Hi Folks, I'm new here. I'm 19, and I inherited my Grandpa's 1987 Renix Wagoneer about a year ago. Since then, I've learned a LOT about cars and it's been a fairly reliable daily driver since roughly last August. Now that most of the major things are ironed out on the thing, I'm slowly improving it and bettering the small things, such as dash rattles, interior, etc. One of the things I'm working on currently is its high idle that's driving me nuts! The idle isn't crazy high, but it's more than it should be. In Park and Neutral, its running about 1100RPM fully warmed up, and in Drive/Reverse it runs fantastically at about 8-850RPM fully warm. When I start the Jeep cold, it may surge to about 1100, then quickly make its way down to about 6-700ish. Throughout warming up, the Idle will lope and eventually make its way up to around 1k-1100RPM. I have no serious drivability issues though, and the thing never skips a beat. No random surges or drops, when warm It just lopes consistently around 1k-1100RPM in Park and Neutral when warmed up. If I turn the car off, and back on, it goes straight back to idling where it was, no funky ' idle resetting' or anything like that. The problem is consistent and I can count on it to do the exact same thing each day.

Some things I've replaced/ or done that may be relevant to the issue include:
-Replaced 2 main Vacuum Harnesses
-Replaced PCV grommet and line
-Replaced CPS & properly adjusted it (from Napa)
-Replaced TPS (from Napa) (Ground checked, around an ohm)
- New 195Tstat (Napa)
-Replaced 02 Sensor (Bosch 12009, great 0-5v swing on REM)
-Cleaned Throttle body & replaced gasket (stop screw doesn't seem to have been tampered with, gap between bore and butterfly is .003", left it alone)
- Replaced injectors with Bosch 823 Injectors & new O-rings
-Did Cruiser54's Tip 31, permanent Map line fix
-Snugged Intake bolts
-Thoroughly cleaned C101 (When I say thoroughly, I spent over 2hrs cleaning it)
-Reset the ECU (I know it doesn't store codes, but I've heard it stores fuel trim)
-Cleaned major grounds in engine bay
-New Fuel Filter, properly gapped plugs (.035), rotor, cap, and plug wires

I also did a vacuum leak test. I got one of those EVAP smoke testers from Amazon. I discovered a few Vacuum leaks.
-Two at the lower part of the airbox (cracked airbox, new one has been found, don't have it yet)
-One at the Map line Grommet (has since been fixed thanks to Cruiser's tip)
-One at the TPS? (looks like its coming from behind the TPS? IAC has a new O-ring.)
-One huge one at the EGR. (I did some poking, and the leak is NOT coming from the diaphragm part of the EGR where the vacuum line connects)

My main hobby besides working my Jeep is fixing old tube radios, so I know my way around a multimeter if need be. I also have a Renix Engine Monitor, if anyone would like some of the Data from that, I can provide it. I hope some of the knowledgeable people here can help guide my young soul in fixing this strange problem. I also posted this in the NAXJA forum, never hurts to try and reach as much input as possible!
Thank you!

 

Sounds like a very desirable Jeep Nick. I hope you kept the TPS that you removed, especially if it was MOPAR and still functioning. Your vacuum leak at the EGR needs to be figured out and resolved. I'd be curious to see what you have for Ohms if you back probe the "B" terminal of the TPS connector to the negative on the battery.

 

Ha! I've had plenty of people want to buy it from me, I don't think any amount of $$ could get rid of it right now, probably cause I have more in it than its worth LOL. I'll see if I can attach a picture of the smoke test I did with the EGR, Even with the vacuum line unplugged it'll pour smoke. I'm reading about 1.8 ohms to ground from the TPS connector. Might not hurt to splice in a supplementary ground wire. Also, yes, I kept the old TPS.

 

1.8 Ohms is pretty good. Does it remain constant if you agitate the wiring harness alongside the head and behind the engine? Don't add a ground to the sensor circuit. It gets its ground from the ECU (see attached diagram (highlighted in yellow)). I'd say your slightly high idle is most likely caused by that vacuum leak.

