I have a 2004 F150 Heritiage 4.2 V6. When it is cold the engine races up and down...slow then fast. When engine is hot it runs fine. This has really bugged me for some time...anyone out there has the answer?

 

is it throwing any codes... could try cleaning the MAF sensor... (i dont know where or if these have a idle air control valve if it does...could clean it)...

 

No codes at all...cleaned the MAF sensor...did not help at all...

 

Was wondering how much the RPM varies, thinking normal and the AC is cycling off and on. Something to think about.

 

x2..bill might have hit the nail on the head.... whats the fluation on the rpm... when its cold next time... shut the ac and heat off... if it dont do it... its just your ac compressor kicking on (also.. your ac compressor will cycle even on defrost)

 

Thanks for the reply...tried what you said... did not help...checked for vaccuum leaks...could not see or hear any...any more clues?

 

(Jim GO GATORS) I was wondering if you have fixed your idle problem yet. I have a 2001 with the same issue. Thank goodness we both live in a warmer climate state (Florida). It's driving me CRAZY also on those cold days of 50 or lower. Thanks, Alan

 

I still have the same problem...I did buy a new idle air control...did not solve the problem.I was told it might be the throttle sensor...I don't know what the rpm's are but mine will almost die seems like then speeds up fairly high...a lot more than the ac going on and off.But I did not have mine on any way.I will keep trying and if you find out anything please let me know.Thanks for the reply.

 

My idle goes from 750 to 1100 RPM's. Now, when it get alot colder (like above freezing) it does almost quit to 1500 RPM's. Crazy! No ones mensioned the TCS sensor to me. I'll let you know if or when I get it solved. Hopefully we won't have a lot of colder weather.

 

check for vacumme leaks.. start engine and spray it down with some carb cleaner... watch where you spray... if you spray something and it revs up... thats were its leaking