idle problems....only sometimes

[offroader461]

hey everyone...i have got a problem with my jeep

 

I have had my 87 MJ for 3 years now and a problem has just recently in the past year or so has started. Sometimes after i start it the idle with go up to about 2000 rpm and won't come down and sometimes it will drop to normal and then pop back up. i have a new engine and have pulled the throttle body and cleaned it, replaced iac, tps, etc and can't get it to stop...although it sometimes will go days without doing it but then just gets a bug up its a$$ and does it every start up...now the strange thing is if i start the truck and its doing this i shut it off and push the throttle linkage at the TB under the hood then start it back up it idles normally?? I am completly lost and would appreciate any help....MJ RULE

[feerocknok]

Could be a real light snag in your throttle cable somewhere. This'd make it so you can get the rpms down at the throttle body, but not at the pedal.

[Oizarod115]

one time my vacuum line that runs across the top of the valve cover (forget what it connects to) was undone, and my idle was high, like 1500-2000. vacuum leak/coincidence?

hope its some help.

-nick

[whowey]

Its your TPS. Classic symptoms of the TPS failing. Mine does the same thing. 88 4.0l. As it slowly worsens, messing with the throttle linkage won't work. Eventuallyt, it will just do it randomly. Also, it will eventually the idle will slowly work its way up on every stop.

 

Remember a manual tranny TPS, and the Auto tranny one are different.

[sinnaevd]

if it was anything like my firefly (and i sure as hell hope it won't be seeing as how the firely is a 3cyl POS) it is expensive as hell to buy brand new

[ROADLESS]

If your sure there are no vacuum leaks then you might try readjusting your TPS. This is how i fixed a similar problem on my MJ :idea:

[87manche]

Unplug and replug the TPS and IAC connectors. If I do that every few months my high idle problems go away. I keep meaning to put some dielectric grease in there.

Anyway, I second TPS, or a sticking IAC.

An AT TPS will work for an MT rig, you just have an unused connection on the sensor.

[whowey]

.

An AT TPS will work for an MT rig, you just have an unused connection on the sensor.

 

An AT TPS uses a square 4 prong connector, the MT one uses a flat three prong(think trailer plug)

[87manche]

odd, the one I saw looked just like my MT one. Perhaps it was an Ho one. it ended up that the parts guy had no freakin clue, so who knows what he was showing me.

Thanks for the clarification.

[ROADLESS]

edit... high idle problems go away. I keep meaning to put some dielectric grease in there.

Anyway, I second TPS, or a sticking IAC.

An AT TPS will work for an MT rig, you just have an unused connection on the sensor.

No disrespect but instead of dielectric grease, i highly recommend using OX-GARD on electrical fittings, particularly where contact is made :brows:

It improves conductivity whereas dielectric actually insulates connections and can hinder conductivity. I found this out by trial and error(s) by applying dielectric compound to my TPS connection and finding out that it did not help. As soon as i cleaned the dielectric out of the connection and applied Ox-Gard, my TPS performed normally!