1998 BMW 740 Idle Control Valve problem

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When you say cold start, what do you mean? Long crank times, hesitates and then starts, starts and then dies? The P0173 is a fuel trim code that might be there for several reasons. The P0505 idle system control malfunction might be the throttle position sensor either throwing a plausibility fault or in need of adjustment. Get back with me and let me know the answers to the questions about cold start, I'll be here.

By cold starts I mean the car has been sitting all night, so the first start of the day is very rough. No hesitation nor long crank times, the car fires right up just runs rough. Once the car has warmed up it runs fine from that time on. I'm puzzled, you say the throttle position sensor can be adjusted and I didn't think it could be adjusted. The TPS was replaced less then 6 months ago. Thanks for your reply.

The TPS is fixed, yes, but there is an adjustment for the throttle plate, and it can adversely affect the idle quality. As to the rough idle on cold start, start with the basics(state of tune, leaky injectors?, intake manifold leaks, worn spark plugs) and maybe try some injector cleaner.