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View Full Version : 89 xj -high idle woes,dammit!!


bcmaxx
April 8th, 2008, 19:01
1989 xj 4.0, auto, Having problems with high idle, first appeared on the trail sunday, driving and stopped shut it off for a few minutes, restarted and stuck at 3000rpm, I thought maybe throttle linkage or the like,but no. Throttle is on the stop, no obstruction, was running great. I unplugged the 3 wire connector to the tps and idle came to normal,enough to get me off the trail and home (power was crap and shifted poorly). I replaced the tps with a new one last night set it up with a multitester and it was good,shifted normal,power was great. Stopped to fuel up today and same thing, stuck at 3000rpm when I started it. unplugged the three pin flat connector and idle is normal, shift poorly again. What the heck is causing this??
a few things i've done in the past little while:
-new motor (reman -new fuel pump and filter
-33's
-thats about it, I will post up if I remember anything.

What am I doing by unplugging the 3 pole connector?I can understand why It shifts funny and runs like a dog when unplugged. help! thanks kindy gents!

Muad'Dib
April 8th, 2008, 19:34
Have ou cleaned your throttle body? How about the IAC?

Im thinking the IAC is the culprit here.

Seems like a stupid question also, but you did adjust the TPS correctly right?

bcmaxx
April 8th, 2008, 20:02
Have ou cleaned your throttle body? How about the IAC?

Im thinking the IAC is the culprit here.

Seems like a stupid question also, but you did adjust the TPS correctly right?

unplugged and plugged in the iac while runnin,no change, even tapped on it. yes the tps was adjusted correctly as per fsm with a voltmeter and a calculator. Throttle body is spic and span.I'll try a used iac off a spare t.body in the morning.

projectTK
April 8th, 2008, 20:28
check vacuum lines. make sure tps isnt sticking. Mine does that everyonce in a while i just rev it up and it comes back down to normal idle.

bcmaxx
April 9th, 2008, 08:11
If I touch the gas it will go up and stay up. I have tried to let it run throught the high idle with no luck. anybody? this blows

Muad'Dib
April 9th, 2008, 09:19
If I touch the gas it will go up and stay up. I have tried to let it run throught the high idle with no luck. anybody? this blows

This happened to me when the IAC was sticking. Make sure the IAC cavity is clean, and try a few different IAC's. I just pick them up at the junk yard for testing purposes.


It also happened when i had some vacuum leaks that were to me hard to find. Check all your vacuum lines carefully.

Before i knew what to look for, and how to fix it.. i could usually get it to idle correctly when i would stomp on the gas till it reached about 5000 RPM's then it would go down to normal idle.

bcmaxx
April 9th, 2008, 12:43
Really weird, The new Iac did not make a difference, I am adding another ground from the motor to the firewall,Ground is new from batt to engine. I also plan on checking the grounds at the tps harness tonight.
If the tps is unplugged it will start and idle good, as soon as I plug it it it raises to 2500-3000rpm. If its is plugged in when I start it it immediatly goes high idle, if I unplug it and crack the throttle it idles down again to normal. I also brough a spare complete throttle body to work today to test out if all else fails.

bcmaxx
April 9th, 2008, 12:48
Just going through the fsm and it stated the three pin connector three pin connector supplies input to the tcu, Why in the world would unplugging it fix anything. If anything unplugging the 4 pin should effect idle right???
I'm so lost right now!

REPOXP777
April 9th, 2008, 12:58
Sounds like a bad or misadjusted TPS . Or a bad ground to the TPS . Make sure when you adj the TPS you do it from the TCU side of the TPS . This will cause all kinds of trans shifting problems with a bad or misadjusted TPS . Have you checked your intake manifold gasket ?? Good Luck .

bcmaxx
April 9th, 2008, 13:49
oh and brand new intake gasket, studs nuts and all, no leaks, good vacuum.

