77 911s - 2500rpm @cold start idle 😮

[Gary427]

New owner of 77 911S - Help

Engine operates great, except during cold start.

Starts normally when cold, holds about 1500 rpm for 5 seconds, however quickly goes to 2500 rpm for 60 seconds, then slowly drops back to 1000 rpm! I don't like a cold engine spinning up to 2500 rpm on start!

Wonder if the "warm up regulator" (WUR) could be the culprit?

[Schulisco]

I expect several issues.
The problem is on a CIS - you can "tune" it in many ways. That means - despite some issues you can make it run still somehow anytime to hide the issues. This may also the case on your car.

To work these issues you need to do several checks. Because every part of the CIS works mechanical/electrical on his own without the supervision of a ECU you need to check almost everthing. But here the sequence is key to the solution.
1. How many turns do you need to close the idle screw? (treturn to previous setting afterwards)
2. Check the fuel pressures (system and control pressure of WUR) and make sure they're in spec with the original settings
3. Check for correct sensor plate height
4. Check the auxiliary air regulator for correct function

Thomas

[EC900]

Having a 77-2.7L also, heres a very handy reference to bookmark…..

https://cis911primer.com/pages/test_troubleshoot.html