George993

Hi, the engine has been rebuilt recently and the car runs very well, starts easily, has very steady idle when cold, but after it warms up at idle it stumbles every few seconds, almost dies, picks up again with higher rpm, stabilizes and repeats stumble... The mechanic who rebuilt the engine noted to previous owner that airbox may need replacement, but I have no additional info about why and if those symptoms were present at the time when the comment was made.

Any ideas how to cure this hot idle? thanks!

Mike Murphy

Sounds like it's running rich. An ideal stoichiometric setup at 14.7:1 (air:fuel ratio) will sputter and backfire and run poorly when the engine is cold. That's what the choke was for on older, carburetted engines.

I don't know much about the CIS injection systems on these cars, but there are plenty who do.

Brett San Diego

Have you ever had the mixture set properly by a mechanic with an exhaust gas analyzer who knows CIS engines? That's a good place to start. It's not that much to have done. I paid $90 for timing and mixture adjustment at a Porsche independent specialist.

Brett

IslandmanPA

If the previous owner was advised to replace the airbox, there is a problem! IF cracked it may be causing an air leak! Suggest you get it to a mechanic familiar with CIS! Air leaks on these systems will cause what you described. Start here: http://members.rennlist.com/jimwms/CIS/CIShome.html

George993

Thanks, this CIShome link looks very useful! But a visit to a mechanic may be needed anyway...