My 90 C4 starts real hard and takes 3-4 tries, then it seems as though it is running on 6 cylinders. New fuel pump and filter are in. Timing seems good. Where is the IAC located on this beast? What else to check?

 

Your IAC is probably located in a similar place:


Hen was the last time you had a major tuneup?
spark plugs, wire, cap/rotor, etc.

 

Tune up? About 3 years ago. This start problem is worse when it is cold. I live near Chicago, brrrrrrrrrrrrr too much of the time. I the IAC something I should be looking at?

 

I would not go to the IAC for hard starting (hence the name IDLE AIR control valve)
I would believe that the egr valve might be hanging open after it starts, giving you the funny idle, but you need to check the fuel pump relay.
Sometimes this relay's contacts get burned and pitted, and either the pump doesn't run full speed, or it doesn't come on till the oil pressure switch turns on the pump.
Sometimes the gas cap leaks, and there's no tank pressure to help keep a positive inlet pressure to the pump, and it may cavitate for a short while.
For a real long exercise, you might try putting a fuel pressure gauge on the fuel rail, pulling the plug wires one by one and check the wire resistance, and pull the plugs to find out which cylinders are most affected, and see what a new plug does in that hole....
After that, make sure there is sufficient spark energy to completely burn the fuel with a spark tester, and confirm that your engine head ground wires are clean and tight.
On occasion, it may be necessary to remove the negative cable of the battery for about 2 minutes to clear any gremlins running around in the computer, and have it start off with a fresh learning cycle.

 

Just in case this means anything, the fuel pressure is correct, constant and holds over night too.

 

Another set of Multecs going. Before you waste any more time. Please ohm check the injectors cold then hot. They should have 16ohms of resistance. if they are under 10 they are shot. under 12 almost shot. under 5 they are shorted and that could lead to other problems. watch this video it will show you how

 

I got it started, but still 3-4 starts to get her to hum. Drove it a bit and she has plenty of power. Pulling code 23 "speed sensor". What should the MAP sensor wires read on meter, each wire? Getting closer I hope.