MayDay!! - Hard Accel Killed Idle

[89 MJ]

52 minutes ago, AnotherOldJeepGuy said:

What is the downside to removing the EGR?  Doesn't this mess with the ECU?

People that have to experience emissions testing will not pass without EGR. If you do not have to go through any sort of emissions testing/inspection, there is no downside to deleting it that I have heard. All it does is feed your engine's waste right back through it, reducing efficiency. 

[AnotherOldJeepGuy]

OK got it.

 

Does anyone know of an EGR Delete Kit?  

[Eagle_SX4]

31 minutes ago, AnotherOldJeepGuy said:

Does anyone know of an EGR Delete Kit?  

@boxyjeep sells ones.

https://boxyjeep.com/products/jeep-cherokee-4-0l-egr-plate-1987-1990

 

[AnotherOldJeepGuy]

Great!  If I decided to go this route I'll definitely give boxyjeep the order.

[Gojira94]

1 hour ago, 89 MJ said:

All it does is feed your engine's waste right back through it, reducing efficiency

 

Totally agree with getting rid of the EGR if your state won't ding you for it. Surprisingly, the siphoned exhaust gasses help reduce combustion temps. Two benefits - reduce chances of pre-ignition/ detonation from elevated combustion temps and reduce oxides of Nitrogen (NOx). High NOx is what fails emissions when EGR is deleted or not working properly. Most people don't like the idea of the buildup of combustion by-product in parts of the 'clean' intake side of the engine.

[AnotherOldJeepGuy]

Here in TX emission testing is no longer required for vehicles over 25.  (IIRC I think there are a few TX cities that do require it but not where I live). [Oddly enough the state still collects the same annual fee, just discontinued the test, way to go politicians]

 

I'm not sure I fully understand that last part, "Most people don't like the idea of the buildup of combustion by-product in parts of the 'clean' intake side of the engine", is that a Pro or Con to EGR Delete, sounds like it's a Con?

[Gojira94]

2 hours ago, AnotherOldJeepGuy said:

that last part, "Most people don't like the idea of the buildup of combustion by-product

 

A bit of exhaust is siphoned into the intake manifold upstream of the injectors. There tends to be a gummy/ sooty buildup of stuff that would normally be going out the tailpipe in the EGR valve and in the intake where it's attached. We normally would picture nothing but clean filtered air and fuel going in the intake...

 

Reduction of combustion temps via EGR matters the most for newer generation engines with relatively high compression that depend on EGR for:

1. using all the timing it's calibrated for to produce/ maintain rated power/ torque levels (reduced temps/knock retard)
2. to minimize NOx to meet emissions standards

For an old engine design essentially from the end of the 50s, with 8.8:1 static compression, that runs on low octane fuels, EGR isn't doing a lot for it.

[AnotherOldJeepGuy]

Thanks for all the input so far.  

 

Before I tear in to lots of disassembly, I feel like I need some education.  The INTAKE manifold has multiple vacuum hose connections.  It makes complete sense that the intake side, which is sucking in air, is a great source for creating a vacuum.

 

I also understand that the INTAKE and EXHAUST manifolds share a common set of mounting bolts, and they share a common gasket, so if the bolts work loose it effects both, and therefore effects the vacuum source.  I also note that in this gasket although a common gasket, each orifice is independent, i.e. the intake and exhaust pathways do not share the same air space.

 

Opposite to the Intake Manifold, I see a total of 0 vacuum ports on the Exhaust Manifold.  So since the exhaust path is independent of the intake path (let's for the moment assume the bolts are all tight and the gasket is intact) exactly how would a crack in the exhaust manifold have any effect on the vacuum??

 

 

[Eagle_SX4]

55 minutes ago, AnotherOldJeepGuy said:

exactly how would a crack in the exhaust manifold have any effect on the vacuum??

