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?

[pm26]

Well, if your thermostat is stuck open, your coolant temperature will never reach the required temperature (the engine will run too cold) and the computer thinks the engine is not fully warmed up and therefore the idle is high. So I guess a thremostat stuck open could potentially cause high idle condition. Does your temperature gauge indicate lower than normal (ie. middle of the gauge) coolant temperature?

[sacnvr2l8]

Yes temp gauge sits just below 1/4 of the way warmed up and never over 1/4. I sprayed carb cleaner around TB with no change in idle. I guess I'll replace the thermostat and see what happens. Figured I'd have some other symptoms of a bad thermostat but i suppose if its stuck ope I wouldnt get over heating.

 

 

Well, if your thermostat is stuck open, your coolant temperature will never reach the required temperature (the engine will run too cold) and the computer thinks the engine is not fully warmed up and therefore the idle is high.  So I guess a thremostat stuck open could potentially cause high idle condition.  Does your temperature gauge indicate lower than normal (ie. middle of the gauge) coolant temperature?

 

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[pm26]

Sometimes you do not even need to replace the thermostat. What usually happens is, there could be a piece of dirt stuck between the thermostat housing the thermostat seat and prevents it from fully closing. Thermostats are spring loaded, therefore, something must usually be lodged there to keep the thermostat from closing. Anyway, replacing the thermostat and changing the coolant and flushing the cooling system is necessary in my opinion. If you have dirt floating in your coolant, the same thing can happen even when you rpelace the thermostat. so drain the old coolant and flush the system as well.

[sacnvr2l8]

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

 

Thanks

 

Sometimes you do not even need to replace the thermostat.  What usually happens is, there could be a piece of dirt stuck between the thermostat housing the thermostat seat and prevents it from fully closing.  Thermostats are spring loaded, therefore, something must usually be lodged there to keep the thermostat from closing.  Anyway, replacing the thermostat and changing the coolant and flushing the cooling system is necessary in my opinion.  If you have dirt floating in your coolant, the same thing can happen even when you rpelace the thermostat.  so drain the old coolant and flush the system as well.

 

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