My 1991 Z28 with the 5.7 has just had the timing reset and everything else looks ok, but it HATES to idle when cold. I have to keep the revs up and nurse her until it goes into 'closed loop'- then it seems to idle fine. It will NOT, under most circumstances, idle when you first fire it up. I do see a sensor right above the starter on the block that does not have a wire going to it- could that be a factor? Thoughts??

 

I would verify the IAC (Idle air control) valve is working right. It may not be able to open your throttle up enough for cold idle. The other thought would be to reset the MAF buy unplugging it, cranking it, shutting down, plugging it back up and running it.

Sensor above the starter is probably the oil pressure sender. Also make sure the timing advance is still hooked up.

Sock distributor?

 

His sig says it's a 91 so he would not have a MAF, it is a speed density system, MAP
Yes check your IAC and you may want check the CTS which is on the front of the intake manifold. Maybe it is sending a hot reading to the ECM and therefore not going to start mode.

Did this problem just start after you changed the timing?