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Never seen the jeep do this before.. all i did was raise the idle by 100rpm and now when i shut it iff.. the engine shakes and clacks loudly like its detonating in the cylinders.

I did put 87 octane in the engine and ive been using 93 as i noticed on the interstate it predetonates at higher rpms so for like 3 or 4 years ive been using 93 not 87

Could it be the 87 ? Ill put 93 backcin but yea...

I would switch back to 93. In the meantime I would also add some octane booster and see if that helps.
Carbon buildup can cause hot spots in the chamber. I picked up a junk mower a few weeks ago that would do exactly that when you released the bail. It would actually keep "running" for about 3-5 seconds when it was hot. I pulled the head off and wire wheeled everything. Problem was solved.
I know its apples and oranges but carbon can cause all sorts of issues.
Raising the idle could cause just enough fuel to enter the combustion chamber to start auto ignition on a hot spot.

Yea i noticed this too.. when i turned the key off the engine wanted to keep running and sputtered for like 2 seconds... i was like wtf is this. Ill drop the idle bsck down.. i just dont like how my idle drops by like 50 to 100rpm when the a.c is on.. that drops brings it down to like 500-550rpm and its too low to keep the alternator charging properly with the headlights and a.c on at a stop in gear. I know its hard to believe but the alternator charges much better at idle 650rpm vs 550rpm.. just that 100 rpm boost csn raise the voltage way up with everything on

I wish there was a way to get the engine to pump idle up when the a.c is on. I know the carb has that electric nipple that pushes out on the throttle lever.. but i dont know if that turns on for the a.c or something else. But i dont like the idle dropping like that when the a.c is on. I wonder if i can bypass that little plunger thing.. by splicing the wire into the a.c clutch power wire. So when the a.c clutch is turned on itll push that nipple out and raise the idle up.

Am i making sense ?

I put 20$ of 93 in i was nearing empty.. drove it around and it shuts off better.. but idle at stop lights the engine has some vibration...

Maybe ill try some seafosm or water in the carb slowely see if thatll help if it is carbon

Engine is still shaking.. it diesnt do it in shutdown but when idling the vehicke has vibration in it when it didnt hsve that before.. and the tailpipe exhaust sounds like the engine is missfiring almost has slight poping in the exhaust noise.

Anyone ?

Yea i open the hood and the whole engine is vibrating now.. its never done this before.. csn anyone help me or is this forum dead now

Ok i found the issue... the vacuum nipple behind the intake is open my little plug i put on it came off... put my finger on it to stop the vacuum leak and the engine stops shaking... glad it was simple.. i was thinking i had valve sticking or something major lol

Thanks for reporting what the issue was. I appreciate it because I keep all these little things in mind when my Jeep starts acting up!

Yea it freaked me out, i was like man...... the whole engine was vibrating. i recorded a video of it, and it was shaking... and when i had the air cleaner off to adjust idle again i noticed the L shaped nipple behind the carb was missing its plug on the top "removed the stock air hat and a ton of the useless vacuum lines and plugged this one" Once i put my thumb on it the vibration stopped and it idled better. Not sure how the plug came off but i might have poped it off somehow when i removed the air cleaner to adjust the idle the first time.. put a tighter fitting plug on so it shouldnt pop off this time

Weird how a vacuum leak like that can cause so much vibration and how it caused poping out of the tail pipe.. I really thought i bent a valve or something serious

Here is the video.. see the vibration ? My engine normally is super smooth and i have 0 vibration

https://www.youtube.com/watch?v=VxREuFD ... e=youtu.be

Those low compression engines should not need high octane gas anyway.

If you remove all the vacuum lines and emission stuff the engine needs calibrated or timing adjusted. I heard if you remove the egr itll ping with 87.. I dunno how to adjust all that stuff yet so i just put 93 in.

Running one cooler heat range of plugs can help run on if you still have problems. I run autolite 84

Ive done that on my 5.9 zj as they have pinging issues they are high compression engines thougj.. but it can also cause carbon build up running colder plugs and lower gas mileage. I noticed a drop in gas mileage doing that on my zj

candymancan wrote:Ive done that on my 5.9 zj as they have pinging issues they are high compression engines thougj.. but it can also cause carbon build up running colder plugs and lower gas mileage. I noticed a drop in gas mileage doing that on my zj

In our case the heat range of the champion that's specified comes in between the autolite 64 and 65 so staying with one of those 2 should be fine. One nice thing the 64s are gapped at 37 so they're about right for EFI/ tfi coil people