[Gsmyth75]

My jeep tends to idle up to about 1,100rpm then back down to about 500rpm and start sputtering every once in a while then it will act normal for a while. It's especially annoying at lights when I start idleing into the person in front of me until i notice and luckely I haven't ran into anyone.
It also has a problem at wot around 3000-4000rpm where it tends to hang at that rpm speed for a second before increasing and it sputters while doing that too. So far I've replaced
Tps
Cap and Rotor
Spark Plugs and wires
Fuel Filter
Cleaned the Iac sensor like crazy
Seafoamed it
and I've replaced the map and Iac sensors with junkyard ones just to see if it made a difference.

For a while it ran fine, and didn't have any issues, but now this problem is back and I'm at a loss for what it could be, I've tried searching, and talked to a couple mechanics.
So far my guess is it's got to be one of these:
Cps
Fuel Pump
Coil
or bad map/ iac and I just got unlucky and pulled a bad one.

Any Help will be greatly appreciated.

[yoda13]

My XJ that is also my father's, we took on our trip to Colorado and has the same issues after I dunked it in the river. We had to replace the MAP, TPS, and O2 sensor before it would run right....it acted just exactly like you say yours is...just my experiences...thought it might help you...

[Gsmyth75]

Thank you, and wow quick response time. I think I'll try replacing o2 and see what that does. It probably couldn't hurt...

[BrunoS]

please .... sounds like bad IAC

[firefighter1c57]

Originally Posted by BrunoS

please .... sounds like bad IAC

IAC wouldn't effect it at 3000 RPM. I'd say TPS. Yea, yea, I know, you've already replaced it. I replaced about 3 in 4 months. Sensors are funny things, sometimes they are even bad from the factory. Just my 2 pennies.

[Gsmyth75]

Originally Posted by firefighter1c57

IAC wouldn't effect it at 3000 RPM. I'd say TPS. Yea, yea, I know, you've already replaced it. I replaced about 3 in 4 months. Sensors are funny things, sometimes they are even bad from the factory. Just my 2 pennies.

I've heard it's common to get bad sensors that are "new". But when I take off the tps at idle it quits/ barely keeps running, so i would think it does something. Is there any way to test if it works ? I have a multimeter but im not sure what all the other modes for it do other than dc volts? What setting would i use to test sensors? Also I cleaned a lot of gunk out of the iac sensor connector and it doesn't run as crappy at idle but it still does the 3k thing.

[edolivett]

you can prob rule out cps... cause they typically go bad pretty fast, and it usually wont even allow the car to start... my bet is on tps or coil.

[mickc9129]

I think that '92 was the last year you can adjust your timing. Might see how thats doing.

[BrunoS]

Originally Posted by Gsmyth75

I've heard it's common to get bad sensors that are "new". But when I take off the tps at idle it quits/ barely keeps running, so i would think it does something. Is there any way to test if it works ? I have a multimeter but im not sure what all the other modes for it do other than dc volts? What setting would i use to test sensors? Also I cleaned a lot of gunk out of the iac sensor connector and it doesn't run as crappy at idle but it still does the 3k thing.

ok, here's the key:

when you disconnect the TPS, the idle dies. on my xj, if i disconnect the tps, two things happen: check engine light turns on and idle stays exact same.

in your case, dying after disconnecting the tps means the IAC is overextended. they do die after many years of service, regardless of how much you clean it...there is a motor inside that gets wear spots and jumps around. at higher rpm, a stuck IAC allows more air or less air to go in the throttle body which then plays hell with the fuel injector pulse width ("on time") and the oxy sensors go nuts trying to correct the whole mess with erratic airflow due to a jumpy IAC.

here's my test: SIMPLY get the motor warmed up, get a decent idle, and disconnect the IAC motor. drive around. should be a nice ride, plenty of power, and smooth idle. if it's the case....you have a worn out IAC.

as for the TPS....disconnect it, borrow a analag (needle) volt-ohmeter, connect it to ohms...and run the throttle around and watch for a smooth needle movement...if it's jumpy, then a worn spot in the TPS. new tps these days are decent qualiity.

1) don't spend any more money on parts before
2) trying my warmed up idle, then disconnect the IAC motor connector and go for a full test drive.

[Gsmyth75]

Originally Posted by BrunoS

ok, here's the key:

when you disconnect the TPS, the idle dies. on my xj, if i disconnect the tps, two things happen: check engine light turns on and idle stays exact same.

in your case, dying after disconnecting the tps means the IAC is overextended. they do die after many years of service, regardless of how much you clean it...there is a motor inside that gets wear spots and jumps around. at higher rpm, a stuck IAC allows more air or less air to go in the throttle body which then plays hell with the fuel injector pulse width ("on time") and the oxy sensors go nuts trying to correct the whole mess with erratic airflow due to a jumpy IAC.

here's my test: SIMPLY get the motor warmed up, get a decent idle, and disconnect the IAC motor. drive around. should be a nice ride, plenty of power, and smooth idle. if it's the case....you have a worn out IAC.

as for the TPS....disconnect it, borrow a analag (needle) volt-ohmeter, connect it to ohms...and run the throttle around and watch for a smooth needle movement...if it's jumpy, then a worn spot in the TPS. new tps these days are decent qualiity.

1) don't spend any more money on parts before
2) trying my warmed up idle, then disconnect the IAC motor connector and go for a full test drive.

I warmed it up and drove it without the iac and it drove the same as when it was connected. I'm going to go get a new iac, install it and see what happens next. Thanks for taking the time to write out a iac test.

[BrunoS]

by saying idle didn't change after you disconnected the IAC after all was warmed up....you mean it drove fine, revved up fine, and then idled fine...

or that you have still the beserk jumpy idle....couldn't figure your response.

---------------------------

if after my test it idles smooth, (disconnected IAC connector) and (smooth as a 4.0 does, anyways) at the same rpm, around 750 or so...then you IAC is worn out. Replug it in, and drive around...beserk idle and driving after the reconnect would really indicate again the IAC problem

before spending $80+ on new IAC, take two torx srews (T-15?) that hold it into the TB and remove the IAC, pull it straight out, and inspect it...you may be surprised at the carbon and goo on it. try cleaning it with a toothrbrush and reinstalling it and driving it around again. sometimes this works...sometimes it's time for a IAC replacement.