I have a perplexing problem. My explorer has the SOHC V-6 and will rough idle for a few seconds on semi-cold startup. Semi-cold means just a few hours of sitting. On a dead cold start after all night at 5 F, it will start up ok.
The engine will rough idle and smoke then something will click electronically and it will go right into normal startup mode and run smooth. It is as if the starting sequence is delayed. After that, it will run fine until the next semi-cold start.
My mechanic said no codes were in the computer. No check engine light. We replaced the idle-air valve but that did not work.
Smoke? Where does the smoke come from?
I’d check the coolant temperature sensor, but I’m more concerned about the smoke.
The smoke comes out the exhuast pipe. It smells of unburnt fuel like the mixture is too rich. Any ideas about the cause of the rough idle.
I think the three most likely culpripts would be: leaking fuel pressure regulator (fuel leaks past to the intake manifold); leaking fuel injectors (leak down into cylinders); failing coolant temp sensor (tells the computer the engine is colder than it really is).
For whom it may concern, it appears the problem was a leaking intake manifold gasket. Top gasket as I understand. Ford dealer finally found it.
Many thanks for the follow-up - glad you got it sorted out.