I have been battling this issue on my 91 240 for nearly a year. Hope someone can help. The problem: Starts great in the winter, but once the weather warms up it will start but run very rough for about 20 seconds, then smooths right out. It has no driveability issues. I have done a full tune up, oxygen sensor, cleaned throttle body, new intake piping, new in tank pump, midship pump works, fuel pressure regulator, fuel filter, flame box/PCV cleaned, fuel pump relay. The problem seems to be more pronounced when the car has been sitting in the sun. The on board diagnosis reads a 2-3-2 but I am starting to think electrical - heat and electricity do not mix. Any ideas? I have researched this to death, but cannot find a probable cause.

 

How about the Coolant Temp. Sensor? It tells the computer how warm things are and to adjust the fuel accordingly...

 

i'm going to throw this out into the mix... if the plugs wires cap rotor are good maybe the power stage is going out slowly...

 

Where and what is the power stage?

Wouldn't it throw a code is the coolant temp is bad?

 

The OBD1 system used on these cars is hit and miss, mainly miss. I use it it because it's there but don't rely on it much. So, no, not necessarily--it should though.

 

the power stage is a ignition amplifier, its between the ICU (ignition control unit) and the ignition coil, acts like a power switch. not all 240's have them, depends on which ignition ssytem they got. if yours has the EZ-116K (which I'm pretty sure all US model 1991 240's have) then, this power module is probably jammed up against the inside of the left fender behind the left headlamp. the plug is almost as big as the module, the module is maybe 3" wide and looks something like this,



p.s. I have no idea if those are the right part numbers for your car, that picture is just representive of what this sort of power module looks like more or less.

aah, another pic in place

 

Your title says hard to start hot, but your first post says it starts but runs rough. Which one is it?

My guess would be the crank sensor or power stage like others said. My 740 had hot start probs but the ignition would be dead. Power stage was dying.