Well as expected, same symptoms after coolant temp sensor replacement. I knew that wasn’t it as I had back-probed ECU terminals and coolant temp resistance was within spec, but everyone says “coolant temp sensor” so I had to try it. Symptoms are on cold start, it fires right up but after a few seconds it starts running rough and black smoke out exhaust. Rev it a bit for about 10 secs and it smooths out (presumably when O2 sensor is warm enough and it goes into feedback mode). Sometimes when hot/warm start it takes a lot of cranking, but no rich running.
So, I know it is NOT:
ECT (engine coolant temp sensor for ECU) or wiring back to ECU
Earths (have been cleaned and checked)
MAF (have swapped with no difference)
ECU (have swapped with no difference)
Plugs, plug wires, cap, rotor (all swapped with no difference)
Fuel pressure (checked and within spec)
Fuel (car does not have stale fuel)
O2 sensor (new one installed and no difference)
Crank position sensor (new one installed an no difference)
This car DOES have a cold start injector, but I have unplugged the wire connector and no difference.
Only other things I can think of that I haven’t checked or swapped out yet are:
Leaky injectors or bad spray pattern?
Leaky cold start injector?
Poor valve adjustment? Car runs fine once warm.
Blocked catalytic converter (would probably not cause these symptoms?)
Ignition coil
Ignition power stage/amplifier
Any other thoughts?
Guess I will just live with the minor annoyance until I put the turbo engine in and hope it doesn’t do the same thing then?!!??