4.2L Bogs down in low RPMs + idles high sometimes - JeepForum.com
LinkBack Thread Tools
post #1 of 4 Old 05-11-2019, 09:16 AM Thread Starter
Registered User
1990 YJ Wrangler 
Join Date: May 2019
Posts: 6
4.2L Bogs down in low RPMs + idles high sometimes

I need some help. I have a 1990 YJ with the 4.2L and carter carburetor. I inherited this thing after it sat for about 2 years. I've gotten it to be driveable (I'm not much of a mechanic, rely heavily on google and youtube). It runs and will stay idling now. My plan for now is get it running halfway decent and drive it around town and to work on nice days without doors and top. In a couple years I'll upgrade the carburetor, clean up the vacuum lines mess and all that jazz. My dad had 10+ jeeps that I can remember growing up and this was the last one he owned so I plan to keep it and fix it up overtime.

Issue 1: It seems to bog down and miss in low RPMs about 800-1500. When I pull out it stutters and catches up (sometimes squeaking tires if I give it enough gas). Also while in other gears if I give it sharp gas it stutters/misses at first then catches up. Also happens a lot up hills. Again, in the low RPMs. If I'm parked and idling and barely give it gas in the 800-1200 range you can feel it missing/hesitating pretty bad. Also if I turn the key off sometimes it'll sputter and just sounds like it's dying in gear or something before completely turning off.

Issue 2: I replaced the carburetor because idling and other issues. But sometimes it seems to get stuck around 1200 RPMs idling. Sometimes if I give it sharp gas it'll jump up and slowly go back down to normal (about 750). If I just let it sit it does not go down. This happens before and after being warmed up. The plunger looking thing attached to carburetor moves freely in and out on both sides when shut off. I have noticed if I push somewhat on the one side the screw is touching forcing it in it kind of clicks and goes in to lower the idle, sometimes it will not forcibly let me do that though. Maybe the choke is forcing this (not sure)?

I've tried testing the rats nest of vacuum hoses by spraying carb cleaner while running to listen for a change in idle but didn't notice anything. I've read you can hookup a vacuum gauge but I've found no specific video or instructions on how to do this for this model. Like I said, I'm no mechanic and don't understand how a lot of this stuff works. Just been googling and watching youtube videos.

List of things I've replaced related to this:
Distributor and rotor
Ignition coil
EGR valve
Carburetor with a reman from autozone

I appreciate any help, advice, or anything at this point. Thanks for reading!

mathena2 is offline  
Sponsored Links
post #2 of 4 Old 05-18-2019, 06:14 AM Thread Starter
Registered User
1990 YJ Wrangler 
Join Date: May 2019
Posts: 6
Anyone have any ideas?
mathena2 is offline  
post #3 of 4 Old 05-22-2019, 09:27 AM
Registered User
Join Date: May 2018
Posts: 14
Bueller? Bueller?

I have an 89 with similar issues and also in similar repair status. We’ve replaced the plugs and wires, but not distributed cap yet. Just replaced the main rear and oil pan gaskets, and converted to an external slave on the tranny. Replaced a few vacuums lines that were broken but not all of them. Right now we’re leaking oil so I’m trying to run that down. We also lifted it 2.5 inches, and put 31” tires so I know that slows us down a bit.

All that said, we bog a little in lower rpms (maybe up to 1100ish rpms) and in 4th and 5th gear. We also have a bit of an issue when I hit big puddles that it sometimes stalls out and won’t restart. I’m blaming that in the distributor, but haven’t nailed it down yet.

So here we are. 2 non mechanics waiting for our white knight go knowledge. I’ll let you know if I find anything as I wander about blindly on YouTube. 🙂.
Clancrawley is offline  
post #4 of 4 Old 05-22-2019, 07:52 PM
Registered User
1994 YJ Wrangler 
Join Date: Jul 2007
Location: Beer City
Posts: 1,323

Start here. Read it thoroughly and do what it says. Understand everything it has to say. If you cannot. I will take it off your hands for pennies on the dollar because you are in over your head and it will cost you more to figure it out than to give up on it.

Just kidding. great site. should help you tremendously if you have any attention to research and detail.

If you cannot fix it with a hammer then it has to be an electrical problem.
Boojo35 is online now  

Quick Reply

Register Now

In order to be able to post messages on the JeepForum.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.

Email Address:


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page

Similar Threads
Thread Thread Starter Jeep Forums Replies Last Post
My goal is to get 25+ mpg from my 99 XJ with 30 x 9.5 R15 ATs Charley3 XJ Cherokee Technical Forum 3853 02-12-2019 09:15 AM
Low Rumble when at 1000 rpms sphagetibear21 Engines & Drivetrain 1 08-17-2018 05:58 PM
CA Smog - Invisible MIL and High Low RPM NOx? Line58 TJ Wrangler Technical Forum 9 05-22-2018 05:08 PM
90 4.2l Engine starts up and drives fine but RPMs drop and stall when slowing down Bobthebobofbob YJ Wrangler Technical Forum 1 05-08-2018 02:31 AM
2008 3.7 jeep commander idles high high and high and is missing please help mlowe42 WK Grand Cherokee & XK Commander Forum 3 03-28-2018 05:08 AM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome