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91 Cherokee wont hold idle

J

jeepmadness

NAXJA Forum User
Location
mt vernon
4.0 Lardeo hasnt been started for 3 months. Want to get it back on the road to give my son. Things I have done before hand.

- new starter --- starter was burnt
- charged batter.
- new plugs, wires, cap, rotor.
- new air filter.
- Had to replace clutch mc and lines.
- Cleaned throttle body.

Jeep starts can rev engine but once I take foot off gas it dies. No problems starting before i took it off road

Any other suggestions please.

Thanks Madness
 
I would start by cleaning the throttle body and checking all of the electrcial connections around that area. You should also check your battery connections and make sure they are all good.
 
Heard that if the battery is not cranking enough the fuel pump will cut off? Thats why I got it full charge.

I had already cleaned out throttle body. Will check electrical connections again.

Thanks.
 
Check the IAC and TPS, the two sensors on the throttle body. The Idle Air Controller (IAC) has a pintle that moves in or out to allow air into the engine (bypassing the throttle plate) so it can idle...the pintle moves to control the air flow and thereby idle speed.

The Throttle Position Sensor (TPS) does have an effect on the position of the IAC, when you open the throttle it opens the IAC as well. However, I'm not sure if the TPS would cause the IAC to stay closed, but it's possible, a bad TPS can do some wierd things.

Either way, what you're describing is a classic symptom of the IAC not operating properly. You just have to figure out if it's the IAC itself or if there's another underlying cause.
 
I think your right its the IAC, trying to get the sucker off. Have a T20 socket but the sucker aint budging. Hit it with PB been at it for over an hour. That is just the first screw. Don't want to use to much pressure concerned about stripping the torx

Its never easy.
 
What year XJ? -edit- 1991 in main tiltle

It could be as simple as the fact that newer XJ's will loose the computer settings if you disconnect the battery for an extended amount of time or if it looses charge on you. When you go to start it the XJ it will idle roughly and stall if you take your foot of the gas. Start it up and drive around for 15 minutes. The computer will have reset itself by then and idle as normal.
 
Yes, yes...Tim is right. You may think that your battery is okay. But if it has a bad cell, the computer will forget the idle settings every time you turn the engine off.

Try a different battery. It worked for me.
 
Believe the ecm on the 1991 are not as sophisticated as the ODBII. I tested the map sensor after I pulled a code of 14.

See post pulled code 14. I think I tested it right. input no problem 5 volts.

output if i did it correctly no volts.
 
i just had this happen to me in my 96 sport it happened the first time and i got it home then it idle good again for about another week or two then the one day it wouldnt start at turkey hill for me so i rolled it to another spot tryed it for the heck of it and it worked...i then got out of schoo about 3 hours later and it wouldnt start at all. i got my dad and his friend to come jump me and it wouldnt idle at all i got it to the garage and they found out it was a loose negative battery cable...id say to check your battery cables and if its not that maybe the battery or alternator were the mechanics other two guess's before he found out about the loose dirty cable. hope this helps.
 
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