for high or surging idle - if the new IAC doesn't fix it, replace TPS.

 

What I am looking for is any kind of system check ect. The broke one I put in lets me drive the truck (hand set possition), but the PCM doesn’t seem to care that its not responding to its commands (I say this because I get no MIL). I do know the system test can catch the one faulty IAC so it knows the IAC is there. Maybe the PCM isn’t sending positioning data because some other sensor/reason. That’s why I’m looking for a test I can perform.

 

Its not that kind of idle problem. The IAC isn't moving and the new one comes at a full open pre-set possition. If I cover my hand over the air bypass port of the IAC, the engine idles fine. The darn thing will just not move!

 

Ok, here is an update. I changed the IAC again and still the same thing. It w/n move. I checked the wires to the PCM for opens and shorts and there were no problems. That leaves the PCM or the PCM isn't moving the IAC motor due to some other input.

If anyone knows of a test, that would be great. I used my OBD II scan tool and the map sensor looked good (read aprox baro with no engine running and a change after running that varied with the throttle). The TPS read 14.1 at idle and varied smoothly thru pedal depression. Still no engine light came on.

From what I found, the IAC moves with considerations from m a multitude of sensors to include:

the brake switch, speed sensors, engine temp, O2, TPS, coolant temp and may more.

I am leaning toward the PCM being bad but have never had to change one. Will I have to program the new one? If so how do I do it? I have heard of programmers that you can buy, that will download your current program, then up-load a new better fuel efficient program while saving you old one. Can I use one like this to save my current parameters and then transfer them to a new PCM or even make the new PCM better with the program offered by the programmer company?

Please any advice or past experience with programmers, PCM’s, or any problem like mine would be appreciated!!!!

Thanks,
Kurt

 

its hard to say what's wrong, but you are correct about the multiple interactions.

if the TPS is telling the PCM that your foot is in the gas, then it doesn't operate the IAC.

don't assume its the pcm until you test everything with a scanner, and verify that all sensors are reporting correctly to the pcm.

if you do get a pcm from the junkyard or refurbisher, you need to match the year, engine, equipment, etc. if you live in a place with emissions testing, the proper VIN number and mileage needs to be flashed in. refurbishers do this. dealer will do this but only on a NEW pcm and they charge a fortune.

tuners only replace a few parameters in the pcm, such as fuel and timing tables. it won't fix a flash from improper year or transmission or engine.

 

Grab a friend. Park said friend in drivers seat. Disconnect battery, turn on headlights, turn off headlights, reconnect battery. Turn ignition to run, while you are staring down at the pintle of the IAC motor, it should close all the way, and then back off a bit. (this is how the PCM relearns IAC position.) If it doesn't do that, repeat the test, but, have a meter on one of the power wires, and see if you get anything.

 

Interesting about the TPS... Do you know what the correct parameter value is? My scanner gave a value of 14.1 with my foot off the pedal.

I am looking at upgrading my scan tool for either an Autotap or a Palmer ScanX Professional. Do you (or anyone else) know anything about these tools? Do they test systems like the DRB tool where you can simulate inputs etc?

Thanks for everyones help

Kurt

 

It that 14.1 % ?

 

I wish I knew! POS scanner d/n tell me anything about what I am looking at, what range is acceptable etc. I was hoping you might recognize the value.

 

Do you have a Haynes manual? You are much better off testing the TPS with a multimeter. The procedure is in it.