My XJ has started acting strange and I'm not sure why. It only started really getting noticeable when the weather got colder.
It cranks up and runs normally but, after about 5 to 8 minutes of driving it tries to idle REALLY high. At a stop light and in gear, it will idle between 1000 and 1100 rpms, and seems to run kind of rough. If I shift into Neutral or Park, it jumps up to 1500 to 1700. After about 15 to 20 minutes however, the idle speed will drop back down to normal and it runs smoothly again.

It's been too cold for me to pull the IAC to check it. I'm wondering if that may be an issue. I did unplug it while the engine was running and there was no change at all so, it may be done for.

 

Mine was doing that also. I did a full tune up and a new o2 at the down pipe and she's fine. I also cleaned the tb and all of the sensors

 

FWIW I don't think that's a valid test, when the IAC is unplugged it just holds it's current position, so there won't be any change. Does sound like it might be sticking though.

 

Could also be a TPS going south.

You've done the sensor ground test and ground refreshing, right?

 

This is exactly what mine has been doing. I tightened the manifold bolts and right away it was 100% better. After a few days though it was back. I will be trying the TPS this weekend.

 

I'll be testing all sorts of stuff Sunday, now that my brother has his garage cleaned out enough to pull a vehicle inside so, we don't freeze our butts off.

I'll pull the IAC valve to see if it's gummed up with carbon (I've had to clean it once already, a year or so ago). If not that, I'll test the TPS and recheck all my vacuum hoses. I recently replaced my water pump and it started acting up shortly after that but, I made sure all the vacuum hoses were back in place (had to pull the air filter box to give me enough room to remove the P/S pump and bracket.). I may even test the O2 sensor to make sure it's reading correctly.

I'm not getting a check engine light which is why I'm sorta stumped on what it could be.

 

Our Renix jeeps do not have CELs. The system does not store codes.

I'm gonna go ahead and guess that your issue has nothing to do with the TB being dirty. I say this because mine is spotless and I have the same exact problem. Not that cleaning the TB is a waste of time

 

Hey Hamster. Happy new year! (btw). That has been a reoccurring issue with my 90. Are you fimiliar with the old idle speed screw on a carburetor? The Idle Air Control replaces that, a computer controlled "throttle plate leak".

Do make sure there is some, (almost ZERO), play in the trans kick-down cable. That could hold the throttle if it were somehow tight. Be really careful with cleaning the IAC. Squirt the screws a day ahead with PB, be sure you have the correct torx driver, make sure you have the O ring on right. Just because they are small screws doesn't mean you will not be pissed if they break. (they ARE thankfully soft, and relatively easy to drill out)

Do you ever feel a "catch" accelerating? There is a brittle little shroud/tube around your throttle cable between the pivot business and the business. I found mine just crumbled when squeezed with lineman's pliers. Problem solved, but the problem was "catching" on acceleration.

 

I'll check the kickdown cable.

As I stated above, I've cleaned the IAC once already so, the screws have been removed before with no trouble.

I've never noticed any "catching". My throttle has always been smooth and easy to move.

What about the emission maintenance timer? Can that negatively affect my engine performance (or does it simply turn on the light every 80k miles)? I've read posts on other forums of people simply unplugging it and throwing it away.

 

It just turns on the light at a preset interval, it doesn't do anything else.

 

I just remembered. When mine does that I turn it off, then start up again. At least once I needed to do that at least twice. (This is after cleaning the IAC twice). It's so rare I haven't changed my IAC. Just for fun, maybe check/clean the connections on your Latch relay, (#3). I believe part of it's function is to provide power for a bit after shut-down so the IAC can re-set for cold start-up. I don't know if it can affect normal function, but cleaning it's contacts is no big deal. Heck, swap it with #4, the AC clutch.

You don't have a check engine light!

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.

 

I'll be sure to check all that stuff.
As far as the injectors go though, they are all new. I put all new injectors in, summer of 2012.

 

You have done my basic Renix Tips already, haven't you?

 

At the top of this link, is a link for 02 testing for Renix>
https://www.cherokeeforum.com/f2/ren...ce-rms-133153/

Pictures of testing injectors> Post #85.
https://www.cherokeeforum.com/f2/199...r-swap-163105/

You might make sure the line to your Fuel Pressure Regulator is not wet inside. Were that diaphragm to fial, (a hole in it), it would suck fuel into the intake manifold.

 

Pulled the IAC.........looked good. Sprayed all vacuum lines that I could get to and nothing........no problem found. Checked all electrical connectors to make sure none got unplugged during the water pump replacement and all were good.

I did the battery cables and ground wire swap last year so all those are still good.
The only thing I didn't get a chance to do, was to test the O2 sensor and wiring.
I'm not sure why or what exactly happened but, I did notice a slight change on the drive home. It still idled high but, not as high as before and for not as long. I'll keep an eye on it over the next few days and see how it does.