I've got a strange cold start problem with my '92 240. I've tried nearly everything I can think of, and am getting really frustrated. I don't want to replace parts *****-nilly, so I've been testing things carefully. I think I find a problem; replace a part, and it doesn't help. Here's the problem. It's hard to start if the engine is cold. When i get it running, it dies when I press the accelerator. It will also die if I don't press the accelerator. The only way to keep it running is to keep on breifly pumping the throttle. After it warms up it runs well. If the temperature is below 60 degrees it wont start no matter how hard I try. The problem started when I replaced the throttle sensor. It had an uneven idle; surge and slow, surge and slow. I replaced the TPS and that fixed the problem, but then the cold start issue began. Now here's the weird part. If I unplug the TPS, it idles very slowly, but it won't die when I open the throttle. Plug the TPS back in, Idle speeds up, then it dies when I try to rev it. When the engine is hot, it runs fine.

A list of parts I've replaced:
TPS
coolant sensor
lift pump
main fuel pump and filter
pressure regulator
plug wires (old ones were sparking)
I even replaced the ECU, the old one wasn't sending the proper signal to the MAF sensor
replaced MAF, but it didn't work, put the old one back in

I get different codes nearly every time I check them. I'm still getting the coolant sensor code even though I replaced it. The sensor has the right resistance, and I've tested the wires back to the computer.
I've tested the idle control valve
Ive inspected the intake hose for leaks.
I'm not getting signal from the O2 sensor, so I'll replace it, but that wouldn't keep the car from starting would it?

I'd appreciate any suggestions you would have. I've run out of ideas. I think there might be an air leak somewhere I just can't find anything.

 

Forgot to add: it doesn't have a cold start injector.

 

Have you checked the functioning of the idle air controller? It is what controls the amount of air to let in at idle to keep a constant RPM around 700. It sounds like it may be sticking. Pull it out and clean it with throttle body cleaner. Test it while it is out. Simply apply 12v across the pins and it should click open or closed (I can't remember if the default state is open or closed).

 

​​​​​yes, I've tested it, it works as far as i can tell. I applied voltage, and it clicked

 

I'd have said Coolant Temp Sensor typical symptoms but since you have changed it... Even so, these days parts, even the OEM ones, could be questionable.
You don't mention tune up items, plugs, cap, rotor? Compression? How many miles on the motor? A low compression may cause this.
If all those check out, I'd look again at the MAFS and that coolant sensor... The MAFS is a tricky thing, acts bizarrely...
I assume the battery is strong, 12.5+ resting?