hgeranium

And yet I wouldn't trade it for anything else. Stockholm syndrome?

I feel like I've been posting way too much. One problem fixed creates two more problems. When removing my TB to replace the gasket, I took off this throttle link (pic isn't mine) from the bottom end (I couldn't get the top to come off and was worried about breaking it). When putting everything back together, that bottom ball end would no longer seat securely on the ball. There was already a ton of play in the link when it was connected so it was already very worn out. I ended up having to tape the link to the lever to get home. My question is: What is the right way to remove the link and install the new one? The bottom end is no problem, but I didn't have any luck with the top, unless there's a specific method that I'm not aware of. I am fine with breaking the plastic end but still don't know for sure how to install the new one. Will the metal ball just pop into the joint with enough pressure? I like knowing exactly what to do/expect when possible so the job goes smooth.

Alright guys, I made a thread previously about this issue, thought snugging up the manifold bolts fixed the problem, but it has returned in full force. I am going to go into much more detail because, at this point, I am at a total loss for what could be causing this high rev issue. I apologize for the length, I figured the more detail the better. The issue plays out like this: I start the truck, the revs shoot up immediately to 2000-2300 and stay there. Putting the truck in a gear drops the idle (like usual) to a cool 1500-1700RPM when completely still. The truck always wants to lurch forward when it is in this state, it is especially scary when in traffic because the revs are fighting the brakes and they're barely enough to keep the truck stopped. It feels like I have my feet on the gas and the brake at the same time. When I turn the truck off in this state, it shuts off hard and shakes the entire thing having to abruptly stop the motor, which can't be healthy for it. For this reason, one of my suspicions is that the throttle plate is getting partially stuck open. This makes sense logically as to explain my symptoms but I am more at a loss of what could be causing it. The most difficult part is it's intermittent. I find that, rather than it differing from startup to startup, the problem can persist for a full day or two and go back to normal for however long. Turning it off and back on does not fix the issue in most cases. I have had instances where the increased idle occurs for 10 seconds, 30 seconds, 1 minute, 5 minutes, and the entire length of every trip I've taken throughout a day (20-30 minutes driving total). The added inconsistency to the already intermittent nature is making it very frustrating. In the cases where the problem resolves itself, I see the revs crawl back down to a normal state and it drives perfectly fine afterwards. Even in cases where the revs don't get up to the 2000s, I've seen my idle in park hang out around 1200-1400 and my idle in a gear is right at 1000. This is much easier to deal with when trying to drive because I'm not fighting the truck to stop/slow down nearly as much, but I know it is the same issue occurring at a lower intensity. This also makes me think it could be some vacuum issue in the manifold gasket itself? If there's not a full seal, it makes sense that extra air would get sucked in and raise the idle, with the problem fixing itself in the rare cases that the leak gets a good enough seal to vacuum it off. All my other vacuum lines are good (tested with brake cleaner, no change in idle), but I haven't gotten around to checking the manifold gasket with brake cleaner/water since I'm writing this not long after it happened. It's on my to-do list when I have a morning off. Relating to this ^ are there any tips/how to for removing the manifold heat shield? I don't want to have to mess with the injectors/fuel rail to get it off, but I don't see another way nor do I see any guides online. I'm going to list related or adjacent fixes or checks that I have done pertaining to the idle so y'all know what has been done and not worked: New TPS (voltage tested), new IACV, cleaned throttle body (not taken off and fully deep cleaned; I have the gasket and is on my to-do list) and sea foam treatment, manifold bolts all snugged down (top of gasket vacuum tested w/ BC but not the bottom yet). It may not be related but all my sensor grounds are good, no resistance anywhere (cruiser tip 5). I remember since I've owned the truck from 2022, this problem was a once-a-month (if that) occurrence, but in the past few months, seemingly out of nowhere, the issue has become exponentially more common and severe (multiple days a week, multiple times a day). This few week period between my original post and this post is the longest I've gone without the throttle sticking once in a good few months. I have a satellite "issue" where, even if it idles normal on startup, it'll still rev up to the 2000s and come right back down. I am willing to bet that the cause for the high idle is also causing this issue. The amount it goes up is inconsistent and sounds different every time, so it seems more of an issue rather than a quirk. When neither of these issues occur, then at cold start, the RPMs will go up a normal amount and come down fast enough to kill the motor if I don't blip the throttle. This happens in all seasons, doesn't matter if it's cold outside, just the engine being cold. That's all I have right now. I am going to start recording every startup to capture some evidence and add onto this thread with those along with any attempts at repairs. I will be happy to share any more details if needed. TL;DR: Throttle stuck open on startup intermittently, I'm thinking either there is an intermittent vacuum leak in the manifold gasket or the throttle plate itself is getting stuck open.

Are you 100% sure that it’s the computer? A 4.0 has many causes for the symptoms that you’ve explained. You can buy reman ECUs from any big box retail or online store, or preferably grab one from a junkyard. There should be a few years that have the same ECU that you need; someone smarter than me can tell you.

