89 blazer idles rough and stalls when in gear
 

Please help, any advice greatly appreciated

i have a newly acquired 1989 chevy blazer. 350 tbi. no engine mods that i have found. it has a new dual exhaust with mufflers but no cats and headers. the egr system has been "deleted" somehow. there is no vacuum going to the egr valve. engine runs fine. 160-165 degree water temp. oil pressure 55 psi at start up and around 45 psi once warm. starts up fine and drives good. the only problem i have is once the engine is warm, if i pull up to a stoplight or stop sign, it will want to start loping/idling rough and stall out. if i put it in park rpms go up as normal and it is fine. if in park it will sit and idle perfectly all day. but as soon as i put it in drive it wants to lope and stall.

i have tried the following remedies to fix the problem. new air filter and new air canister and gasket, new spark plugs, new spark plug wires, new idle air control valve, and new idle air control valve wiring harness. Timing is good, no obvious vacuum leaks, throttle response is good, and good fuel efficiency.

I am going to try and rebuild the throttle body tomorrow. no reason to suspect it but that is the only thing i haven't tried.

any suggestions?

Just drawing on experience with other cars: Sounded like a vacuum leak to me. What vacuum does it draw while at idle? Idle speeds are often designated for when the engine is warmed up and in Drive. If it cannot maintain the proper idle speed under those conditions, there is a problem. But you already knew that.

I rebuilt the throttle body and no luck, same issues. I tested every vac line I could find and also no luck. Everything holds pressure and looks fine. I then unplugged the iac valve and it went to running fine. No stalling. I suspect that maybe it is not working correctly because of the egr delete stuff but that's just a guess. Does anyone have any thoughts on why the ecm isn't controlling the iac properly? And are there any cons to running engine without iac?

1989 s10 blazer 4.3
 

Any luck