High Idle in P & N When Warm

Post by **asg1986** » 01 Mar 2010, 02:04

Hey All,

Hoping to get some ideas here. I've been experiencing a high idle of around 1200-1300 RPM when the car is warm, but only in neutral and park (when the transmission is engaged the idle drops to 900 RPM). I've checked all the typical places where vacuum hoses would leak, and I replaced the IAC valve per my mechanics advice. Should I get a MAF from the Pick N' Pull and see what happens? Is there anything I can unplug to test the various suspects?

I don't have an CEL or any other lights on. Again, my mechanic thought it was the IAC valve, but I replaced that with a known working IAC valve.

Any and all ideas are appreciated!

Andy
1997 855 n/a

icelandic · Post by **icelandic** » 01 Mar 2010, 04:41

Park the car in a safe place and leave the engine running in P. Pop the hood open and remove the black cover over the throttle body. Take a gogod look at the entire assembly and without touching anything take a good look at the idle adjustment screw on the back side. See if it is touching its stop. If it is not, move the brown wheel where the accelerator cable is attached to and see if the adjustment screw goes to the correct rest position, and rpm drops to normal level.

If this happens, it means that something is preventing the throttle plate to return to its rest position.

Some possible causes:

1- Dirt in the TB- remove and clean
2- Lack of lubrication on the cable pulley or on the TB plate axis and spring: clean and lubrify
3- The connecting rod (the black one with two ball joints) may need to be adjusted. It has a nplastic nut in its center, and by untightening it you can adjust its lenght.

Post by **asg1986** » 02 Mar 2010, 14:11

I checked the throttle body, and it was in the correct position, and seemed to be moving fine... Any other ideas anyone?

icelandic · Post by **icelandic** » 02 Mar 2010, 14:36

If you are asolutery certain that the TB plate is reaching the fully closed position, my only two other ideas are a vacum leak or perhaps leaky fuel injector or injectors. Another possibility would bea faulty fuel pressure regulator, but if this is starting to fail, you would be having a slight difficulty in hot starts (having to crank twice- on the first crank it does not start)

VolvoTrooper · Post by **VolvoTrooper** » 03 Mar 2010, 10:54

Is your temperature gauge reading low? Replace your thermostat and coolant temperature sensor. The ECU may think that the engine is still cold and is providing a richer fuel mixture, hence the higher idle when warm.

Post by **polskamafia mjl** » 03 Mar 2010, 11:31

The temp gauge advice is good. This is a bit of a side note, but the throttle plate is never supposed to be fully closed; that would suffocate the engine.

icelandic · Post by **icelandic** » 03 Mar 2010, 12:09

I agrre on the temp sensor, but disagree on the TB plate. It can be on the fully closed position. The air for Idle is not regulated by the TB but by the idle controller that has a separate air feed, after the TB plate. If the TB is slightly open at idle, minimum RPMs will go above normal 830 rpm.

Post by **asg1986** » 07 Mar 2010, 17:06

Temperature gauge is reading right in the middle, and the car heats the cabin quickly. If my memory is right, the high idle began following the replacement of my rear oxygen sensor. At the time I thought something else must have been causing the high idle because the sensor was brand new. Could this be the culprit? The sensor was a bosch replacement recommended by AutoZone-- but it was generic in that wires needed to be cut for it to connect to my car... Maybe?

Thanks for all the feedback!

Post by **asg1986** » 08 Mar 2010, 17:45

It idles high all the time actually-- it is more apparent to me now. Might be the warmer weather...

Post by **asg1986** » 11 Mar 2010, 15:55

I couldn't figure it out so I took the car to my mechanic. It turns out the throttle plate did need to be adjusted. The metal is supposed to rest on the bolt, but then it is supposed to be tightened another 1/2 turn (or something like that). However, this still didn't fix the high idle. They unplugged the oxygen sensor that I replaced, and that had no affect. They also checked the AIC valve (which I replaced), and saw that it was still good. The didn't find any leaks either. He plug it into his scanner and found that it was idling high because of a lean fuel/air mix).

I just stopped by, and this is all the stuff they went through. I'm bringing it back tomorrow. He's an awesome mechanic (Ken at Volvotech in Lake Bluff, Il). He thinks its either the air mass meter or something else. Guess I'll find out tomorrow!