Thanks for the graphic! When tightening my bolts I just used a picture of a manifold gasket and referenced the holes on the bottom I needed to find with the top holes lol

After some independent research I did see something about slower logic from the ECU means it takes longer to verify crank position, so I'm sure you're right.

Great to know! It makes me feel better knowing it's a 'quirk' of the renixes rather than something I need to diagnose. Thank you

I wanted to get a little survey on how long it takes to turn your XJ/MJ over when cold and warmed up. My MJ has consistently taken 7 to 10 cranks cold, and 5-8 when warmed up. This is the oldest vehicle that I've owned (2nd oldest is a 94 GMC C1500), so I'm curious if it's just a 4.0 being a 4.0. It's not like the truck has trouble starting up, just more cranks than I would be expecting. I feel like I've seen online people starting up their XJs with 3-5 cranks. My GMC always started up quickly, but I suspect the TBI played a part in it. My only in-person friend with an XJ has a chevy 3.4 swap, so I don't have any IRL comparisons to make.

I agree with eagle on the manifold bolts. I made a post a few weeks ago about an intermittent high idle/rev on startup (eagle might have been the one to tell me to check it), and I tightened all the bottom manifold bolts that needed to be snugged. I'll never actually know if the problem is gone, only if it comes back, but as of now my startups have been much smoother and less aggressive.

My friend spotted this jeep back in San Antonio! Looks quite different to that auction picture.

Thank you very much! I’ve read about that happening to people but stupidly never checked myself.

An occurrence that has been happening for almost as long as I've had this MJ, about 3 years now, (88 4.0 AW4) is that, on occasion, during cold starts (sometimes when warmed up too, but more seldom) the motor will rev up hard to ~2000-2200 for a few seconds and come back down. I also had another issue paired with that where the revs would go up and get stuck there, even while driving. This happened seldomly through the last 3 years but really ramped up last month. The throttle would get stuck open. Super jumpy, hard to brake, etc. like the throttle plate was cracked open. I cleaned the TB (no major carbon deposits), ran a can of sea foam, and replaced the IACV a few weeks ago and I haven't seen this problem come back thus far. However, even with the throttle body cleaning and IACV replacement, that high revving phenomena still regularly occurs. I guess I would like to know if this a common occurrence for anyone else and I should just ignore it as an old vehicle quirk. It is my daily driver, so that's why it's more of a concern to me than if it were just a project. TPS is brand new, voltage tested perfect and within that specified resistance range (Cruiser tip #8). Vacuum lines are solid all around, no leaks there. Resetting the IACV does nothing to change it. The truck runs flawlessly other than that. In park it idles steady at around 900rpm and in drive stays steady at ~700. The fact that the truck runs so well otherwise leads me to believe that it's just an old vehicle quirk but wanted to run it by y'all with much more 4.0 experience than I. Thank you!

Not sure how appropriate this is considering it's not a cruiser-appointed tip, but a very quick DIY fix that eliminated a great bit of my wind noise is found in this old BleepinJeep video: All you do is stick a line of 1/4" poly rope between the door seals and the frame itself. It puffs just enough to seal up any gaps. This also helped stop a leak from the top of the doors during heavy rains or when washing the truck for me. Another thing that is well documented for MJs/XJs with the older style metal trim around the front windshield is to swap it out for the rubber one piece molding when replacing the windshield. I'm sure that none of this is new for many of us but I figured it's better to have something than nothing in regards to the tips that cruiser never got around to writing up. Hopefully any lurkers browsing cruiser's tips on the forum will find this helpful.

What was your price on that? I was planning on using a six foot tarp with magnets along the bed, but that is a much better idea!

Ah, that’s unfortunate to hear. Some junkyard vent window assemblies will have to do, then.

Woah! Good find!

1988 Jeep Comanche Eliminator 4.0, AW4, 4x2, D35 rear, SWB Build date: n/a, that door sticker is long gone.. South Texas Bought it in 2022 with 176k on it. As of 8/2025 I have put just over 10,000 miles on it. I daily drove it all of 2022, had a second car from 2023-early 2025 so drove the jeep less frequently. As of March 2025, it is my one and only daily driver again! This is my first Jeep, being heavily inspired by my good friend who has an engine swapped 1984 Cherokee Chief. I happened to come across it on marketplace only a day after my previous truck was totaled in front of the house by a texting driver. It runs and drives fantastic, I frequently have to make ~400 mile round trips and never get any complaints from it.

Both of my vent windows have now suffered the same fate of that bottom rivet, specifically that black rod, connecting the window to the door completely rusting out and breaking in half. I'm wondering if anyone has any experience with a DIY fix without fabricating/rebuilding that mounting? Or would a full window replacement be the best way to go otherwise? Attached isn't my picture. No AC or vent windows in the Texas summer is going to get old quite fast, so I'm willing to try even the jankiest fixes. My jeep has had its fair share of them.