i just replaced the GEM module or ESOF module yesterday to try and fix my 4x4 problem and now i have another problem. it was a used module from a junkyard by the way. after i replaced it the truck started to idle up and down all by itself at random. it will idle down to about 500 then up to 1000 and then below 500. then it might come out of it for a minute then it will just stall. as long as i hold some pressure on the gas pedal and keep the idle up it won't do it. it has even stalled when i'm driving on the highway when i let off the gas. it totally does this at random but fairly conscicently. it will always start right back up real easy but it just stalls again eventually. i put he old module back in hoping that would fix it but it didn't. now i have 2 problems instead of just one. just wondering if there is some programming that needs to be done for the different moule

 

The GEM has little to nothing to do with the engine idle under normal 2w or 4H conditions..
The IAC controls the idle from the PCM not the GEM.
If you can't see a problem with the IAC, you can always change the Gem back to the original one to see if there is a connection for some other reason.
The only connection the GEM has with the PCM is in 4L where it signals the PCM to change the program shift points due to the low gearing involved.
Good luck.

 

i allready switched back to my old GEM module and still does the same thing. i don't understand why the old gem would have to be reprogrammed if tit was allready set for my truck

 

The original still has the 'as built' program.
It does not change just because it was removed.
The 'firmware' is semi permant unless a forced change is made with a programmer from outside.
You have some other obscure issue you have to find.
Do this; start the motor and raise the idle by throttle. If the motor runs at high idle without any issue, the IAC is not being controlled by the PCM to hunt for the correct idle.
Remove IAC and spray clean the inside making sure the pintel can move freely and return under it's spring pressure.
Spray clean the throttle body and plate until it runs out clean.
After reassemble, power down the PCM for a few minutes, then start the motor under some loads with the heater fan on high, headlights on etc to offer the motor the type of worst case loads it would see under cold starts.
The crank sensor feeds back the RPM data to the PCM so it can rebuild the cold start tables vs temperatures.
This also goes on for hot starts vs temp.

Good luck.

 

what do you mean by power down the pcm and where would the pcm be located

 

Either pull the PCM fuse and test for being blown or remove the battery cable for a couple minutes, then reconnect.
This clears all the extra data out and leaves the base program tables to re-learn cold start all over again.
Good luck.