Occasional High Idle

[southtj]

Awhile ago I made the mistake of getting the Firestone fuel system cleaner special.

Messed up my engine for a long time. Very high idle and bad fuel mileage. Finally after replacing the TPS and IAC all was well. That was a couple of years ago and now I've started having a slightly high idle problem but not the same as before.

It will idle fine at about 600 when parked or starting it up but when driving and then stopping at a light or stop sign it idles at about 1100. A very light tap of the gas pedal will bring it back down to 600 and all is fine until the next stop. Sometimes it's fine but more often than not recently it will idle high. Engine is the 4.0.

Any thoughts?

 

[JPNinPA]

Start with cleaning the TB and IAC. Check the connections to the IAC and TPS.

 

[Bounty__Hunter]

I would remove the throttle body and all the sensors, giving the throttle body a good bench cleaning. Could be the throttle plate sticks occasionally, could be a dirty plunger on the IAC.

Or upgrade to one of my 62mm throttle bodies ;-)

 

[69jeepcj]

I agree, clean it real good. sounds like throttle sticking a little. I have a carburator but mine has done that in the past.

 

[southtj]

I would remove the throttle body and all the sensors, giving the throttle body a good bench cleaning. Could be the throttle plate sticks occasionally, could be a dirty plunger on the IAC.

Or upgrade to one of my 62mm throttle bodies ;-)

Sounds like the plan for the weekend - cleaning the TB. I'd buy one Bounty if I wasn't going to sell it. I just want it to be running good for the test drives.

 

[Catoctin Jeep]

Bounty-Hunter are you pimpin your parts?????? :roll: Just messin with ya.
As far as the post goes you also may want to check the throttle cable. I agree that the IAC pintle maybe sticking.

 

[southtj]

I finally got it fixed last night after dealing with increasing problems since the weekend. Here is what i did to try to fix this slight high idle.

1. Took the throttle body off the engine, removed the IAC, the TPS and the vacuum thing I don't know what it does. I gave the TB a good cleaning with carb cleaner and a dab of oil near the spring where it was squeaking. Reassembled all and test drove it that Saturday afternoon. Ran fine, thought it was fixed. Didn't drive on Sunday. Monday it was worse than it originally was. Would idle at about 1000 or a little higher when coming to a stop and a gentle tap of the gas wouldn't stop it. I had to really stomp the accelerator to make it idle back down to normal. A few years ago when it did something similar I replaced both the IAC and TPS and problem was solved so I knew (hoped) that one of them was the problem again this time.

2. Ordered a new IAC online on Monday and it was there when I went home for lunch on Wed. Decided I had a few minutes so I threw it on and it was even worse. Started it up and it went up to 2000 rpms right away. I stabbed the throttle and now it was revving at 3000! Panic, shut down engine. Start it back up revs at about 2500 so I leave it and it slooooowwwwly goes down to about 800 on its own. Drive it back to work and it is constantly revving at 2000 at each stop. Stab of the gas and it sometimes drops.

3. Went to NAPA and picked up a TPS yesterday and installed when I got home. It is idling fine now but i've only driven it about 5 miles. Hopefully this fixes as I really don't want to spend too much on it before I sell it.

I just find it strange that doing those things not related to the TPS made it worse. Cleaning made it worse, new IAC made it worse. :???:

 

[JPNinPA]

Glad to hear you got it fixed. But, a proper cleaning shouldn't make it worse. Possibly dirt in the TPS or it was on it's way out.

I ran into an issue like this on the wife's car. Checking the air filter caused the TPS connection to come loose. It idled high until under 10 mpr. Took a bit to find the loose connection. Gave the TB and IAC a good cleaning as well.

 

[Bounty__Hunter]

Did you clean the carbon from the IAC housing? Did you clean the IAC plunger?

 

[southtj]

Did you clean the carbon from the IAC housing? Did you clean the IAC plunger?

I cleaned the TB and where the IAC mounts to the TB by spraying it real well with carb cleaner and scrubbing with a small soft brush. I did not clean the plunger on the IAC because I wasn't sure if I would mess it up or not.