Car reves up and down at idle

[Rich00033]

Any body know what would make my 94 mark 8 rev up and down at idle it only does it when its warmed up???

 

[mag]

Possible ICV http://www.partsgeek.com/catalog/1994/lincoln/mark_viii/fuel_injection/idle_control_valve.html

 

[Rich00033]

Thats what I was thinking to could the egr cause something like that to

 

[Rich00033]

Do you know of the iac being bad would cause a loss of power when the motor is warmed up and would I make it die at red lights with the a/c running??

 

[mag]

Pull codes before changing parts [ It's called a Idle Air Control Valve think about it) It allows the ECU to maintain minimum RPM irrespective in engine load it is sometimes called a anti stall feature

 

[chris2523]

vacuum leak

 

[billcu]

My 98 does this, but only once, as it is warming up. I only notice it at a stop. If the car doesn't stop during warm up, nothing happens.

It's like someone is revving the engine a little. I put it in neutral, rev it up a little myself, and it's fine again.

I replaced the IAC but it still happens. I was thinking my problem might be the throttle position sensor, but the vacuum sounds like an easy place to start.

 

[Rich00033]

That is exactly what mine is doing to if you don't cut if off after it warms up it don't do that crap but if it's warmed up and you start it up it starts acting up I just put a new iac valve on mine and it still does it but it did get better and I'm about to do the tps and see if that helps

 

[Rich00033]

And keep in mind I am not throwing any codes at all when this happens so I can't pull codes that ain't there

 

[Rich00033]

And if it was a vacuum leak it would do it all the time I would think not only when it warms up and you cut the car off and start it back up then it starts leaking vacuum that makes zero since

 

[chris2523]

And if it was a vacuum leak it would do it all the time I would think not only when it warms up and you cut the car off and start it back up then it starts leaking vacuum that makes zero since

nah. cold start up maps are rich.
lean it out when it warms up and the problem appears.
btdt.