Jeep 4.0 exhaust manifold glowing!

jbkelly0211

jbkelly0211

Well-Known Member
Joined
Jul 20, 2010
Location
Charlotte
This just started in the past few days, my 04 WJ will crank up fine, but idles at around 1,100rpm. Sometimes its will crank up and idle at around 700 but as soon as I put it in gear it jumps to around 1,100 again. I also noticed the other night that my exhaust manifold is glowing red and the exhaust is hot as :poop: . Any ideas? TPS, IAC, 02 sensors? i know it could be any of the above or a combination but I was just wondering if anyone else has had this problem that could give me a place to start before i just start replacing sensors that dont need to be. Also my CEL is NOT on, i figured if it was an O2 sensor it would be throwing some sort of emissions code.
 
exhaust and cat are clean as a whistle, doesnt glow red past manifold, has to be running lean. Any ideas where to start, one thing more common to fail than others. I'm failrly certian it is not a vaccum leak, traced all hoses and everything seems ok. What is correlation between high idle and running lean?
 
remove and clean your fuel injectors, make sure they are spraying adequately. if one or more of those suckers is clogged then you will have a multiple misfire due to the extreme lean condition. is it the stock manifold? also check your fuel pressure.
 
Ths thread is full of mis-information. Address the high idle issue first. That will most likely fix the glowing manifold issue. I see manifolds on 4.0's glow every time I break in a cam or hold the throttle open for a prolonged amount of time during diagnosis or repairs. The cast iron, later model, dual manifolds seem to do it more so than the older "header" style ones did.
All of that being said, I see and replace a lot of throttle position sensors here at my dealer on later 4.0's. They won't trip a CEL, but will show partial throttle even when closed and thus cause a high idle.
If you're in the mood to throw parts at it, I would start with a TP sensor. Or it may be worth it to have it diagnosed to be sure.
 
Thanks, I knew the heat had something to do with the high idle, just wasnt sure where to start, looking around now for a used TPS first, then ill check new prices. Its still runs smooth, no misfires or hesitations. The TPS isnt really a serviciable part is it, it cannot be opened up and cleaned with parts cleaner? If im going to replace it anyways, i might just tinker with it and see if something is visibly wrong.
 
Never really looked at the TPS on a 4.0 before, but on most other cars you can make adjustments by loosening the screws and moving the TPS. Other than that adjustment I know of nothing you can do to service it. Typically, you'd do this in conjunction with a volt meter to find the proper voltage. I never worry with it anymore and just replace it. Pretty cheap part.
 
Ok sounds good, i just called and was surprised, they are cheaper than i expected. I will get it on when it comes in and update if it solves both issues. Thanks for the help.
 
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