MyNameIsNick

Been trying to track this problem for a bit now. Basically it started intermittently. When I first bought it, it would idle normal around 900rpm or so. Occasionally when I would start it the idle would be at 1500rpm. Didn't think much of it at first. It got more frequent to the point now it only idles at 1500rpm. But what has me more concerned is that when cruising on the highway, the rpm's are higher than they should be. Normal at 65mph is around 2000-2100rpm. Mine cruises around 2400-2500rpm. Again though, when the problem was intermittent and it was idling fine, it would cruise at normal rpm's.

Today I replaced the TPS hoping that was the problem, nope. Tried the old plug the brake booster line and that didn't have any effect positive or negative. Thoroughly cleaned the TB a few weeks back hoping that was the issue. Have cleaned all terminals and connections. Tonight tried some tb/carb cleaner in the idle air control thing, did nothing but make it stall and the CEL popped on. Started back up just fine and doesn't run any worse or any less. Unplugged the battery to reset the ECU figuring the CEL was caused when it stalled while cleaning it. I found this vacuum diagram (http://www.jeepz.com/forum/attachmen...icture-071.jpg) to try and track down a vacuum leak (I think I can hear a slight one) but being that the problem was intermittent at first it makes me think it's more a sensor than a vac leak. Any help is appreciated as this is starting to irritate me.

1988cherokee

since you said you cleaned the TB I suggest taking a look at the throttle blade location to see if its open to far. I cleaned mine and had a problem like yours and it seemed that the previous owner adjusted it open for some reason and when i cleaned the junk off of it now the blade was open too far

MyNameIsNick

Thanks for the tip man but I had already checked that when I cleaned it being that was my first thought.

1988BlueBullet

When you changed the TPS, did you adjust it properly? Try adjusting so the voltage setting at closed is a little lower than spec.I think spec is 4.2 v, so try 3.9 v

notop46

Could be the Idle Air Control valve. It is a stepper motor in the throttle body that opens when the engine is cold to let more air in to idle higher. When mine went out the idle jumped to 2200 RPM. I could shift thgrough the gears without touching the gas.

If you pul the rubber elbow above the throttle body off, there will be a 1/2" port of to the side of the throttle butterfly. If you put your finger over that port and the idle goes to a normal speed, then this is the culprit. If not, keep looking.

Good luck.

MyNameIsNick

How would I do that? I put it on exactly as it came off.

Thanks for the tip, I've give that a try.

Diesel

His is a 96, you cant on his.

Replace the IAC, Check the Map sensor and check every vac line and fitting.

MyNameIsNick

Ahh gotcha. Well since the TPS didn't fix anything I'm going to return it and pick up a new IAC (what do these cost if anyone knows off hand?). Although yesterday while driving to work, was sitting at a light and looked down and my idle was at 900rpm. Next light it was back up to 1500.

Diesel

About the same price as a TPS. It definitely sounds like the IAC.

The TPS would not cause high idle.

1988BlueBullet

If it's not adjusted properly the TPS will definitely cause a high idle. If you don't know how to do it take it into a shop and have them use a scan tool to do it.
I use a multimeter and bend a couple of wires inserted into the connector. Loosen the attachment screws and turn it one way or the other. Connect the negative lead to the connector D terminal (black wire - sensor harness brown with orange stripe) and the positive lead to terminal B (blue wire sensor harness white with black stripe). Output voltage with the throttle closed should be 4.2 volts.

Whoops, missed that his is a non adjustable 96...

Diesel

Only renix can be, glad you caught yourself lol.

MyNameIsNick

Good deal. Well the reason I was think TPS was because when it went out in my Focus, it caused it to rev to redline if the clutch was not in. Had to drive with the cruise on or on the brakes or it would have just kept accelerating to redline.