Chevy & GMC Vans

email Skippy, I remember he or his bro inlaw having a crazy problem like this.......

You've ruled out so many items, whatever is left has to be small and identifiable. I can't offer what that is, but keep asking around, it can't be anything not worth repairing as the truck runs well overall. I t does sound like some sort of sensor that "clicks" once warm, thus telling the computer to react with different metering.

Do you have access to a scan tool? Sounds like you will need to watch the scan data to see what sensor is going out of range. You could also try unplugging a sensor and see if it improves. The PCM will use default values then. I'd try that with the MAF sensor, IAT sensor, and oxygen sensors.

A plugged cat might cause that too.

Scott

Have you sent a PM to Skip yet!

dunedog is right , we chased the same thing down for over a month on a 92 that kept throwing a code 42 whick is a ESC electronic spark control . we spent over a month & 400 $ changeing parts & trying things , including a timing chain & gears . we finally just for shits & giggles changed out a coolant temp sensor i had lying on my desk .............& wouldn't you know , all the problems went away !!! we were friggin pissed .

good luck man !!!!!!

i'm leaning towards the same thing with yours , the motor runs fine when cold but acts up when warm . if the coolant sensor is telling the computer its still cold when its not, its going to run rich as hell till the computer knows the motor is warmed up .

does it smell like its running rich ? or smell like extra gas after it warms up a bit ?

A scan tool or a code reader will give you an idea where to start & whats going on . i just picked up a code reader on line for 32.00 $ & $8.00 shipping . it will help you figure a few things out rather than guessing .

I'm usually off the mark on quirky problems like this for the newer year models, but you might look into the pulsator. My '89 doesn't have one, but as I understand it, it resides between the fuel pump and the fuel supply line. I've read very long threads about these causing problems that are difficult to find and resolve.

Does your have the stove pipe?
Maybe the stove pipe valve is directing heated air from the manifold into the intake system.
And with the doghouse on, the heat is worse.
Just another thought........

You may want to pull the distributor. I have heard of a few cases of the gear stripping out in them and it runs bad or not at all. It's a long shot but a possibility especially with the mileage. How are the plugs and wires?

I had a hesitation in my 92 for the longest time. It turned out to be the EGR. Apparently it would stay open just a teensy, weensy bit. Just enough to cause problems