A minor but persistent (year-long) rough idle on my 1991 240 has quickly turned into a Cold Start Nightmare over the past month:
SITTING HOURS OVERNIGHT (50 to 60-degree temp. overnight) - When I attempt to start in the morning, the engine idles high for 3-5 seconds and then immediately dies. To successfully start, I must keep pressing the accelerator pedal at least half-way down for 2-3 minutes. The engine sputters, almost backfires, shakes, lopes, almost dies, etc. After 2-3 minutes, everything runs just fine.
WARM ENGINE SITTING - Once the engine is warmed up, it will consistently start withouth problems. Still a slightly rough idle, but OK. The car does not die.
I have changed the battery, coolant temp. sensor, and spark plug wires. Any suggestions would be greatly appreciated.
Sorry if this is insulting, but I don’t know your level of expertise. The coolant temperature sensor you replaced - was it the single-wire sensor toward the front of the engine, or the the two wire sensor toward the rear that you can barely see or touch without removing the intake manifold?
The tough-to-reach two-wire sensor is the suspect with these symptoms.
My knowledge is amateur at best, so no offense taken. I replaced the coolant temp. sensor that goes near the manifold. Initially, I still experienced the same symptoms, but lately they have stopped. Would you suggest that I replace the the single wire sensor called the Temperature switch?