high idle on a 2.5 yj

greg slade

greg slade

The Moderated
Joined
Mar 21, 2005
Location
timberlake
man this litlle four popper has pushed me to my limits today. i recently picked up a 95 yj with a 4 cyl 2.5l. 165k on the clock. it had recently got a new motor, trans, t-case, all from the dealer all "expertly" put in by the previous owner. after re-installing everything properly and rebuilding BOTH diffs the dang thing wont idle below 1150. its got a aftermarket header and a tb spacer and cold air intake too.
i replaced the iac motor and tried three different tps sensors also i resealed the intake manifold and the tb with new gaskets. still no luck!!
one of my colleagues at my shop recalled that the only GOOD tps for those jeeps came from the dealer. anyway i have verified that there are no vaccum leaks and replaced all vac hoses.
ignition timing and tps range are both non adjustable on this vehicle, sooo????

usually i wouldnt bother with the 4 cyl and go ahead and drop in a LT1 but im trying to build a featherweight this time and besides the motor has 250 miles on it. not rebuilt or remaned but new new new.
i was hoping that some of you who currently run this setup have already came across a problem similar with the aftermarket parts.
my next only choice is to replace the intake manifold, maybe its warped and leaking a little????
TIA, GREG
 
You tried everything I would have tried. When I installed my spacer I crossed the tranny TV (auto) and throttle cables but I got much higher idle (3000). The only thing left I think you should check is that the throttle cable is returning completely and not binding because of the increased angle as a result of the spacer. The spacers provided for the cable bracket won't work on the 4 cylinder. Other than that I can't help you.
 
NO DICE. It idles too high even w/o the throttle cable attached, i even adjusted down the throttle stop screw under the tb. oh yeah, its a 5 speed.
 
high idle

check your intake for cracks near the throttle body, before it goes into seperate runners. if you have a crack there it will idle high, if it has a crack at one of the runners it will miss like a bastard. also is it a mass air system or map sensor system? Either one of those sensors will have an effect on idle. An easy way to check for vaccum leaks is to spray carburaetor cleaner or brake parts cleaner on the intake while it is warmed up, this will force the engine rich if there is a leak and cause it to miss or rev up. lemme know what you find, I work on yotas for a living and we get alot of vaccum leaks.
 
i tried all the old tricks to find a leak but to no avail, thats why im thinking a small crack in the intake. i inspected it closely (i thought) when i reinstalled it and found no cracks.

the motor is a speed density system so it employs a map sensor instead of a mass air flow meter. it was my understanding that the map could not cause this symptom as it only sees sudden decreases in manifold vac and richens the mixture accordingly?

it runs well thru the whole rpm range with abolutely no missing or driveability problems. a quick call to the, ahem "mechanic" who put the engine in and i found out that the problem appeared after putting in the new motor. thats why i was curious about the tendency of these manifolds to warp as well as crack. if it was warped to the old head, when installed on the new one, woollah a small leak. but again i cant figure out why i cant idenitfy where the leak is coming from. i used carb cleaner, ETHER, and then a propane enrichment tool. still ZERO SIGNS OF A LEAK.
i am very familiar of their tendency to warp and crack ex. manifolds as i replace these weekly at my muffler shops.

does anybody have a spare intake to sell in case mine is cracked or just to borrow and try?

project cheap jeep is becoming a headache and time is money!!!!!!
 
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