Didnt find a vaccum leak but did see moisture between the brake booster and master cylinder.

 

How did you check for vaccum leaks?

 

I sprayed starter fluid around intake and tb and all vaccume lines involved with them. Pulled vaccume hose off brake booster check valve and plugged it. I blew thru the check valve would only let air pass 1 way so i assumed it was good but we all know what assuming will do for us. If there is something i missed would love to know its bout to drive me crazy. Its a project truck that i drive daily.

 

I still say its a vac leak. does it have a plastic intake?....seems to me I remember working on a 91 1 ton that had a fuel handling switch that did the same thing. what about bumping the idle up a little bit? is it set right? is the ICM (Idle Control Motor)set right? with no codes you are looking at a mechanical problem not electrical (transmission, valve timing ect) but I say its vac leak.....how much blowby does it have?

 

I remember having a simlar problem with an early 90's Suburban which is the same set up. For some reason I think it had to do with the vacuum line going from the throttle body to the vacuum canister. I am going back a few years so sorry if I am remembering wrong, but try this. Get a vacuum cap and just cap that line at the throttle body and see if that helps.

 

Intake not plastic, book said idle is factory set and caint be adjusted. When i changed the iac it idled a little high and ran fine, but at 40mph it resets it and went back to same prob. If i could idle it up a bump that would take care of it. I will try the cap. Thanks for your time its greatly apppreciated.

 

yeah it is supposedly set at the factory but I seem to remember an adjustment screw for idle right there where the throttle cable hooksup

 

Yeah but they put a stupid cap over it that is a pain in the *** to get out. You can drill it but you have to be quick with the drill once it breaks through or you will mess up the head of the adjustment screw. You shouldn't have to mess with that though.

 

true you shouldnt have to because you are just hiding the real problem. If its not a vac leak then I would venture to say it is a possible valve train or ignition issue