• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

1987 Renix High Idle Issue

It just adjusts the amount of air through the throttle body independent of the butterfly and IAC position...you should be able to tighten it and see the idle drop. Set it to what you want. Based on my XJ, I'd recommend around 600 in gear which will be around 750 in neutral. Below that, my alternator drops under 12v
 
It just adjusts the amount of air through the throttle body independent of the butterfly and IAC position...you should be able to tighten it and see the idle drop. Set it to what you want. Based on my XJ, I'd recommend around 600 in gear which will be around 750 in neutral. Below that, my alternator drops under 12v
Thank you! Think I should adjust it when everything is warm? Or cold? I'll use a paint pen to mark the current location so I know where to reset things if need be. I'll give it a shot tomorrow
 
Probably warm, but I haven't done this and haven't found anything about it in the FSM so I don't really know.
 
Unfortunately my starter went out yesterday, so I replaced it this morning before going to work (much quieter!!!). Haven't had time to mess with the idle bleed screw, however I remember that last time I covered the idle bleed hole on the top of the TB, it made little or no difference in the idle.
 
So I marked the current location of the idle air bleed screw with a paint pen, and I tried tightening it during high idle. It tightened about 3/4 of a turn before it stopped (fully closed). There was no noticable change in the idle. So I loosened the bleed screw 3/4 turn back to its original position. Clearly air is still getting in somewhere?

Vacuum line assemblies are new, ccv grommet and line are new, myself; as well as a smog shop smoke tested it to no avail, Intake gasket is new and bolts are tightened to spec, TB gasket is new, different EGR tested, I've plugged all the vacuum lines going to the intake while running (no change), and replaced IAC. All made no progress or difference.

The sign that still points me to some sort of a vacuum leak is that if I cover the IAC port on top of the TB when the jeep is idling cold, it stumbles and tries to stall, but when hot, covering the hole makes no changes.

I think the only thing I really have left to blame is the throttle body? Anything else?
 
Another thing that just confuses me to no end is the fact that the Jeep idles PERFECTLY, in gear. Between 750-800, even when warm. But the second that the shifter goes into Park or Neutral, it rises to 1000. When cold, the Jeep idles close to 750 in park, but it slowly rises as it warms up.
 
I see about a 150RPM difference between drive/neutral but 200 doesn't seem insane to me. In drive there's just more load on the engine from spinning the torque converter with the same amount of fuel and air - naturally the RPM drops.

I'd try capping the EGR to completely eliminate that, and check that the intake manifold ports are all tight (IAT, vacuum port tree, etc)? Any chance the rear valve cover grommet for the PCV line was drilled out at some point in the past?
 
I see about a 150RPM difference between drive/neutral but 200 doesn't seem insane to me. In drive there's just more load on the engine from spinning the torque converter with the same amount of fuel and air - naturally the RPM drops.

I'd try capping the EGR to completely eliminate that, and check that the intake manifold ports are all tight (IAT, vacuum port tree, etc)? Any chance the rear valve cover grommet for the PCV line was drilled out at some point in the past?
The RPM difference doesn't sound like a lot but it is very noticable when shifting from Park to Reverse. Very very hard slam. No slam when the jeep is idling normally while cold. I like the idea of checking all the threaded vacuum ports in the intake, I'll check them tomorrow. Also, you're recommending me to cap the EGR's vacuum line? I replaced the CCV grommet with the proper grommet and also replaced it's line that goes into the intake.
 
I checked all the fittings that thread into the throttle body. All are tight. Air is getting in somewhere?? Since covering the IAC hole doesn't drop the idle when it warms up..
 
So I got home from school not too long ago, and since the Jeep was nice and warm from the ride home. I decided to do some more quick tests. I removed the throttle body-to-airbox boot and started the Jeep. The thing idled perfectly around 750-800 for maybe 5-10 seconds, then it went back to idling high around 1000. I put my thumb over the IAC hole, no lowering in the idle. I also tried covering the bleed-hole, and that seemed to lower the RPM by 50 or so. It seems that the majority of the air is going through the butterfly and the bleed hole (hissing can be heard from the bleed hole), with a minimal amount through the IAC hole . When I was all done, I reinstalled the throttle body-to-airbox boot and started the Jeep back up. It immediately went back to idling around 1000. Very strange behavior. I am considering purchasing another throttle body to test. The EGR plate is still on my mind however I've already tried 2 different EGRs.
 
That would explain why the IAC is closing - the ECU is trying to lower the idle but can't lower past fully closed. Maybe the bore is just worn from butterfly movement?
I can see the IAC drop from about 130 to 0
 
That would explain why the IAC is closing - the ECU is trying to lower the idle but can't lower past fully closed. Maybe the bore is just worn from butterfly movement?
I was possibly thinking this, or maybe throttle shaft seals. Although I find it a bit strange for them to be worn down enough at only 150k miles. But I guess anything is possible. When I cleaned the throttle body for the first time back in 2023, it looked like it hadn't ever been cleaned before. I took some pictures of the TB yesterday and it does look a little like the butterfly could be wearing the right side of the bore, in fact, it looks a teensy bit off center. Im going to have to upload some pictures via my computer.
 
I was possibly thinking this, or maybe throttle shaft seals. Although I find it a bit strange for them to be worn down enough at only 150k miles. But I guess anything is possible. When I cleaned the throttle body for the first time back in 2023, it looked like it hadn't ever been cleaned before. I took some pictures of the TB yesterday and it does look a little like the butterfly could be wearing the right side of the bore, in fact, it looks a teensy bit off center. Im going to have to upload some pictures via my computer.
I can't seem to upload the photos directly to the site from my computer, so I've compiled them into a little google doc. Hopefully, it's good enough. I did take some pictures a while back of how dirty my throttle body was. In those pictures, on the right side of the throttle body, a clean and shiny mark can be seen in the bore and on the edge of the butterfly. So it definitely looks like the butterfly is contacting the bore. In the fresh and clean photos I took yesterday, you can see some very thin gaps on the left side of the butterfly. I am not sure if all this points to wear, or if someone has tampered with it.

Hopefully, this link works..
 
I got some vacuum caps at Napa this morning. I plugged every unnecessary vacuum line going into the intake manifold. The only ones I left connected was the vacuum line for the fuel pressure regulator, Map sensor, and CCV. This means that I capped off the brake booster line, the EGR diaphragm line, EGR solenoid line, and this one line at the back of the manifold thats next to the IAT. Still idles around 1000 in P/N.

I found someone relatively locally who has an entire Renix manifold, complete with fuel rail, injectors, throttle body w/ IAC+TPS+IAT, and EGR for a very very good price. So I'm thinking I'll try and get it, mainly for the throttle body.
 
Seems I recall that the c101 connector can come into play with high idle.
 
Back
Top