1987 Renix High Idle Issue

[NicksRenix04]

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.
Thank you!

 

[Saudade]

Welcome!! It's great to hear you're committed to getting the ol' XJ in tip top running shape. Perhaps we should all be committed!

I have an '88.

A few things. Sounds like you do have a vacuum leak. The one "behind the TPS", may be a worn shaft on the throttle shaft. Check out this video for clues and, if you determine that's it, how to fix it. One trick it to spray some starter fluid at the shaft, or use an UNLIT propane torch and douse that area with propane. If the idle drops, then that would indicate the leak is there. (Did I say unlit?)

Next, you mention the EGR. These are tricky little buggers. Do you have the transducer connected? Looks like a small saucer shaper plastic disk with 3 vacuum connections. Your EGR valve itself should have 2. The EGR looks like this:




This is the one in my '88. So the vac line from the solenoid next to the ballast resistor goes into the transducer, then the transducer connects to the EGR valve. Not sure it would contribute to a high idle, but can still cause some funky idle if it's not sealing properly. You can remove the egr valve and clean the ports if needed.




When mine sits for a day or so (not a DD) and I go to start it, mine will also jump to a high idle at first, but then come back down to normal. When I first start it, I can hear the vents doors moving. If I shut down and restart (or restart an hour or so later) it goes to proper idle right away. I'm sure mine is due to loosing vacuum in the reservoir (located behind the front bumper) over time and the initial start results in sucking the air out if the HVAC system resulting in the momentary high idle. So are your vent doors working OK? Does it blow air out the right vents based on the setting on the HVAC control?

Cruiser54 is no longer with us (RIP) but there are a bunch of us RENIX guys still around. Glad you got the Nickintime monitor. He's been OOS for quite a while now.

 

[NicksRenix04]

Welcome!! It's great to hear you're committed to getting the ol' XJ in tip top running shape. Perhaps we should all be committed!

I have an '88.

A few things. Sounds like you do have a vacuum leak. The one "behind the TPS", may be a worn shaft on the throttle shaft. Check out this video for clues and, if you determine that's it, how to fix it. One trick it to spray some starter fluid at the shaft, or use an UNLIT propane torch and douse that area with propane. If the idle drops, then that would indicate the leak is there. (Did I say unlit?)

Next, you mention the EGR. These are tricky little buggers. Do you have the transducer connected? Looks like a small saucer shaper plastic disk with 3 vacuum connections. Your EGR valve itself should have 2. The EGR looks like this:

View attachment 12006


This is the one in my '88. So the vac line from the solenoid next to the ballast resistor goes into the transducer, then the transducer connects to the EGR valve. Not sure it would contribute to a high idle, but can still cause some funky idle if it's not sealing properly. You can remove the egr valve and clean the ports if needed.

View attachment 12007


When mine sits for a day or so (not a DD) and I go to start it, mine will also jump to a high idle at first, but then come back down to normal. When I first start it, I can hear the vents doors moving. If I shut down and restart (or restart an hour or so later) it goes to proper idle right away. I'm sure mine is due to loosing vacuum in the reservoir (located behind the front bumper) over time and the initial start results in sucking the air out if the HVAC system resulting in the momentary high idle. So are your vent doors working OK? Does it blow air out the right vents based on the setting on the HVAC control?

Cruiser54 is no longer with us (RIP) but there are a bunch of us RENIX guys still around. Glad you got the Nickintime monitor. He's been OOS for quite a while now.

Thanks for the warm welcome! Looks like you're here in SoCal too! Thank you for the information regarding the worn throttle shaft, I think thats a good possibility. With the help of a friend, I've been able to determine that at a minimum, my EGR diaphragm is not working. My EGR does not open nor close with vacuum (mouth tested with a rubber hose). So it will need to be replaced regardless. My EGR, does not have the UFO transducer-looking thingy. However, I have located a used & hopefully working EGR through a friend (it has the transducer and looks more like yours). Funny enough, I had a vacuum problem with the HVAC (only blowing out of defrosters), two of the lines going to that vacuum canister were broken, but patching those seems to have fixed my vents. It seems to hold vacuum for a while, haven't tested how long. I talked to Cruiser a few weeks ago regarding Injectors, the news hit hard.. I'm sure he's living it up with the Renix gods up above. I'm guessing that if the EGR doesn't do it, then the throttle shaft will be the next place for me to look.

