Rough idle on 98 TJ 2.4

[ash.4.keeps]

Hey Y'all
First off I'm a New Jeep Owner I just purchased my 98 TJ 2.4 manual about 2-3 weeks ago and really love it so far. However, after about a week of owning it I noticed that the idle started to have some issues.

-First it was just a small rough idle, around the 800 -1000 RPM range and would go back and forth about every 5 seconds.
I figured this could have just been dirty plugs or an air leak somewhere. Well, after a few days of looking couldn't find any.
- Few days later it started getting worse. Idle jumped up to the 12-1800 range. Now starting to worry, so I replaced the plugs and after numerous research videos on youtube i cleaned out the throttle body, idle control valve, the dreaded "T" valve, and new air filter.
-After cleaning the throttle body, the idle seemed a bit better but it was only for a day and its back up idling rough again. this time i think the AC is now involved as well.

Any help would be much appreciated.

Thank you all.

*PS... I got my first Duck Yesterday!!! The cutest thing ever! ... Thank you to who ever you are and cant wait to Duck It Forward!


Ashley

 

[Jerry Bransford]

Idle goes to 1800 only when the a/c or heater is on? That makes me think vacuum leak somewhere in the HVAC system since the problem only shows up when selecting a/c or heat. Like in the HVAC control head. Especially if the 1800 rpm idle only happens when the a/c or heater/defrost is selected.

 

[Chris]

Sure sounds like a vacuum leak to me as well, I would have to agree. A smoke machine is an effective way at finding difficult to see vacuum leaks.

 

[ash.4.keeps]

Just as another precaution I ordered the valve cover pvc elbow valves (47079/47057) and the grommets 42344. I am also going to do the cigar smoke trick to see if I can find any other leaks. However, I may be a little uncertain on where or what hose I start the smoke at.
Would it be the air intake into the manifold?

 

[Rubicon88]

You have a 2.5 engine in a 1998.

#1
The behavior on a cold start is?
(Cold start meaning not run in at least 3 hours)

#2
The behavior on a warm start?

#3
Comparing the two the differences are? You need to do this test and observe the behavior with the hvac system off. No defrost, no AC...etc.
Then repeat with the AC on

#4
Is your CEL on?

#5
Reset the system. Might not do anything but with everything you've changed it won't hurt.
Detach the negative battery cable at the battery. Turn key on like you're starting it (not just on but like you're trying to start it) hold there for 10 seconds.
Turn key off.
Attach negative cable.
Start and run. Evaluate.


Start with those few observations before throwing the parts store at it and report back.

Good luck

 

[ash.4.keeps]

You have a 2.5 engine in a 1998.

#1
The behavior on a cold start is?
(Cold start meaning not run in at least 3 hours)

#2
The behavior on a warm start?

#3
Comparing the two the differences are? You need to do this test and observe the behavior with the hvac system off. No defrost, no AC...etc.
Then repeat with the AC on

#4
Is your CEL on?

#5
Reset the system. Might not do anything but with everything you've changed it won't hurt.
Detach the negative battery cable at the battery. Turn key on like you're starting it (not just on but like you're trying to start it) hold there for 10 seconds.
Turn key off.
Attach negative cable.
Start and run. Evaluate.


Start with those few observations before throwing the parts store at it and report back.

Good luck

Will test this out and get back to you... Sorry 2.4 was typo.

 

[Rubicon88]

Will test this out and get back to you... Sorry 2.4 was typo.

I figured as much...
The more details you notice the more help can be offered.

 

[ash.4.keeps]

OK quick update. Did the smoke test and was able to pin point a small tear in one of the lines that was on the back side very small could only find with the smoke. Cut that piece out and seems to be idling fine at the 5-600rmp.

**I just want to thank you guys for the help and the advice. This was my first post and really appreciate the quick responses and awesome help!

Thank you!

Ashley