AnotherOldJeepGuy

I see this type in some videos, the corrugated area seems to make sense to me, anyone using this type? Opinions?

Thanks, that's pretty good. I watched another one where they left the injectors in place but it was I think a 97 so it was similar but not exactly right.

Me too. I have started looking for good youtube videos on how to replace it.

More hunting no finding. I dosed it with water from the top and from the bottom, up in from the front and then from both sides, no noticeable change. Even with the new muffler it is still loud, very throaty, ahead of the muffler, somewhere. So it seems less and less likely this is a tighten something fix. So the ugly things I can think of are blown manifold gasket, cracked intake manifold, cracked exhaust manifold. I know the gasket is available, but if I screwed up either of the manifolds, are these things available anyplace other than the local junk yard that may or may not have one, or have a good one?

I would be glad to have a member volunteer to help! The last time I saw a Comanche other than mine in the wild around here has been quite a while. Years not months or weeks! But if there is someone around Plano TX, I'll welcome the help!

So, new muffler, which there was no doubt a need for since the old one was no longer connected. But, no change. If there was any doubt that it was a vacuum leak, I don't think there is now. I turned on the AC coming back from getting the muffler and 90% of the wind was coming out the defrost. I have patched the small line just outside the firewall that provides vacuum to the airflow control when this happens more than once. But that's a very small line and when it comes apart it doesn't have any noticeable effect on the engine, too small I assume, it just eliminated the airflow control until I patch it. Besides, I don't see any broken spot there now. I pulled off the line to the brake booster while idling and there was a lot of vacuum there for the few seconds the truck ran before stalling. No idea of any "number" to put on it, but there was plenty of air being sucked in. So there is a leak, I just can't hear it or find it. I'll be trying the water again once it cools down, and maybe I'll notice something now that it's a bit more quite with the new muffler, but I doubt it.

Well Midas says they won't honor my warranty! That sucks. But the muffler still needs fixed so I am going to the local muffler shop instead. I did take a shot at AI and asked if the broken pipe would cause vacuum issue, since my interpretation was that if the bolts at the manifold end being loose could, then an open pipe at the other end would cause the same thing. AI says it will NOT! Bummer, I am less optimistic now my full issue will be fixed by fixing this.

VIN Decoder says this, if that is helpful..

Heading to Midas sometime today, will post back if this restores my smooth idle...

I was thinking it was #24 because it has a round edge, and there's a hole in it where I assumed the started was inserted. But I do note if the picture is top/bottom correct, #22 would be the one at the bottom. Hmm. Anyhoo, I need to resolve my "Mayday" post before worrying about this...

I am cautiously optimistic I found my problem. It never occurred to me that a broken pipe at the muffler would cause the engine to idle rough, to stall, or to cause the power brakes to no longer be powered, but now that I see it, this pipe does go directly up to the engine where the suspicious bolts that tend to work loose are. Pipe broken loose from front of muffler. My muffler has been shot (from a sound perspective) for quite a while which is why I didn't really look here first just from the sound. If I am lucky I can even get this fixed for free, but I won't hold my breath. I bought this muffler from Midas about 20 years ago and I purchased the lifetime warranty. But, when I went to Midas a year ago to ask for a new one the desk person said "Lifetime warranty, we don't do that". So it may be a loosing battle getting it replaced under warranty. But if this revives my truck I am happy to pay for a new muffler. I did manage to snug up bolts so that was a contributor as well.

Spraying water has helped in the past, but this time I have not heard any reaction. I sprayed from a hand held spray bottle, I guess I could try the hose and get a bit more volume just in case I didn't spray enough.

Good thoughts and it does sound a lot like it did the time I forgot to reconnect the map sensor hose, but it's connected. And I can see the EGR shaft going in and out so not stuck. No hissing I can hear.

Never mind the wishful thinking diagnosis. After listening to both several times back to back, there's not that much difference. I reset the ECU again just in case no real change. Reconnected the line to the brake booster and there really isn't much difference. I'll still try again to check the bolts at the manifold but my gut tells me that's not going to do it (like the manifold in leaking, but not because a bolt is loose)

OK, I think this will work. Original After removing brake from vacuum

Well as you can see, my attemp to upload failed.

Well OK, wishful thinking colored my diagnosis. It is true that it is cycling a less, but the "smoothness" is about the same. I dug into my phone and found a .mov version of my original video, and also for one I just took. When I play them back on my PC I do at least get to hear the sound, but I don't see any actual image movement. I'll post both here in hope that these versions will be playable to the group and more knowledgeable ears might be able to comment as to if I really gained anything here or not. ... I can only update the one from today because the original is 40m and there is a 30m limit. I don't have any way to shorten the original, so I'll just go with the current video and see if anyone has anything new to say about the sound I have now. This is with the brake booster out of the vacuum system. NoBrakeBooster.MOV

OK, I didn't hit a home run here, but it is idling a lot better with the brake booster out of the vacuum system. It isn't doing the RPM up/down thing anymore but it is still a bit rough. I am leaving it run out there a bit just in case the ECU is retraining. Then the next step will be to disconnect the battery again and attempt an ECU reset. But there is at least hope that the issue isn't terminal.

Congrats! And yes!!

Great, I guess you can teach an old dog a new trick or two afterall. I'll give it a try

Awesome. Congrats!

To eliminate the brake booster as the source of the problem, I think I will disconnect the hose to the booster and plug it and see if the engine runs better. Anyone see an issue with doing this?

Beats me, but someone else might know if that is a possibility.

Yeah I've learned that can be an issue. I got a wrench on all the ones you can get to from the top and a couple were a little loose. I got to 2 bottom ones that I could snug a little and 2 were tight. But there are still 2-3 that I can't get to with any tool that I have. I'll need to find a 9/16 box end that is at least 2 feet long and I might get to the others.

Well the IAC was a good thought, but it is still clean from the cleaning last Feb, as it the TB. So that's no it I also noticed as I limped it into the garage, brakes are not working well. I know @89 MJ already mentioned looking at the hose to the brake booster, but it looks completely fine. But what ever failed is something that is causing very bad idle and at the same time power brakes don't seem to be working either. I currently have the battery disconnected in an attempt to reset the ECU. It's a hail Mary but it's something to try. If that doesn't work I'll probably have to trust it to one of the local shops since I'm thinking this is quickly getting beyond what my ASTM degree can handle.