need some help, replaced the coolant temp sensor last night and cleaned the throttle. The idle still drops on a cold start and wants to die.
I let it sit overnight and tried to start it, and it started but the idle dipped and surged wildly.

The issue seems to be related to the ambient air temperature.
This morning it was 65. When it dies and won't start it's usually around 50.

What else can be wrong? I checked for vacuum leaks, found none. I have replaced the brittle braided vacuum lines last year. When the engine is at operating temp it drives flawlessly.

It there a way to log data with a vagcom so I can see exactly what's happening when I try a cold start?

Replace MAF sensor?

GTA_Driver

You can try disconnecting the MAF and then start the car, but from what I understand, MAF readings are ignored on cold starts anyway, and the system works off an ECU map until it goes into closed-loop once the car is warm.

There is a possibility of low fuel pressure, maybe your fuel pump is acting up.