markdarbypearson
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I have the hunting idle problem. Happens intermittently hot or cold. Throttle body has been off and iac valve taken out and whole lot cleaned. Next move??
General Hunting idle
- Thread starter markdarbypearson
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Currently reading:
General Hunting idle
Mike1alike
Established member
Mike1alike
Established member
And related to hunting idle, I've recently discovered the following:
If on idle the engine speed drops down to about 500 RPM that is caused by the cooling system. It's either air in the system either broken excess pressure relief valve so to much pressure. In this second case, the radiator hose is quite stiff. The valve is located in the radiator cap (or expansion vessel cap) and the fix is replacing it with a new one.
This is how it looks like:
https://ibb.co/cgmMxMy
And another scenario related to hunting idle is the opposite situation, when the engine revs up by itself above 2000 RPM and to even 5000 RPM. There is usually a crack in the air intake system and it can be from the air filter, the hose (if have any) or conduct, the intake manifold and all of it's gaskets, there are several and I've mentioned this fix in the above link's post.
Another causes for high rev can be: using the AC on cold season (rev goes up to 2000 RPM), dirty throttle flaps, broken sensor - one of the throttle position sensor or MAP sensor or broken Idle air control valve .
If on idle the engine speed drops down to about 500 RPM that is caused by the cooling system. It's either air in the system either broken excess pressure relief valve so to much pressure. In this second case, the radiator hose is quite stiff. The valve is located in the radiator cap (or expansion vessel cap) and the fix is replacing it with a new one.
This is how it looks like:
And another scenario related to hunting idle is the opposite situation, when the engine revs up by itself above 2000 RPM and to even 5000 RPM. There is usually a crack in the air intake system and it can be from the air filter, the hose (if have any) or conduct, the intake manifold and all of it's gaskets, there are several and I've mentioned this fix in the above link's post.
Another causes for high rev can be: using the AC on cold season (rev goes up to 2000 RPM), dirty throttle flaps, broken sensor - one of the throttle position sensor or MAP sensor or broken Idle air control valve .
Last edited:
The cooling system pressure relief being stuck cannot cause excessive pressure unless there is another cooling system fault. The valve in the cap does not open during normal operation. If it did you would quickly loose all your coolant.
Mike1alike
Established member
If you put cooling liquid above the max line, it can cause excessive pressure. I did that and that is exactly what I got: excessive pressure that did not got out of the system through the valve, the valve being stuck.
