I have a 94 Z28 A4 car with 112,000 miles that I purchased a few months back. I haven't had much time to mess with it, but I finally got around to it a little while today. The car ran horribly when I got it. I discovered that the CTS and the plug that goes to it were destroyed, so I replaced those and it ran better. Then, I had the ICM tested and it was also bad. Today, I replaced the ICM. Now the car runs great when you start it cold and revs perfectly. When the car enters closed loop, it still idles great and runs smooth. If I bring the revs up slowly it is perfect. The problem is if its at a steady rpm and you crack the throttle, it will backfire through the TB. If you start to bring it up slow and crack it the engine will rev perfectly. My thoughts are O2 sensors, MAF, or ECM. I thought maybe fuel pressure, but it wouldn't make sense for it to only be in closed loop. Anyone got any advice?

 

Did you scan it for codes?

Sent from my LG-LS860 using Tapatalk

 

No I have not. Unfortunately, I don't have anything to scan it.

 

There's free 94/95 scanning software download link in a "sticky" on the "Computer Diagnostics......" forum.

 

If you cant use the software, take it to an autozone.

Sent from my LG-LS860 using Tapatalk

 

It's often difficult to get OBD-1 scanned ar auto parts stores.

 

I cleaned the MAF and it runs yet better. Still, I have this issue. Once the car is up to temp it gets a rattling sound in the top end if you crack the throttle. Almost sounds like detonation. It also runs rough until you rev past this. If I unplug the cts to force it into open loop, it revs smooth, but still makes that rattling sound. Bad coil? It doesn't start until it hits 160 and gets worse all the way up to full operating temp. The intake elbow has a bad spot that might leak a little bit, but I wouldn't suspect that to be temperature related.