1991 Ford Explorer
Starts and runs fine in cold weather (if truck engine is cold or warm).
Starts and runs fine in warm weather (if truck engine is warm).
Problem is ...

In warm weather (say 60 degs F. or higher) when the engine is cold,
when I initially start the engine it runs rough for few seconds and
then will either stall or begin to run fine. IF engine stalls I am
able to start the engine and it will run fine.

Any ideas on what to troubleshoot, test, etc. would be appreciated!

 

id run a fuel pressure gauge at a time its most likely to act up. that way you can hook up your fuel preessure gauge have an assistant start it while you watch the gauge see what is happing at the moment it stalls. Note rather the pressure is within range while its running and confirm that the pressure doesnt come down for at least 5 to 15 minutes after you haved turned the car off and have the key in the off position. if it stalls while your testing try to notice rather the pressure drops before stalling or if it stays the same and it just dies. To be honest it could be as simple as a fuel filter but without testing I couldnt say for sure. If the car is older and the filter hasnt been changed in a recently it certainly wouldnt hurt to replace it and hope for the best so you dont have to play hell trying to trouble shoot it. filter could clog up temperarily and cause the problem, fuel pump could not be pumping high enough pressure temperarily, could be the fuel pressure regulator is releaseing pressure and without the required pressure it would cause the engine to run rough or stall. It could even be as little as bad plugs. If it where me Id change fuel filter and spark plugs justbecause itsgeneral maintenance anyhow and maybe the problem will be corrected if not do fuel pressure test and let me know what you come up with. Oh and to help me rule out other options here when you go to start your car dont hit the brakes as your starting it up. if you hit the brakes while cranking the engine and there is a vaccum leak,, especially in or around the power brake booster or hose it could cause the stalling and rough running condition.