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so, over the past several months i've tried to diagnose & fix my weird idle issue. first thing out of everyone's mouth is "vac leak" but read the symptoms.
in the morning when i first start the Jeep (7am) it's got a low idle, somewhere around 500rpm. once warmed up it runs perfectly. no idle issues, good power, runs like it should.
in the afternoon when is start it up, it start normally and idles but has a very rough idle, almost like it's missing on a cylinder or two. once it warms up it runs fine on my drive down the street from work. in almost the same spot on my drive home it starts idling high (1500-2500rpm) and will continue to do so until i shut it down & restart it. once restarted the idle sits steady at 750rpm for the next 15minutes or so then it goes right back up to high idle again.
what the fawk is wrong with this thing??
i'm thinking maybe i need to change out the injectors?
i have a new CPS but haven't installed that yet?
so far i've replaced: IAT, WTS, IAC, MAP, O2 sensor, FPR, EGR solenoid, adjusted the TPS (which tests good), adjusted the NSS, replaced the fuel filter, has a good tune-up, new air filter, wire harness is grounded correctly, all vac lines look good and i hear no leaks.
it's goddam frustrating.
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Did you test the coil? Was that part of the tuneup?
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hmmm, nope. haven't tested the coil....
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at this point, if the TB and intake is clean. O2 sensor is good, then I'd maybe swap computers and see what that does. I'm sure there is one laying around somewhere. I know I have one for a renix.
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How about checking all the sensor wires for wear and shorts? ...bad
ground someplace (that makes all kinds of wierd stuff happen)? The
main computer or the wires out of it to the various operating
controls?
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I was thinking the 'puter too, maybe a loose connection.
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yeah, that's really the hard part is checking all the connectors & wiring for shorts.
i think i'll test the coil, swap it for the spare i have that i know is good and then junkyard me up a new engine harness & try that. then a computer swap.
boo this. i love my jeep, hate the way it runs right now.
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Yank out the computer and all of them sensors and wires. Go propane.
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If you can send your injectors out for cleaning. Also, what did the
IAC passage look like? I just had similar problems on my honda, and
there was a little screen in the IAC passage on the valve that was just
carboned up. Cleaned it and the problem is gone. A vacuum leak will
give you high idle. I'd look at the idle circuit, and make sure
everything is clean. Also, how do the throttle shafts wear on these? I
remember that could be a load of frustration on carburetors.
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IAC passage & the rest of the TB is clean. plate looked fine, no play that i could tell.
would a vac leak cause it run at 500rpm at start-up & then perfectly fine only in the mornings?
do vac leaks go away when you shut off & restart the engine?
this problem is electrical.
this only happens in the afternoon which lead me to replace the IAT & MAP, but no joy. the only idle circuit on a TB is the IAC bore, which is clean and NOT variable. as for the injectors, they'll just need to be replaced. no time to have them cleaned, plus they're 20yrs old.
i'm thinking maybe a sticky & leaky injector(s) is the problem.
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Spray along the gasket with some carb cleaner or something and listen
for a change in idle speed.
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it's goddam frustrating.
I hear that! I STILL haven't figured mine out yet. But I haven't replaced the manifold gasket yet.
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I've got all my old parts. Including a coil. Come on down & swap um 1 by 1 8)
But it's a 96
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Spray along the gasket with some carb cleaner or something and listen
for a change in idle speed.
I did that. But with WD40 and water
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Not so sure on the leaky injector thing. More gas is not gonna make it
idle faster if it's not getting more air too is it? I had a fast idle
problem when my tps went bad, but you said you checked that. Did you
check the tps while the problem was happening?
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i've tried all that. no leaks that i can find by spray or by ear/tube/stetho.
like i said before, the vac leak answer is a little played on this one.
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Not so sure on the leaky injector thing. More gas is not gonna make it
idle faster if it's not getting more air too is it? I had a fast idle
problem when my tps went bad, but you said you checked that. Did you
check the tps while the problem was happening?
well, yes & no. i'm thinking a stuck shut injector may lean the mixture to the point that the computer up's the fuel table and bumps the IAC.
the stuck injector may then leak down the pressure in the fuel rail overnight causing my rough/low idle at morning startup.
all this is theory so far. damn, why do i get the tough ones?
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It's obviously the CPS then. :)
I'd say it's due for new injectors. Get the 24lb ford motorsports ones
with 4.6l injector mounts.
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i thought we were supposed to run the 19lb stock 5.0 injectors? i AM going to order some, wanna get the right ones. this is an '88 Renix. thanks for the help.
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I'm not sure what you're supposed to run in the stocker. The 24lb
injectors require a special 4.6l fixture.
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I've got the stock 200k mile ones from my Renix I can mail you if
you'd like. I replaced them with 19lb 5.0 ones and didn't notice a
bit of difference, aside from slightly better throttle response.
Some things just can't be duplicated without alcohol!
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Warning: Contains smartass comments with no real help... sorry JB, but I don't have any other good ideas other than what has already been suggested.
ISSUE:when i first start the Jeep (7am) it's got a low idle,
ANSWER: your Jeep is not a morning person. Let her sleep in a little later =).
ISSUE: in almost the same spot on my drive home it starts idling high (1500-2500rpm)
ANSWER: There's something at that spot that peaks her interest & gets her motor revving... ISSUE: I shut it down & restart it. once restarted the idle sits steady at 750rpm for the next 15minutes or so then it goes right back up to high idle again. ANSWER:on the bright side, if you turn her off, she still gets interested again pretty quickly =).
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"what the fawk is wrong with this thing??"
I think lobster hit the nail on the head! It's a woman. Start calling him Gus, or Bruno...
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LOLzzzz
thanks for the help.
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okay, i swapped out the coil which did smooth out the idle a little bit. however it didn't do a thing for the low/high sporatic idle issue.
i'll be swapping out the CPS tomorrow.
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