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Replaced another bad injector and installed the 320i intake runners. Reset the timing, checked for vacuum leaks. Previously I went through the FAQ for setting the idle and WOT, the AFM, etc. Now the car runs pretty good when warm (still down on power due to low compression, but doesn't run like it has a rev-limiter at 3000 rpm). However, it runs like crap until warm up. Some backfiring, dies if you take your foot off the throttle, etc. All I can think of is air metering during warmup. I have two aux air valves and have tried them both. Operates the same.

Hope to do a leak-down check to see if the low compression is due to valves or rings. Believe it is valves becuase the squirt of oil in the cylinder trick made almost no change in compression. If anyone can think of something I have missed or should try, I would appreciate it.

The aux air valves are adjustable. I have mine wide open at the moment until I can change the two temp sensors near the thermostat housing. The aux air valve allows more air into the system and then closes as the car warms up.

The aux air valve won't affect how it runs, it's just a throttle bypass that affects idle speed. All the air that goes thru it is metered air that has gone past the AFM. Timing is the first thing that comes to mind, fuel pressure is another. Long shot, but possibly the AFM. Check the O2 sensor reading, if it's low that points to a lean condition and gives you a direction to go in. Also what's the AFM bypass adjustment like, the O2 should override it after a short warmup, but if it's too far open it can affect idle running, after all, it is a mixture adjustment.

Here I go again...

Searching the archives will reveal my postings on just this very topic. Please use this function to save those of us who have undertaken the effort to sort our car's problems and post about the outcome time and effort in reposting ad nauseum.

The yellow Bosch booklet L-Jetronic Technical Instruction (Robert Bentley Publishers) ISBN 1-85-226008-4 clearly explains the phases of operation from cold start, warm start, warmup from cold start and operating temperature operations, the devices that control those operations and the theory behind the system engineering. Do yourselves a favor and obtain a copy of this manual to fully digest how your car was designed to operate so you can know where to look to diagnose component or system failures.

In particular, this manual explains the function of the coolant temperature sensor relative to the warmup phase of operation. Not only is this component critical to the integrity of the warmup phase but as I have stated far too often, the component electrical connections to these devices are over thirty years old and out of original specification. Increased resistance through these connectors is sending false signals to the ECU operating on microvoltage. Even more particular is the passenger rear ground point on the intake manifold that our sacred Bosch manual identifies as the ground for the coolant temp. sensor and the ECU and that no other ground connections are to be made to this point. Replace this connector and solder a new one to fresh wire of the harness.

I chased this exact problem you describe for years until I digested this information of engineering design. One day, after replacing this connector, my warmup problem has disappeared for over 15 years.

A M H I K

Or you could search the archives and find the original post(s).

I have the blue bosch engine management book but not the yellow. I'll look into that. Don't know why I didn't think of the temp sensors since I just went through that on my son's 528e. If I can get a break from work I'll get back to it. Thanks for the replies.