M42 Rough Idle Puzzle, ???

[jthorsland]

Transplanted an older M42 into my '93 318i.  Everything plugged in fine except there was no boss on the block to attach the knock sensor - as a result, I get a 1225 code with the stomp test(knock sensor).  Here is my problem - The car starts up immediately and idles steady for about 15 seconds, then starts idling very rough. If I try to drive the car it exacerbates the problem, no throttle response and idling at 400 rpm. as soon as the coolant temp passes 1/4 on the gauge, the car runs perfectly at all rpm's and idles steadily. I have cleaned the ICV, replaced the coolant temp sensor,checked for vacuum leaks as best I could. I am baffled, could the lack of signal from a knock sensor cause this? Any suggestions would be welcome.

Jay

[318808]

I have some what of a similar issue with my 1997 m44 with a bad rear knock sensor. At start up it idles a little rough as if a slight vacuum leak. I just assumed it was a vacuum leak causing the rough idle but perhaps it is the bad knock sensor. The car does run sluggish if your going up hill as if no power which confirms to me bad knock sensor. I have the new knock sensor but just have not made time to install. I will let you know if it solves my idle issue. Norm