Oizarod115
April 9th, 2008, 15:03
if you unplug the TPS basically the computer runs a pre-planned program so it'll run like shit because it doesn't know whats actually going on, but it will at least run still.

try backprobing the TPS (the signal out and the ground wire) and with the key in the run position engine off open the throttle until it reaches 5v open and close it a few times it should raise voltage smoothly from .8 up to WFO

bcmaxx
April 9th, 2008, 15:21
if you unplug the TPS basically the computer runs a pre-planned program so it'll run like shit because it doesn't know whats actually going on, but it will at least run still.

try backprobing the TPS (the signal out and the ground wire) and with the key in the run position engine off open the throttle until it reaches 5v open and close it a few times it should raise voltage smoothly from .8 up to WFO
Sorry my internet terminology sucks what is wfo?

XJFisher
April 9th, 2008, 15:52
i have an 88 xj too, and it does that to me a lot. the only way that i can get it back down is to gas it a bit and sometimes it will come back down. if not, turn it off and wait a couple mins

bcmaxx
April 9th, 2008, 16:03
update, won't idle down at all now, even with iac, and both tps connectors unplugged. can no longer drive it now :banghead: .

89CherokeePioneer
April 9th, 2008, 16:12
Is the harness for the TPS itself clean, no corrosion? Might want to start moving wires around to see what that does.

Sensor ground by the oil dipstick, is that still attached and relatively clean?

Oizarod115
April 9th, 2008, 16:12
WFO= wide ****in' open

this is a far reach but check the PCV stuff on top of the valve cover make sure its not popped out,

and try taking the hose off the brake booster and plugging it
another far reach but maybe the brake booster is doing something funky and lettin loose makin your truck rev?

Rambopants
April 14th, 2008, 17:06
Man im having the same problem, New TPS and IAC. New wire connectors on the Male end of the wire harness going into the TPS, I have Adjusted the TPS from the both connectors and get the same problem, Start the Jeep and it goes to normal rpm then turn off and start agian it goes to 2500 +

Muad'Dib
April 14th, 2008, 18:14
Vacuum Leak?

Ecomike
April 14th, 2008, 18:44
Just going through the fsm and it stated the three pin connector three pin connector supplies input to the tcu, Why in the world would unplugging it fix anything. If anything unplugging the 4 pin should effect idle right???
I'm so lost right now!


update, won't idle down at all now, even with iac, and both tps connectors unplugged. can no longer drive it now

The IAC is wide open causing the high idle, with it disconnected the ECU can not return it to the normal idle air flow possition even if it wanted to!!!!!:shocked:

The three pin, flat connector is the engine fuel injection computer, AKA ECU. The square four pin connector is the TCU (tranny) computer.

Have you guys tested the TPS ground wires at the TPS on both sides to the battery negative ground, it should be less than one ohm, power off.

I fought this problem for 2 years before i discovered all my ground wire values were changing while the engine was running. When that happens the back voltage in the ground wires builds and the TPS voltage to the ECU builds up telling the ECU to give it gas and air (IAC)!!!!

Also, any, and I mean any small vacuum leaks, even at the valve cover gasket run the idle up!!!!! Leave no leaks untended.

Lastly, my only remaining high idle problem is a loose floor mat, The floor mat slides up against and under the gas peddle randomly!!!!!!:shiver:

stewie
April 14th, 2008, 19:28
i agree with the prior two posts on vac leaks. i had a buddys 89xj over at my house and we got to talking about vac leaks. i have used seafoam in my engine introduced through the vac system (brake booster hose) and i am familiar with the way the engine will rev when the hose is disconnected from the booster assembly- creating a vac leak. he got to looking and found a hose completely missing at the "tower" at the front of intake manafold. im not too sure where the hose was supposed to go to. when the spot on the "tower" (had more than one vac line) was covered, the rig idled beautifully, remove the obstruction (finger) and the idle would jump back up.

i would check for vac leaks. it cheep to diagnose-free- and has a realy cheep to bandaid, tape. the bandaid fix doesnt last long as the heat from the engine will screw with the adhisive. if you find a leak, tape it up if possible and keep looking for more. start at the intake manifold and follow each line out. pay attention to all connections and any oily spots on the plastic lines. after all the vac leaks have been found, check how it idles. replace the broken lines as soon as possible. when i checked my rigs vac system i was able to find 4 vac leaks and i wasnt even having any idle issues yet.

