Working on a 1993 Lumina with the 3.1L engine, I've been trying to solve this for a couple of weeks now with no luck, the car runs fine when it is cold, but as soon as it warms up, it starts running very rough - misfiring, black smoke, very strong smell of unburnt fuel, then stalls out. When I try to restart, it just cranks and won't start unless I keep pumping the gas pedal.

The original error codes I was getting were 15 (Coolant temp sensor - low temp), 23 (Manifold Air Temp - low temp), 43 (Knock sensor circuit), and 53 (which i get conflicting info as to whether this is System Overcharge, or EGR valve).

I replaced the Coolant temp sensor (which was cracked, but seemed to work when I heated it up with a torch and measured the resistance) and the thermostat (which was in poor condition and was NOT closing completely) - this made the code 15 go away, but the problem remained.

I replaced the Manifold Air Temp sensor and visually inspected all the wires for it, but it did NOT make the error code 23 go away.

I assume that the 43 error code is a result of too much fuel and subsequent misfiring etc, but haven't done anything else to verify this.

I work with starters and alternators, so I was able to verify that the alternator is NOT overcharging or acting up at all; I would assume the code 53 is something to do with the EGR because there are a number of leaks in the exhaust, I intend to replace it after I can figure out what else is going on.

Any suggestions for what to do next?

well, I'm still working on it with no progress - does the ECM only "kick in" when the engine reaches operating temerature? Could this be a general ECM problem that I am just not understanding, or am I misunderstanding these codes?

I am going to break down and take it in to a local garage if I can't figure anything out in the next couple of days, I was just hoping that I could save a few $$$ by fixing (or even just finding) the problem myself.

Yes, the engine operates in what they call "open loop" until warmed up, meaning it is operating with minimal feedback control, using a pre-planned strategy instead.

Once warmed, the system goes "closed loop" and operation is fully controlled by the ECM.

It does sound like your problem is when it comes out of open loop and starts controlling, something is giving a bogus reading and confusing the ECM.

It's funny that you said the CTS, as I've seen it cause that very same problem. Make sure the wiring to it isn't damaged someplace. Try diconnecting it once in closed loop and see if it changes anything. Move the wiring around while it running, see what happens.

Does yours have a MAP or MAF?

It's funny that you said the CTS, as I've seen it cause that very same problem. Make sure the wiring to it isn't damaged someplace. Try diconnecting it once in closed loop and see if it changes anything. Move the wiring around while it running, see what happens.

Does yours have a MAP or MAF?

I tried disconnecting the CTS, it didnt seem to make a difference, neither did moving the wires around, and the only visual indication that there was a problem with it was that the housing around the plug-in was cracked (I suspect that it had been replaced before - that thing is in a really awkward place).

How can I tell if it is a MAP or MAF sensor? - I believe that it is supposed to have a MAP sensor, but I'm not 100% on that.

I'm not not a mechanic by any means, I work on starters and alternators - for which I'd gladly offer any assistance I can to anyone :)

look in the intake hose between the throttle body and air filter housing. Is there an aluminum housing with a black box attached to it in there? IF there is, then you have a MAF, if it's just a rubber corrigated hose, then you have a MAP.

if it's just a rubber corrigated hose, then you have a MAP

it is the MAP sensor then - is this the infamous "bang it with a screwdriver to see if it works" one?

well, i have ordered a new ECM - it comes in on Monday, wish me luck!

well, i have ordered a new ECM - it comes in on Monday, wish me luck!
the computer took care of the problem - now to tackle that exhaust!!!