It does not affect vacuum at all. The problem is that the oxygen sensor reads lean because of the extra air being sucked in to the exhaust and causes the computer to add more fuel. Making the engine run richer than needed, it has a hard time burning the extra fuel, causing the stumbling and poor running. 

[AnotherOldJeepGuy]

Ah OK.  I understand better now, thanks for clearing that up!

 

So it sounds like maybe I have two problems.  A lack of vacuum is for sure (HVAC vent control not there at least at lower RPM, and possibly the reason the brake booster is not boosting) plus also engine stumbling.  Maybe that's a clue.  Maybe what I have is a blown or broken gasket since that would effect both the intake (lack of vacuum) and the exhaust (O2 sensor issue).  The other common point is the block, I don't want to go there....

[AnotherOldJeepGuy]

On 4/13/2026 at 4:18 PM, Eagle_SX4 said:

The more I think about it, the more I am leaning towards cracked exhaust manifold.

 

Pull the air box out and you should be able to see the exhaust manifold and watch it while it is running. Or if you have access to a smoke machine stick it up the tailpipe and check for leaks. A bee smoker can work as well if you have one.

I took out the airbox and that helped gain access to one of the manifold bolts I could not reach before and it did tighten a bit.  That leaves only one bottom bolt I can't get to from top or bottom with any leverage.  From the top the only way I think I can get to it is to remove the brakes and I'm not ready to do that.    I got a wrench on it from below good enough that if it is loose, it's not loose enough to tell with minimal leverage.  I'm willing to bet that one bolt that is at least very snug is not it.

 

With the airbox out I put the flashlight eveywhere I could and I cannot see anything that looks like a crack, and I didn't see any smoke.  I don't have anything I can use to blow smoke from the other end.

 

I am also watching @Porquer "Funky Idle" thread since his symptoms at least are very much like mine.

Edited 15 hours ago by AnotherOldJeepGuy
typo

[JZLAJeep]

1 hour ago, AnotherOldJeepGuy said:

That leaves only one bottom bolt I can't get to from top or bottom with any leverage.

Crows feet and extensions make those bottom bolt's doable. There are torque specs and a tightening order on the manifold bolts.

[derf]

10 minutes ago, JZLAJeep said:

Crows feet and extensions make those bottom bolt's doable. There are torque specs and a tightening order on the manifold bolts.

Wobble sockets on an extension work well too.

 

Something like this...

 

https://www.amazon.com/GearWrench-84917N-Universal-Impact-Socket/dp/B00UM687VG/ref=mp_s_a_1_4?crid=3NBXWZYA0WP6K&dib=eyJ2IjoiMSJ9.6K4ar_rF-VL699eznTCOKRJo2KDsoGB-pRvzaNZFxMaTSRTD2LfVisraArVYSc2TQKk0QR6E2WdtLZyFsh7BS3I9dzu0nnGQvbrj8dvcI_wSWr5V2r_A9WHXnqsQSNSBaWVMT3al5lpWHm9JgVSNiTkbenlVMZ35NDsoSipG6C3tX-_Mqi0Q8DQIHdPp5-kSKrHMGzdxrAlh6vIjuKcgpw.Q_sWnKVtpJrmH5EPLyZO1Hzi4MpY1-CYbo8Eo7t5OFY&dib_tag=se&keywords=wobble+socket+set+sae&qid=1776697907&sprefix=wobble+socket+set+%2Caps%2C356&sr=8-4

[AnotherOldJeepGuy]

Never heard of a wobble socket, looks like it could be useful.  Also never heard of crows feet but after looking it up I have seen these, just didn't know the name.

[derf]

4 minutes ago, AnotherOldJeepGuy said:

Never heard of a wobble socket, looks like it could be useful.  Also never heard of crows feet but after looking it up I have seen these, just didn't know the name.

I use the wobble sockets on my CJ with the 258.  I haven't pulled/installed manifolds on a 4.0 yet but I will soon.  I suspect the wobble sockets I have will get some use.

