Gimmy

Okay so I ran through the forum searching for answers. Even took the time to clean up and replace grounds. Eliminated the c101 junction.

This is an 87 renix XJ 5spd.

Problem: starts and idles fine. But over the course of 15 minutes (warming up) the idle will slowing start to increase. Sometimes up to 3k. Normally around 2k.

My thought is obviously something is getting warm and allowing the idle to jump up.

But. If I shut it off and start it again it will idle fine. But then jump up within minutes.

Any info on this at all? I'm stumped

DFlintstone

You probably should start by cleaning your IAC. (Cruisers #11) When that didn't work as my 90 was acting exactly like yours, I figured out it was just the plug to the IAT was not always making a good connection.

Cruisers tips are right on top in my link below.

Gimmy

I replaced the iac. Had it on warranty. Not to say it's not a bad factory part

Gimmy

Where is the iat?

EZEARL

https://www.cherokeeforum.com/f2/87-...sensor-194439/

DFlintstone

It's rear of the TB, sticking up out if the intake manifold with two wires. It's a pretty minor player, I think.

In your shoes I suppose I'd make sure the TPS is adjusted. (Cruisers #11 I think). Something you want right anyway. Btw, I would make sure it's not that IAC plug. The way it faces up moisture can "do things" in there.

Air getting in, (one way or another), is why the high idle I think. It could be the intake manifold when it warms up. I have this "canned" >>

Vacuum leaks suck. I go around with short little shots of starting fluid, if you hit one the sound of the engine will change. Small little shots! You don't want that stuff to accumulate. It's a fire hazard, but It evaporates right away. Also with a tube, or a section of hose you can listen for it. Don't forget the lower O rings on the injectors need to seal as well. (uppers would leak fuel).
The manifold bolts have a habit of loosening, especially that rear one. On anything like that you never want to tighten only one. It can warp/bend, even crack things. If I found that any that where easy to reach where loose, I'd pull the air cleaner and tighten them all, starting in the middle and working out towards the ends. I go over about three times. It's a bear of a spot to get a torque wrench on them all. Just don't ape on it. If its firm and not turning, no point in going on to break it, a REAL *****. The rearmost bolt underneath takes a little doing, but it can be done with the right extension. For that very back one by the firewall I use way long extensions (18"), with a swivel at the socket. Anyway, that's a good thing to check on any old Jeep. ALSO, there is a large line coming off the intake, rear of the TB that goes back to the firewall, across, then forward down to the vacuum ball behind your right front bumper. You can pinch that off or unplug it and cap the nipple to test if you have a leak there.

Gimmy

Awesome info. I will have to tinker around with it more once home. The manifold is something I never thought of. Getting hot and expanding to allow air in. Thanks for the info

briankk

. ALSO, there is a large line coming off the intake, rear of the TB that goes back to the firewall, across, then forward down to the vacuum ball behind your right front bumper. You can pinch that off or unplug it and cap the nipple to test if you have a leak there. [/QUOTE]

Oh, excellent! I have the other fast idle thread going. Per your suggestion, got my needle nose vice grips and started pinching hose. 1st one was the line to the brake booster, pinched it off and idle dropped to 1000 rpm, or a tach needles width less. Capped the tube and the engine idles just below 1000, and "hunts" there, just enough so you can hear it. Guess I need a new brake vacuum valve, and to keep looking for a smaller leak. That tip saved me an afternoon of squirting and cussing, thanks a bunch!

Gimmy

Hey I really don't need to know what you do in your free time...

cruiser54

Make sure your intake manifold bolts haven't loosened up. Of my Tips, which ones have you completed?

Gimmy

I did the grounds by the dip stick. The c101 replacement. Cleaned out all connections I saw including the ten pin on the driver side. Cleaned and tightened the prongs under the coil.

NOTE: I replaced the iac and Tps because they were under warrenty. So far no money has gone into this problem

cruiser54

Good.

Has it always done this? Did you adjust the TPS on the "engine" side?

Gimmy

It has always done this. I picked it up a week ago. I did not adjust the Tps the right way (multimeter) I need to do that. But the symptoms didn't change when I changed the two sensors

cruiser54

Click on my Tips link and go to Post 14. Maybe somebody screwed with the adjustment of the butterfly.

DFlintstone

Well, you're welcome! Glad to help. I'm not familiar with failed diaphragms in brake boosters. (not thinking it's a check valve, Idk) Hopefully the isue will be resolved in your thread.