hot engine or cold or both,? and how high is high?
which engine.???? USA car, not the Export? 2.5 or 4.0L
why ignore that CEL lamp. the PCM is trying so hard to communicate
to you, so plug any scan tool on earth in that port, 16pin USA OBD2 port. (USA car?)
scan it , and get the codes. DTCs.
The car has MAP based system , called speed density.
all pro machinics knows that phrase.
the reason is Map BASED EFI , all race fast with air leaks.
what happens is the air leak is detected (the brain is clueless as to where) and the brain matches perfect fueling to said total air.
bam you are an expert. easy huh?
air leaks 101 (its is complex in diagnosis but IS simple physics.)
- why not state what too high is 801 rpm 1000, 2000 RPM.
- The plenum vacuum at near 20 inches.?
- All vacuum hoses leak free, or worse missing or fell off
- did you pinch all vacuum lines to find the leaker (rpm drops)
- is the throttle cable set tight? it must not ever be so.
- is the Throttle valve full of gunk blocking is close up.?
- the key to finding this is blocking all air paths 1 by 1.
- The engine coolant never reaches and holds 180F + temp.
- The fast idle input to the PCM is true.
- Some one hacked the throttle stop(factory set?)
- see magic below:
the IAC motor never fails but does love to stick
cleaned my 3 jeeps like a 100 times. in 500k miles total.
its just a simple stepper motor.
keep in mind fast idle speed is a feature of the ECU.
to prove i have leaks , on my 4.0L
i removed the IAS stepper, motor. and unscrewed (causing closed
then put it back with no connnector. and started the engine.
it hot idle screams YOU HAVE AIR LEAKS.
acid test, no engine can run with zero air supply, that is my magic.
controlling ALL that air. what ever that takes.
more data here.fsm words.
The PCM is also equipped with a memory program that records the number of steps the IAC stepper motor most recently advanced to during a certain set of parameters. For example: The PCM was attempting to maintain a 1000 rpm target during a cold start-up cycle. The last recorded number of steps for that may have been 125. That value would be recorded in the memory cell so that the next time the PCM recognizes the identical conditions; the PCM recalls that 125 steps were required to maintain the target. This program allows for greater customer satisfaction due to greater control of engine idle.
Another function of the memory program, which occurs when the power steering switch (if equipped), or the A/C request circuit, requires that the IAC stepper motor control engine rpm, is the recording of the last targeted steps into the memory cell. The PCM can anticipate A/C compressor loads. This is accomplished by delaying compressor operation for approximately 0.5 seconds until the PCM moves the IAC stepper motor to the recorded steps that were loaded into the memory cell. Using this program helps eliminate idle-quality changes as loads change. Finally, the PCM incorporates a No-Load engine speed limiter of approximately 1800 - 2000 rpm, when it recognizes that the TPS is indicating an idle signal and IAC motor cannot maintain engine idle. A (factory adjusted) set screw is used to mechanically limit the position of the throttle body throttle plate. The IAC motor through the PCM controls all idle speed functions.