I have a 1992 240 with about 130K for mileage. I have owned the car since it was new and have done the majority of the work on the car. Anything I can do without a lift, I try to do myself.

The car has been running rough when first started. Once it gets up to temp it is running like clockwork. But the 10 minutes while it warms up it runs rough and hesitate when I step on the gas.

Replaced all ignition wiring, distributer and cap when is first started.

No check engine light.

I got code 2-3-2, "Fuel system compensating for rich or lean mixture at idle". I am trying to rule out the possibilities. I believe it is the coolant temp sensor. Hoping it is not the Idle Air Control Valve.

Any thoughts or experience would be appreciated. I can do any testing I need before buying parts, as these are all expense parts that seem to be in play for this problem.

 

Did it run poorly when first started during the summer? How about warm/hot restarts, such as when running errands? Just the first start of the day? It isn't the IAC; that really just affects the idle rpm, not the quality. I believe by 92 they had done away with the cold start injector...I know 93's did not have them. W/o a cold start 5th injector, engine coolant sensors play an even bigger part in cold starts. A lot depends on what maintenance has been done recently. Quite honestly, often a number of items can be operating at low normal and the combined result is poor performance. For instance, worn/fouled plugs don't fire well when cold. A leak in the exhaust will make a functioning O2 sensor think the mixture is lean and tell the ecu to richen the mixture which fouls the plugs. Bad plug wires, worn rotor and cap...all will tell their tale as the weather cools off.
So, my question is: Where are you with service on the car? That dictates a lot as to where to go from here.

 

I have done most of the maintenance on the car. So I know what has been done.

The problem is fairly recent, so this summer all seemsed well. The problem is only an issue when the car is cold, or has cooled down. If the car is warm and I runa quick errend the car is fine on start up. Once it reached temp all is well.

I have just replaced the rotor, distributer cap and all ignition wiring in the last month. The exhaust had a leak in the manifold, but I took it to a shop to get repaired 3 weeks ago. So the exhuast is tight now. Plugs have not been done in about 3 years.

 

Well, then, sounds like it may indeed be the ecs. Here's a decent diagnostic write up...
http://www.swedishbricks.net/700900F...e Sensors, Etc

 

I have some new codes that have registered on the car. The check engine light came on, and I now have 3 codes.

2-3-2 Fuel system compensating for rich or lean mixture at idle
2-3-1 Fuel system compensating for rich or lean mixture at cruise
2-2-1 Fuel system compensating for extreme rich or lean mixture at cruise

I have not changed out the coolant temp sensor yet. Do you think these same codes are evidence of a single problem with the ECS?

 

Well, before you replace, diagnose...this article concerns the 7 series, but the motor is the same as yours...
http://www.swedishbricks.net/700900F...e Sensors, Etc