91 2500 5.7L V-8 high idle

[sacnvr2l8]

I have a 91 2500 with 5.7 L V-8 it has high idle problems. I got lazy and took it in to firestone where they hooked up diagnostic to it. They said the thermostat wasnt working and that was causing the high idle. My problem is I have not other indication of the thermostat not working. no over heating heater works fine ect... could the thermostat be causing high idle? I was more inclined to think TB gasket IAC ect...Also they said water pump is leaking I found no leaks. Truck only gets driven about 1000 miles a year should i be concerned?

[GM-Tech]

I was more inclined to think TB gasket

 

You're probably right on with this. They suck a chunk of the gasket out and the extra air entering causes the idle to be high. This would be the first place I'd look.

[sacnvr2l8]

I looked at the gasket and doesnt look all that bad took some carb cleaner and sprayed around the TB gasket with no noticeable change in idle. Should I be thinking IAC Stuck?

 

Thanks

 

I was more inclined to think TB gasket

 

You're probably right on with this. They suck a chunk of the gasket out and the extra air entering causes the idle to be high. This would be the first place I'd look.

 

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[GM-Tech]

How did you look at the gasket? Did you take the throttle body off?

[sacnvr2l8]

I'm sure it seems kind of silly but no I just looked around the edges and the gasket looks intact. I replaced the thermostat and IAC and The idle is much better . It idles around where it should be the only issue now is the response from reving the engine back to idle seems a bit slow but i can live with that. Truck is getting old so may just get the throttle body rebuild kit for 40$ and do that but it is liveable for the moment

 

How did you look at the gasket?  Did you take the throttle body off?

 

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