LH 2.2 Turbo Breakerless Warmup Idle Stumble

My 242 has developed a weird idle stumble problem during warm-up where it stumbles really bad. The AFR's swing between 12-20, with the rich condition causing an rpm increase to around 1200 rpm, and the lean out is where the stumble happens, down at 400rpm, then it swings back and does this until the engine has warmed up a little more.

There are no vacuum leaks to my knowledge and the base idle was set correctly. Switching IAC valves and MAFs with known good units, as well as setting a base timing of 17* (breakerless distributor mod and RSI Cam) has it idling well when its fully warmed up or completely cold (starts with zero issues, until the throttle is touched).

Throttle body was set to stock settings, and the idle screw wasn't messed with when it was running fine.

Could this be a bad computer or blasted out head? Unplugging the IAC causes a crappy yet consistent rough idle, with both IAC's. I think one was whatever the stock valve is, and the other is a 501 valve...

New wiring harness, good voltages, etc. I get around 10-12in. of vacuum during cold start, and around 14-16in when it's fully warmed up.

TL;DR: Closed loop to open loop idle issues, runs fine, starts fine, doesn't want to idle consistently on LH 2.2 with Breakerless ignition when the temp needle is below the first marking on the dashboard gauge.

Thanks!

What fuel injectors are you running? And what is the part number on your ECU?

My ‘83 244t with LH2.2/Breakerless ran like garbage with the red Saab 9000 fuel injectors previously installed until I compensated for the different flow rate with a resistor wired in-line with the MAF signal wire. It was impossible trying to fine tune the mixture and get a consistent O2 signal cycle before I did this.

Also, which head is installed on your car? Are any unused injector holes sealed up tight?

My ‘83 has the original head (forget the part number, has large coolant passages) and the PO used these slick machined aluminum plugs to seal the KJet injector holes. Unfortunately these have been a constant source of strange idle running (similar to what you’ve been experiencing) due to poor sealing of the o-rings used. I had to make my own out of turbo oil drain o-rings to get them to seal right.

Also could be a fault relating to the coolant temp sensor.