My truck has idled a little high ever since I have owned it. I dove into it a little today to attempt to figure out what was going on. It idles around 950-1000 RPM when cold or warmed up. I removed the hose that feeds the IAC and held my finger over the inlet. No vacuum and no change in the RPMs. I took the hoses from the throttle body intake and looked in there at the blades. They seemed to be closing completely and were very clean....too clean. I think the PO had used some carb cleaner or something on it. This can remove the coating and cause air to leak by.

The blades each have a 1/8" or so hole in them as air bleeds. I wiped the blades off with brake clean on a rag and put a small square piece of Gorilla tape over each one. I then started the truck. PERFECT, it idles at 750 rpm and now the IAC is pulling air and controlling the idle just like it is supposed to. The air bleed holes combined with the leaky blade seal was just providing too much air at idle.

I will find some small rubber plugs (GM had a recall that used them to plug air bleeds in blades back when they had the throttle body sticking issues) from one of my old tech buddies and fix it permanently. Alternately the throttle body could be taken off and the holes welded up from the back. May be other fixes but the fact is if your blades are leaky, this is a viable fix.

 

I had same problem on my '92, 300. Cleaned the blades with soapy water, and used HVAC tape. Worked like a charm.

 

I drilled my buddy's throttle body holes 1/32 larger than stock. his high idle is driving him nuts.

 

I have some of that tape, the aluminum with the paper backing. It is very tough and usually sticks very well. How long have you had it on there? I may just put some on there and call it good.

 

I've had it on for nearly 3 years. Still working good and around 4000+ miles later.

I figured the tape would do better and not want to become to brittle over the years.

 

Thanks for the tip guys. About a month ago I cleaned my throttle body with tb cleaner, 190k miles on truck. Had high idle so replaced vacuum lines, no change, saw your writeup, and used hvac tape worked like a champ, idle back to 650 in gear

 

Glad it helped you wag, that's why we post all this stuff.

If you find now that your throttle is a little sticky from closed, crack the idle screw in just a touch and it will fix that.