Chevrolet Repair: High Idle & dies at take off !!!, air control valve, vacuum leak

Question
Howie,

I just purchased a 89 Chevy 3500 with a stock 454....It starts fine but idles real high at cold temp. it idles fine sometimes then idles high again after running a while. when it starts idleing high it floods out on take off. I pulled the air filter and the left side ( pass side ) injector is putting out a mist, were the right (driver side ) injects a full spray and makes a clicking sound...when I pull this injector plug it idles down.

What would be the best solution to solving this issue...this is a solid truck and just needs some attention to get back in prestine shape. would dealers still work on this year model truck?

Thanks in advance

Rusty Holliday

Answer
Hey Rusty,  Cool name.


  You need to concentrate on the idling system by understanding how the computer manages idle.  The ECM uses a servo motor that extends and retracts to manage a controlled vacuum leak.  This valve is called the Idle air control valve IAC.  The IAC could be sticking or not extending or retracting properly.  If there is a vacuum leak the IAC will fully extend and try to lower idle.  The computer receives an input from teh ignition module for RPM reference.  It has a target idle, lets say 900rpm and will retract or extend this valve to get to that goal.  If the engine has a vacuum leak the ECM will not calculate that air and be unable to manage idle.  Check for leaks around the thottle body.  The base plate gaskets get brittle and crack sucking them in.  Check the pcv system and check the brake booster line.  

Wayne