 

Alrighty, kinda what I'm suspecting as well. I take it that the vacuum leak at my EGR probably means that it is bad right? If so, I'll have to source a replacement since I live in SoCal. I imagine it being bad could also be the reason for my poor mileage. I'm managing about 9.5mpg around town. Also, yes, the resistance remains constant, I wiggled the harness around at various points, and no noticeable changes.

 

I responded to your post in another forum. Is yours a 6cyl or 4cyl? I assumed it was 6. If 6, then that's not the right EGR. That looks like it's for a 4cyl. Not that it won't work, just be aware if you look up any other info about it. The proper EGRs for the 6cyl are pretty much non existent. As for the smoke, where did you inject the smoke? There's a pintle in the EGR that opens when vacuum is applied to allow exhaust to enter the intake to reduce emissions. You shouldn't get any smoke around there. You can remove the EGR, clean the pintle and try a new gasket.

Have you passed smog check?

 

Darn! I should have clarified. I got the 4.0. I injected the smoke through the throttle body boot on top. The Amazon smoke kit I got has a big rubber cone that fits it. I haven't removed the EGR yet, but will to replace it. I did pass smog believe it or not. I still cant believe it either. Since the Jeep was a family transfer, I guess they only had to do half of the full test on it? I was sweating bullets in the waiting room when the smog guy was revving it up.

 

My 90 renix had a vacumn leak at the egr valve and also had a 1100 or so idle when warm. The egr is unobtainable so I made a aluminium plate to put over the egr port. The egr is still plugged in and bolted back on so it would pass the visual check .
Mine is smog exempt so I don't know if it would pass smog or not.
Mileage wise after I got things straightened out with the REM , I've been getting 14 city and usually 18-19 highway with stock gearing and 235-75-15s.
74Plb

 

Interesting. Well, I hope that this is the smoking gun that fixes the problem. Unfortunately, I cannot block the EGR since California has Smog. Did you notice any mileage improvements after fixing the vacuum leak at your EGR? I'm getting about 9.5mpg around town, everything on mine is stock too.
I've got a used EGR sourced from someone who lives in a non-Smog state, hopefully, it'll get the job done. I will keep the thread updated.

 

Here in CA. the inspectors are required to do both a visual and function test of the egr. Now, not every place is as thorough as the one I use.

The one he has on, appears to be from the 4 cyl and also appear to be readily available. I've seen some others use this instead with no drivability issues. I highly doubt any current smog inspector would know the difference as long as it worked (functionally an NOx within limits).

 

I live in Washington state on the border of Oregon. Not sure if a 34 yo vehicle still needs a smog check in Oregon or not.
When I bought my XJ in 2020 it was running in open loop and got terrible mileage. After changing the O2 sensor the mileage came up. I don't recall a big jump after plugging the vacumn leak up at the Egr.
I had a 2 year old XJ 1989 Xj back in 91 and the best I ever did on that was 20 mpg on the highway. I'm thinking the 19 I'm getting now isn't too bad.
74Plb

 

Interesting I guess I should count my lucky stars that I passed. I pulled the EGR for kicks and giggles and hooked my smoke machine to the port that goes to the intake. It looks like smoke is leaking out of the area where the piston that connects to the diaphragm goes into the base of the EGR (marked in red), I guess the seal there is compromised or something. Anyways, I put it back on till the replacement arrives.

 

Well, I got the proper EGR in, and did another smoke vacuum leak test on it. It also appears to have a vacuum leak in the same spot, like the old one. I wonder if it's normal for them to give false positives when under pressure from the smoke tester? The only change I see in the Idle is that it's about 50rpm lower in Drive (used to be around 850, now its 800), still too high at 1100rpm in Park/Neutral. Not sure what my next course of action should be..

 

I may be getting a false positive when I inject the smoke machine at the throttle body boot. When Injected at the brake booster line, the EGR leak decreases drastically, as well as the throttle body shaft leak. Leaks are minimal enough that I don't understand what else it could be.

 

At what point did the high idle start? Is that the way it was when you received it, or did it start after you started doing some maintenance and replacing parts?