Rough idle (no codes) smooths out with acceleration

Jscam

Jscam

New Member
Joined
Aug 26, 2019
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8
Location
New Orleans, LA
Hello all, I’m sure this has been asked before but can’t find my specific symptoms. I have the 4.0 (non distributor) and over night it began running super rough at idle. About 5 months ago I replaced all kinds of things under hood when I bought it (belt, water pump, thermostat, pulleys, radiator, fluids all around, rear main seal, oil pan gasket, valve cover gasket, spark plugs, check valves, new vacuum hoses, pcv valves, cleaned the throttle body spotless, iac and tps sensors. I,m sure I’m missing something there in that list. The Jeep ran good until now.

I’m not having any trouble starting the Jeep, it starts right up every time. While idling it shakes like crazy, but apply the slightest amount of throttle and it smooths out like it was rolling off the lot new in 2004. The rpm never flutters it starts rock solid around 500 rpm. Driving it has no loss of power at all, but again, let off the gas and we are back to the big block cam feeling. I have seaformed it in the past just to make me feel better but didn’t really need it. Additionally the Jeep is not blowing smoke at all either nor is it throwing any kind of codes. Just for fun I pulled it up anyways to see if had any stored.... nope. I’m running out of ideas here :( could the fuel pump be going out ? thanks for the help!
 
Sure sounds like a dirty IAC to me, but you say you replaced it, right?

I hope your your sake you've been replacing things with OE Mopar parts.
 
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My guess is a defective or dirty IAC. Less likely a bad TPS. Single-tipped platinum spark plugs like the Autolite AP985 or Champion 3034, even though some guidebooks say they are OK, can cause a bad idle/misfires too. But that you say the problem goes away when you step on the gas a little leads me back to the IAC. Or a dirty orifice in the TB where the IAC's plunger goes.
 
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Chris said:
Sure sounds like a dirty IAC to me, but you say you replaced it, right?

I hope your your sake you've been replacing things with OE Mopar parts.
Click to expand...
Jerry Bransford said:
My guess is a defective or dirty IAC. Less likely a bad TPS. Single-tipped platinum spark plugs like the Autolite AP985 or Champion 3034, even though some guidebooks say they are OK, can cause a bad idle/misfires too. But that you say the problem goes away when you step on the gas a little leads me back to the IAC. Or a dirty orifice in the TB where the IAC's plunger goes.
Click to expand...

I have the same exact problem, but @Jscam explained it better than I did.

I'm going to try these, starting with IAC.
Grateful.
 
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Any limitation on brand for replacement IAC? I know people have reported that the TJ can be picky about sensors, didn't know if this included the IAC as well.
 
Chris said:
Let us know how it does (y)
Click to expand...
Chris said:
Let us know how it does (y)
Click to expand...

I just changed it, I STRUGGLED a lot with removing one of the screws damn it (the one below).

After I connected everything I started the engine,
and the RPM was like 3000 xD I said:
"let's wait a moment maybe it'll be reprogrammed or something hehehe.. but it didn't!"

I turned the engine off, then I stared again.. IT WAS DONE.
RPM below 1000 when idle, the engine is very quiet right now
it doesn't run rough

I took it for a test drive (Two photos below, one of the new IAC part before installing it, and the second photo while the car on D but holding Brakes.)


THANK YOU BOSS.

IMG_5983.jpg


IMG_5986.jpg
 
q8ieng said:
I just changed it, I STRUGGLED a lot with removing one of the screws damn it (the one below).

After I connected everything I started the engine,
and the RPM was like 3000 xD I said:
"let's wait a moment maybe it'll be reprogrammed or something hehehe.. but it didn't!"

I turned the engine off, then I stared again.. IT WAS DONE.
RPM below 1000 when idle, the engine is very quiet right now
it doesn't run rough

I took it for a test drive (Two photos below, one of the new IAC part before installing it, and the second photo while the car on D but holding Brakes.)


THANK YOU BOSS.

View attachment 111961

View attachment 111962
Click to expand...

Thanks for the update. So it sounds like it worked out for you then?
 
Glad the new IAC fixed it. Did you also clean the orifice that the IAC's plunger fits into as suggested above? It is often nothing more than combustion byproducts/dirt on the IAC plunger and/or inside its orifice that is the main reason for IAC/idle problems.
 
Chris said:
Thanks for the update. So it sounds like it worked out for you then?
Click to expand...

Yes, it runs smoother now
Chris said:
Thanks for the update. So it sounds like it worked out for you then?
Click to expand...

Very happy, even the performance is way better than before.
I found the reason to that when I inspected the IAC as you suggested, it turned out that the IAC used before was not for my tj, it was of different design but the previous owner I believe he installed it anyway.
I noticed the difference between Mopar's and the one installed on my tj

Thank you.

Jerry Bransford said:
Glad the new IAC fixed it. Did you also clean the orifice that the IAC's plunger fits into as suggested above? It is often nothing more than combustion byproducts/dirt on the IAC plunger and/or inside its orifice that is the main reason for IAC/idle problems.
Click to expand...

I didn't to be honest, I forgot xD
but I guess it is clean, because when I took off the old IAC it wasn't dirty after all, but it was for different model.
 
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Never rule out bad gas . Just sayin. It stays on my list...maybe it’s my part of the country, but it happens .
 
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