My idle seems a little low and was wondering if anyone knew what the proper idle should be on my 99 4.6 auto? Mine is 6-700 RPM's (warm) in gear at a stop and, an even 1000 RPM's on freezing cold mornings in Park. My buddy has a 03 5.4 FX4 and idles about 12-1300 cold? We checked today leaving work. The problem is when I start it on "cool" mornings it starts then idles way down for a split second then revs up to hi idle all with in seconds. Now, it's like 0 degrees outside (burrr) or in the single digits here in Iowa and when I start it, it starts then instead of idling down for a split second it dies. Acts as if the idle is too low because if I start it just touching the gas it revs up on hi idle and is fine?? Also, when it is completely warmed up and I have like the heater on I hear it slow down when I stop at a red light and the steering is a little stiff as if the RPM's are too low?? If the RPM's seem low, how do I go about raising the idle, is there a idle adjustment on it or is it controlled by the computer?? Tune up maybe?? I also wondered if the idle and hi idle is adjustable seperatly allowing me to possibly raise the hi idle and leave the warm idle alone? Any help or ideas would be great?

 

Sounds like a dirty IAC valve. Pull it off and clean it with some throttle body cleaner. As it has a gasket and you might tear it when removing the valve I would pick up a spare at the dealer before removing.

JMC

 

idle should be the same in park and in drive. mines about 800rpm. yours is probably in need of a good cleaning.mine had the same symptoms,gave it a good cleaning, she idles great now

 

To finish off the question of what is the proper idle.
It is set in PCM program as about 650 +/- a small amount.
The actual idle is determined by inputs from the ECT, the IAT and load sensing inputs the PCM has from lighting loads, A/C loads and transmission loadings.
This results in pulsing the IAC to maintain the right amount of by-pas air around the throttle plate to get the engine to match program value.
Plus there is a timer in the software that will keep the idle higher in very cold temps then slowly come down to the normal range.
Any faults in the major control such as the IAC will result in all kinds of action.
You should see very close to 650 at full hot run conditions.
The PCM 650 value is constantly trying to be achives by trying to control the engine hardware to match the software value by sampleing the crank and cam position sensor outputs.
If there is a miss match then the results can be any type of reaction from to hi idle, to irregular idle, hunting, to stalling because the full control functions are not working correctly as a loop action.

 

Thanks, I give it a cleaning when it warms up a bit.

 

Uhh, could someone show me in a diagram or pic where the IAC is exactly on a 99' 4.6? Thanks.

 

Here is a Diagram:




JMC