RPM goes down then up

J

Jefflovesarlene

Registered
Hope you guys can help me. I have a 98 Mark V111 with 125, 000 miles on it. About 2 to 3 times a week, I will get into the car and drive about 1/4 mile down the road, come to a stop or red light and the car's rpm will up a little then down and feels like it wants to cut off. I then put it in park and it goes away, then put it in drive and take off. Problem doesn't happen again until after it sits for a while then I start it up (ie go to work then on lunch break, start it up). Hope this makes since. Is it my transmission, tune up needed, etc. ? Ho:( pe it isn't gonna die on me.
 
Check engine light? With the A/C on?

Sounds to me like your IAC(Idle Air Control) valve is starting to take a dump. Its a cheap part and easy to change on your car, but I highly recommend have the car "scanned" for codes. Check your local AutoZone or find a mechanic that will do it for 20 bucks.

A good way to test if its the IAC valve is to use your foot on the gas to hold the idle where it should be, if you can do this, the majority of the time its the valve that has gotten stuck.
 
No engine light comes on while this is happening, no a/c is on either. When I give it gas, it does go away. I will check for this IAC. I really appreciate your help and hope to find the cure. I love my ride.
 
Sounds like the IAC valve bro :D SUPER easy to replace on the 97-98's! Get a TPS(Throttle Position Sensor) at the same time, with that mileage its good to change it. Make sure you disconnect the battery when you change the parts.
 
J said:
Sounds like the IAC valve bro :D SUPER easy to replace on the 97-98's! Get a TPS(Throttle Position Sensor) at the same time, with that mileage its good to change it. Make sure you disconnect the battery when you change the parts.
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Definitely IAC. The fact that it gets wacky at a certain cool engine temp means that it is getting stuck in a certain position (as dictated by the computer). Fortunately it is not acting up when it is warm, but you really should change it out, as it will only get worse.
 
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