Cold Start issue ( only for a second or two)
 

Hey guys,

Here is a rather odd issue. first off its an 85 911. I know i need intake manifold gaskets. ( not too bad, but there is a dead cyl at idle)

Anyway... I start her up cold, it idles at 1000-1200 for about 3 seconds, then slowly dips down to below 500 rpms. and then pops back up. I cleaned out my ICV it is working ok. This only happens once. then i am good!

Any ideas?

Also, I think i am pinging under load at part throttle below 3000k. I am thinking this is due to the intake leak ( thus making that cyl leaner then the others? Although shouldnt the 02 ( recently changed) be keeping constant check at 14.7 AFR in closed loop? ( not too firmilar with old motronic DME's)

Thanks for the help!
Andrew

I don't think you can address a problem like this until you address your other issue. Fix the intake leak first.

Once that is done, determine if you can when some of the sensors were last changed. Have you had the O2 sensor changed? what about cyl head temp? flywheel pos sensor? it is important to validate all these are working.

hope this helps.

Thanks for the advice. The 02 sensor has been changed in the last 8k miles. I have a wideband 02 laying around from another car. I might weld on a bung and see whats going on with the AFR.

Your right... it would make sence to fix other issues first. At least it would narrow down the possibilities.

Andrew

sure, no problem. start with that fix and go from there. this is what my Father told me to do and he is a retired aircraft mechanic. keep us posted on your progress.