Hi, I have a 2003 A4 with a 1.8t engine. It has a misfire when the engine is cold.

If I fire it up, it will sit and burble until it goes into (what I think) is closed loop operation. Then it runs fine as long as you are driving it. There is also not any smoke while it is doing this. Only codes are for the misfire.

To remedy the situation, I have tried the following:
-new plugs
-new coils
-new valve cover gasket

Unplugged MAF and no change there.

Any input that y'all have would be greatly appreciated!

 

Could be a bad coolant temp sensor. My A8 had some weird cold starting issues a while back. Replaced the sensor and fixed the problem. Plus the temp gauge started working properly too. Be sure to get an extra retainer clip because they get brittle (plastic) and break easily when removing them.

 

Thank you for the response. I will have to give that a try. Coolant temp gauge appears to work as intended btw

 

There are two circuits in the sensors from what I can tell. One side runs the gauge, the other feeds info to the ECU. One side may be working fine and the other won't be. In my case, the gauge side was crapped out as I didn't have any problems with cold staring the first several months we had it. Then the other side went out, feeding bad data to the ECU causing it to balk.. I just happened to have my reader connected to it observing the coolant temp data while driving down the road. It was showing 190-something and then all of sudden it would drop to like 70F for a few seconds, and then shoot back up. Even with air in the system (which was not the case), it would never read 70F.

 

Well I changed the coolant temp sensor but there is no change.

I took it to an independent mechanic and he could not find anything wrong with it either. Although, he did say that there is a TSB from Audi to fix cold start issues.

Has anyone had your car updated according to TSB 20425 and had success with this issue?

Here is the description of the TSB:

Sporadically after cold start, engine may run slightly rough for a few seconds and the malfunction indicator lamp may illuminate with only misfire diagnostic trouble codes (dtc) (p0300, p0301, p0302, p0303, p0304) stored in dtc memory.