[AnotherOldJeepGuy]

4 hours ago, derf said:

I use the wobble sockets on my CJ with the 258.  I haven't pulled/installed manifolds on a 4.0 yet but I will soon.  I suspect the wobble sockets I have will get some use.

I'd be very curious to hear how you got to each bolt!  From top or bottom, what tool, and so it, if you are so inclined to post that level of detail .  In the mean time I am going to check ebay for a single 9/16 wobbler to see how it goes.

[derf]

2 minutes ago, AnotherOldJeepGuy said:

I'd be very curious to hear how you got to each bolt!  From top or bottom, what tool, and so it, if you are so inclined to post that level of detail .  In the mean time I am going to check ebay for a single 9/16 wobbler to see how it goes.

I came in from the bottom for several of them.  Even some of the exposed top ones don't have a straight path so the wobble lets you get the extension out past the manifold to get a useful sweep on the ratchet.

[AnotherOldJeepGuy]

8 minutes ago, derf said:

I came in from the bottom for several of them.  Even some of the exposed top ones don't have a straight path so the wobble lets you get the extension out past the manifold to get a useful sweep on the ratchet.

No surprise there!  Was mainly asking about the 4.0 once you get there and particularly for the lower back 2, these seem to be the worse cause both the exhaust pipe and the brake booster are in the way from the top, and unless you have really long skinny arms the are very hard to reach, for me at least 

[derf]

2 minutes ago, AnotherOldJeepGuy said:

No surprise there!  Was mainly asking about the 4.0 once you get there and particularly for the lower back 2, these seem to be the worse cause both the exhaust pipe and the brake booster are in the way from the top, and unless you have really long skinny arms the are very hard to reach, for me at least 

My CJ definitely has more room to maneuver.

 

I plan on attaching the manifolds to the engine before I drop it into my MJ.  Which is cheating a little.

[AnotherOldJeepGuy]

UH, yeah, just a little 

[JZLAJeep]

12 minutes ago, AnotherOldJeepGuy said:

Was mainly asking about the 4.0 once you get there and particularly for the lower back 2, these seem to be the worse cause both the exhaust pipe and the brake booster are in the way from the top...

Removed and installed manifolds a couple times from 4.0s (Once in '94 Xj, once in MJ) in the engine bay. It is tricky and takes some acrobatics, but can be done with hand tools (including a torque wrench) with crows feet, wobblers, and a variety of extensions and plan to work by feel and not sight.

[Eagle_SX4]

The 4.2 manifold is a lot easier to remove because the runners are about 1/2 the length of the 4.0 runners. I have changed every type of 4.0 manifold in my truck(Renix, H.O. and horse shoe) I was able to get to every bolt from the top with the airbox removed. Yes it does take some acrobatics to get to the rear most ones but it is possible. I didn't have any wobble sockets but did have wobble extensions. Like these.

https://www.homedepot.com/p/Husky-3-8-in-Drive-Wobble-Extension-Set-3-Pieces-H3DWOBEXT3PC/202923528

 

 

[AnotherOldJeepGuy]

I don't see the wobble aspect of these just in the pic but my local HD says they are in stock so the next trip out I'll go take a look.  Probably something handy to have around for more than just this job.

[derf]

1 minute ago, AnotherOldJeepGuy said:

I don't see the wobble aspect of these just in the pic but my local HD says they are in stock so the next trip out I'll go take a look.  Probably something handy to have around for more than just this job.

If you look close at the end of the extension, you can see that it's not straight like a normal extension.  It allows the socket to wobble when you put it on.

 

The only real drawback is that they're a little weaker than a standard extension.  The 3/8" drive is fine for manifold bolts.  The 1/4" extensions arent too hard to shear off with a good size ratchet.  Ask me how I know.

 

I had forgotten about those extensions.  They should work too.

[AnotherOldJeepGuy]

Yeah the 2 underneath ones I was able to get to from the top I did use 3/8 extensions without breaking anything, although it has been a while since I could simulate a 900 lb gorilla torque.