SlackJaw

It idles fine at initial startup. But been having this annoying issue with the idle jumping up to 12-1300 rpm's after I drive and put the car back into park. If it sits for a few mins the idle goes back to normal (around 800rpms), but most of the time I'll shut it down at 1200 rpms.

The problems started after I cleaned the throttle body. I thought I had an issue with the IAC, so I replaced that, however the problem still remains. Should I have replaced the throttle body gasket when I removed and cleaned it? Not sure what would be causing this because it idled perfectly before I decided to clean the TB.

kissthis66

no need to replace the TB gasket unless its broken. I've yet to replace mine and i seem to be taking that thing off more than i do my hat lately lol.

to me it sounds as if possibly a throttle cable is not releasing or something. next time it does the high idle after a drive, pop the hood and see if the throttle is stuck open and is able to be pushed down/back to the idle positioning.

1990 XJ-Texas Edition

I'm having this exact same issue, and its been going on for a while now. I actually just got done deep cleaning the TB, including the IAC and the hole it goes in, and its worse now. Before, it would only jump to about the same as yours but now its staying at 2000-2100 rpms. When I started it, everything was better than before but not now. I haven't been able to test the voltage and everything that goes into that whole area because my multimeter is dead so its kinda just trial and error now.

1990 XJ-Texas Edition

Try fiddling with the arm on the TPS, tried it with move and if I fluttered it a bit the rpms would drop back to normal-ish levels. Maybe there's finally a cure for high-idle syndrome!

1990 XJ-Texas Edition

*tried it with mine*

JohnWongFat

I'm in the same boat, although I think my problem is vacuum related. However, I've troubleshot everything I can think of. Check to make sure the tube that's running from the throttle body to the map sensor is sealing. My grommet was leaking. If you spray it with throttle body cleaner, it would rev. Also, there is a throttle adjuster to the left of the throttle when looking at it. It's the smaller cable. Make sure the the throttle is closed, pressed the button, open the throttle to max, and press the button again. When you let it go, you may see a black piece of plastic move. I'm not sure if this will help, but mine was out of whack after cleaning it. I think affects your shift points somehow, but it can't hurt. I'll keep you posted if I figure mine out.

SlackJaw

i'm going to take a look this weekend at the cables and vacuum hoses around that area...kinda wish i didn't clean the darn thing...runs better dirty!!! lol

highmileage

I haven't cleaned my throttle body in a while, and I have had the same problem. It comes and goes, won't see or hear from it for weeks or months then BAM the high idle monster visits for a few days. IDK maybe its just age?

JohnWongFat

Gentlemen (don't worry, I use the term loosely),

Victory! I finally found the damn thing! Of course, like all my other problems, it seems to have lead to another problem. To start, I found that it was leaking from the intake manifold. I had tried spraying it (and every other thing I could think of) with throttle body cleaner to test for leaks, and someone suggested I use starter fluid instead. I did that and found the leak at the front of the manifold. The odd thing is that I got the opposite reaction I expected when I hit it with the starter fluid. When I sprayed it, the engine bogged down instead of revved up. I'm not really sure why. Regardless, after I found that, I quickly found that the bolt at the top of the exhaust manifold was extremely loose. I didn't even need a wrench to pull it out. So when it heated up, it would expand enough to leak.

Now on to my problem, I'm pretty sure that I'm missing a bolt on the underside of the exhaust manifold:

https://i.imgur.com/Y0tJi.jpg

There's a hole there that looks like it should have a bolt in it, but when I poke into it, it stops at the head. If there's supposed to be a bolt there, it's broken off in the head. Is it possible to use an extractor to get it out of there, or will I have to take it in to the shop?

kottobahn

If JohnWongFat hasn't gotten an answer yet, yes. There is definately a bolt supposed to be there. Probably snapped off on over tightening. If your lucky and, what I would try first is drilling a hole in the broken off bolt and using an easy out to unscrew the broken bolt. If that doesn't work then your going to need to drill out the bolt completely and helicoil it which may require you removing the header which is a phenomenal pain in the ****.

Has anyone difinitavely figured out a solution to the Renix engine and the high idle? I purchased my 89 XJ with 190k on it with a stock motor and it had the high idle. I have since: found and fixed an air leak, replaced the injectors with Neon injectors, put a pace setter header on it, replaced the IAC motor, adjusted the TPS, replaced the O2 sensor, replaced the EGR valve, put after market intake in it and tested the remaining sensors (CTS, TPS, MAT and MAP) and still cannot get the idle down below 1000 RPM's. .

After reading about the loose manifold with an air leak which has worked for other owners I have re-torqued the bolts on the manifold (three of the lower bolts needed tightening) and no good..

I can get the idle down if I disconnect the vaccum hose from the MAP sensor but I can't imagine that's working properly.

Anyone?