99 xlt idle problem. please help.....

[elf4u]

hello..

i went to the ford dealer to get my idle problem fix...
but it still the same...

when i drive around and stop at a light. the rpm goes to 1500 then doesn't come down..

i went to the dealer and the replace the IAC. but the problem is still there....

any idea??? the dealer told me that they have to upgrade the pcm.. (more money)

please help....

 

[pmcmaster]

Sounds like the IAC but the Crankshaft position sensor (CKP) also plays a part in engine speed control. Is the engine management light on (MIL)? if so you need to get any error codes checked.

 

[elf4u]

no the engine management light is not on....

i tried cleaning the throttle body... (it was really dirty) i took it for a test drive today.
and it seems okay.. but i have to see.....
but now my idle is at 500 then 600, then back and forth.....
any suggestion?

 

[Ken99EB]

Watch your temp. gauge when the idle increases. I bet its your thermostat.

 

[TPLYNCH]

Even if your temp guage doesn't appear to be overheating, he Temp Sensor may be faulty, causing the PCM to think the engine is overheating.

 

[elf4u]

i changed the thermostat and the temp sending sensor...

at what does the rpm have to be??? 750?????

 

[TPLYNCH]

That's about right. Idle speed will depend on whether you are in Park/Neutral or Drive/Reverse. Idle will be a little higher in the former and lower in the latter.