 

[tjmotter]

Grab a wrench and check to make sure the intake manifold bolts haven't backed off. My '90 had a high idle problem that took me months to track down. Seems the original bolts had worn to the point where they could wiggle loose after a couple of hundred miles. I had to regularly tighten them and eventually, ordered a new set of bolts from NAPA and replaced them all. No issues since.

 

[NicksRenix04]

Grab a wrench and check to make sure the intake manifold bolts haven't backed off. My '90 had a high idle problem that took me months to track down. Seems the original bolts had worn to the point where they could wiggle loose after a couple of hundred miles. I had to regularly tighten them and eventually, ordered a new set of bolts from NAPA and replaced them all. No issues since.

Thanks for the suggestion. I will double-check them when I replace the lower portion of my Airbox. I think I'm onto something with my EGR vacuum leak. I will keep the thread updated.

 

[NicksRenix04]

Well, the new EGR didn't do it. Did another smoke test, this time into the brake booster line rather than the throttle body boot, and the vacuum leak at the throttle body shaft has just about disappeared (might have been getting a false positive there when injecting the smoke into the throttle body boot, I'm thinking the smoke was building up pressure at the TB butterfly, and therefore leaking anywhere it normally wouldnt), and the leak at the new EGR is minimal, probably an amount that one may expect. Still Idling in Park/Neutral at around 1100RPM, and in Drive around 800. With the Jeep warmed up, I can see the pintle/reed in the EGR moving when giving the Engine a good rev, so I'm pretty sure it's working. Running out of ideas...

 

[Saudade]

At least your egr works now.

So you can get a can of starter fluid or an UNLIT propane torch and spray the fluid/gas around the intake manifold, TB, FPR, air box, the vacuum harness junction, etc., and see if the idle changes. Don't firehose it with starter fluid, just a few quick spurts at each place. If there's a vacuum leak, it will suck in the fluid instead of air and the idle should drop momentarily. Same for for the propane but you can leave it on (did I say UNLIT!!). Same principle applies.

Or you can just start disconnecting and capping the vac lines not needed to run the engine. Cap the EGR off at the solenoid. Cap the vac port on the intake for the HVAC. Plug the line that goes to the top of the airbox. Cap/plug the brake booster line. and so on.

Double check your TPS adjustment. On my '88 I had to deviate from the spec to get mine to idle. You might have to as well, but first verify you have no vacuum leaks.

 

[NicksRenix04]

At least your egr works now.

So you can get a can of starter fluid or an UNLIT propane torch and spray the fluid/gas around the intake manifold, TB, FPR, air box, the vacuum harness junction, etc., and see if the idle changes. Don't firehose it with starter fluid, just a few quick spurts at each place. If there's a vacuum leak, it will suck in the fluid instead of air and the idle should drop momentarily. Same for for the propane but you can leave it on (did I say UNLIT!!). Same principle applies.

Or you can just start disconnecting and capping the vac lines not needed to run the engine. Cap the EGR off at the solenoid. Cap the vac port on the intake for the HVAC. Plug the line that goes to the top of the airbox. Cap/plug the brake booster line. and so on.

Double check your TPS adjustment. On my '88 I had to deviate from the spec to get mine to idle. You might have to as well, but first verify you have no vacuum leaks.

I opted to try the latter test. I unplugged many vacuum lines and plugged them with some Torx bits. In particular: The vacuum source that goes to the EGR solenoid, the hose on the intake that goes all the way to the vacuum ball, the brake booster line, as well as the vacuum source for the bi-metal temp sensor in the airbox. I ran the engine with all of them plugged, and there's no difference, still idles high around/above 1000. According to my REM, the TPS is at 17%, so it's correct. Whatever the issue is, it stays consistent. I can count on it to act the same way tomorrow. The engine starts up around 700rpm cold, then as it warms up, the RPM lopes/fluctuates consistently until it reaches around 1000-1100. Once it reaches that threshold, it continues to lope and cycle back and forth between 1000-1100. Rather, when in drive, it doesn't lope/cycle, and stays rock solid at about 800RPM.

 

[90xj06]

maybe check and clean the IAC its next to the tps sensor. it might be stuck or not working. that's what actually adjusts the idle.

 

[NicksRenix04]

maybe check and clean the IAC its next to the tps sensor. it might be stuck or not working. that's what actually adjusts the idle.

Thanks for the suggestion, IAC is clean and not dirty, as I thoroughly cleaned the TB last week. On my REM, I can see the IAC drop from about 130 to 0 throughout the course of warm-up.