hth
stewie

bcmaxx
April 22nd, 2008, 15:09
the gremlin has returned, seems to happen when underhood temps are higher. 2500 to 3000 rpm. shut the truck off, restart with tps unplugged, then plug it back in problem solved till it happens again. I have already ran battery ground to the tps grounds. I noticed with key off all four terminals to the iac are ground, key on the 2nd and 4th are ground. Can I run battery ground to the two that are constant ground or not such a good idea?? My next plan of action:
replace the fusible link to the latch relay, run a load from the latch relay to the harness connector on the ecu, and the same for the four wires going from the ecu to the IAC. Anything I'm missing?

bcmaxx
May 6th, 2008, 19:43
calling renix experts, high idle back again!!!! starts running at 1100rpm then progresses to 2500rpm, unplug tps to trans and fixed (temporarily), NEW FINDING unplug b+latch relay and idle levels back to normal, plug it back in and high idle,and have tried swapping relays,no change. If I disconnect the battery after it cools off its good for well just about two weeks, any suggestions? the only thing left Is maybe an ecm or tcm ,I dont know if the tcm would be related. It Isn't a ground issue for all I can figure. would it be advisable to jump the wires to and from the b+ latch relay?? I'm almost lost on this one!!!


Only happens once underhood temp is up to operating temps,so I think it may be a connection/wiring harness problem, it it really feasible to run new wires off the ecm to the b+latch relay and the iac? I'm positive its the iac troubling me, getting sick of this!! help!sos!

Muad'Dib
May 6th, 2008, 20:11
calling renix experts, high idle back again!!!! starts running at 1100rpm then progresses to 2500rpm, unplug tps to trans and fixed (temporarily), NEW FINDING unplug b+latch relay and idle levels back to normal, plug it back in and high idle,and have tried swapping relays,no change. If I disconnect the battery after it cools off its good for well just about two weeks, any suggestions? the only thing left Is maybe an ecm or tcm ,I dont know if the tcm would be related. It Isn't a ground issue for all I can figure. would it be advisable to jump the wires to and from the b+ latch relay?? I'm almost lost on this one!!!


Only happens once underhood temp is up to operating temps,so I think it may be a connection/wiring harness problem, it it really feasible to run new wires off the ecm to the b+latch relay and the iac? I'm positive its the iac troubling me, getting sick of this!! help!sos!

When is the last time you replaced your o2 sensor??

bcmaxx
May 6th, 2008, 21:32
When is the last time you replaced your o2 sensor??
been a little over a year and a new motor 1 month ago

Muad'Dib
May 7th, 2008, 11:27
been a little over a year and a new motor 1 month ago

Since this problem happens when the engine is warm, and is effected when you unplug the +b latch relay (are you sure this is the one your unplugging??) then that points me to your 02 sensor. Have you ohmed out the heater element in it? Do you have a known good one that you can test with?

You know, now that i think about it more, i had a similar problem that was solved by replacing ALL of the relays that were on my Jeep with SPDT BOSCH's. That may be one inexpensive thing to try before anything else.

bcmaxx
May 7th, 2008, 17:02
Since this problem happens when the engine is warm, and is effected when you unplug the +b latch relay (are you sure this is the one your unplugging??) then that points me to your 02 sensor. Have you ohmed out the heater element in it? Do you have a known good one that you can test with?

You know, now that i think about it more, i had a similar problem that was solved by replacing ALL of the relays that were on my Jeep with SPDT BOSCH's. That may be one inexpensive thing to try before anything else.

I will try and replace them ,I have some known good ones, the b latch is the second from the firewall, no havent tested the 02 but will, I just got my hands on a fsm. thanks

bcmaxx
May 26th, 2008, 22:50
Found the problem. feel a little stupid, I went to re-check the grounds at the dipstick bolt, saw three perfectly connected grounds and noticed they were a little taught, I un hooked it pulled back the loom and found a single wire broken about four inches up covered by the loom ,since fixed it and I now have very smooth consistent idle as well as good throttle response and seems like it takes less pedal to do the job.party/celebration time.
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