1998 A4 1.8TQA, 95k miles, Not Chipped

CEL pops up a while back and pulled THE CODE, P0304. So, I followed the troubleshooting tips and swapped coils with #4 and still get the 0304. Swapped in a brand new coil and still same code. Replaced all plugs with new and still 0304. Did a compression test on all four cylinders and got (1 to 4: 180-187-192-184). Seems fine with only minor variation between cylinders. So, decided to pull the fuel rail and swap injectors with another cylinder and #4, still get 0304. The only odditity that I notice is that when I first start the car up the boost/vac gauge reads around 16psi VAC @ idle when cold, it pulls more vacuum (19.5psi) as it warms to operating temp. The car pulls fine under boost and only hiccups when cold. Any ideas what it could be? I've got a mental block of where to go next? I've cleaned the TB and IAT and MAF. The ICM (POS) is less than a year old... Any direction would be greatly appreciated!

 

I'd have to go with bad icm.
you can try to test it.....

http://forums.audiworld.com/a4/msgs/1594531.phtml

You seem to have eliminated the other possible causes.

 

I bought a Hueco ICM for a spare last year. I popped it in and it didn't seem to make a difference. But as delicate as they are, it could be bad, too. I'll test the Bosch ICM currently being used. But, I'll drop the Hueco in to see if that helps, first.

Off-hand, do you know if those vac readings seem normal? It seems odd, but I know on cold-start injector cars it is normal, but not sure about the A4. I'll try the ICM swap tomorrow. Thanks for the response!

 

Performed the ICM test and the Bosch one is good and so was the Hueco. I did swap the two on the car, too and there was no change. I hooked up a software diagnostics program and noticed what seems to be unusual, but I'd need someone to confirm/compare to similar A4 model. The ignition timing at idle sticks on 12 degrees BTDC unless I blip the throttle (and then it acts like it should--varying). Is it in a limp mode (this is without the CEL coming on) to stay dead on 12 degrees at idle? Or is Audi that good in keeping everything in harmony? Any other suggestions?

 

Man, what else could cause a misfire in just #4? i am stumped.

You did compression, so that rules out headgasket, replaced coilpack, rules that out, changed plugs, tested ICM?

What else could cause it? At first Im thinking boos leak because of the vac readings, what about the secondary air pump that runs when the car is cold? But why would that cause a misfire?????

Good luck, if you find the cause, please post back, because this is one of those rare things that are hard to figure out, and likely you will help someone out.

 

Do all A4s come with a 2ndary air pump? I don't have one...

I replaced the coolant sensor because it's readings looked funky, but the new one did the same thing (fluctuated the temp readings as it was warming up around 160* F)--no help. The vacuum being low during warmup is due to the throttle being slightly open according to the throttle angle reading (bounces around .8-1.2%), I guess???

So, everyone's (non-chipped) A4 1.8s has a FIXED 12.0* of advance at idle???

 

Can you test the wire going to the coil pack, maybe too much resistance from corrosion?

 

From the ECU to the coil connector? What range should it fall in? For all 3 wires? I know that have continuity when I checked a few weeks back, but I didn't check for resistance values. The implication is that there isn't enough spark energy?