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Low Idle Renix Questions

C

ctavel90xj

NAXJA Forum User
Location
Atlanta
I was tuning up my new to me Cherokee, replaced the plugs (correctly gapped), wires, distributor cap, rotor, idler pulley, and o2 sensor. Now the engine idles albeit smoother than it ever has before, at 200ish RPM. On start-up it does the normal jump to 1700 or so and then drops to 700 then slowly makes its way down to 200ish (right above the first hash mark).

Anyone got any tips as to what might be causing this? Thanks
 
I have the same issue with my 90. Its all new, newly rebuilt 4.0, all new sensors/injectors you name it, the whole Jeep is new from front to back.

I have not been able to correct it. I can bend the throttle tab and get it to idle higher but as soon as I adjust the TPS(new from dealer) it just slows back down to 300rpm. Its really bad if I have the lights on, defrost/ac on, and fan(HVAC) turned up then both of my electric fans cut on(removed the mechanical), it tanks completely out and idles like an old John Deere 2 cylinder.

If you figure it out, post up!
 
Low idle is normally caused by a dirty IAC and the cavity it mounts into, or a bad IAC.

A vacuum leak causes a high idle, not low.
 
ive got an 89 xj and it has an adjustment for idle. right where the throttle plate sits at an idle is a screw, pushing the plate further away ( faster idle) or bringing it closer ( lower idle)
 
korn9613 said:
ive got an 89 xj and it has an adjustment for idle. right where the throttle plate sits at an idle is a screw, pushing the plate further away ( faster idle) or bringing it closer ( lower idle)
Click to expand...

That's not for setting the idle. That screw should be backed out il the butterfly is totally closed. Then it should be slowly turned in til the butterfly just begins to move. It's there to keep the hard steel butterfly from beating itself into the soft material of the throttle body, not for idle speed adjustment. Just as bending the tab is not to be used for idle adjustment. Old man offers good advice here.^^^^^^^
 
I tried the IAC, its new from the dealer and the TB has been soaked and thoroughly cleaned with no difference in the idle.

I think mine is more of a ECU issue, no matter what I do to correct the idle(short of creating a vac leak) it re-adjusts itself back to 300rpm.

This problem nags the crap out of me, hopefully we can solve it.
 
My 89 dose the same thing, but it also revs up and won't come back down it goes up to about 2500. That's with it in neutral and in gear its around 15 to 1800. After I shut it off. A few times it idels ok and then idels back down around 300. I hate it . I just built the motor and switch everything. Any ideas on that?
 
rockcrusher said:
My 89 dose the same thing, but it also revs up and won't come back down it goes up to about 2500. That's with it in neutral and in gear its around 15 to 1800. After I shut it off. A few times it idels ok and then idels back down around 300. I hate it . I just built the motor and switch everything. Any ideas on that?
Click to expand...

That sounds like a bad "latch relay" or IAC
 
rockcrusher said:
My 89 dose the same thing, but it also revs up and won't come back down it goes up to about 2500. That's with it in neutral and in gear its around 15 to 1800. After I shut it off. A few times it idels ok and then idels back down around 300. I hate it . I just built the motor and switch everything. Any ideas on that?
Click to expand...

Good possibility it's a bad TPS causing idle flare. Bad engine compartment grounds can contribute to this also. On your new engine, did you scrape the fresh new paint from the dipstick tube stud when you put the ground wires back on?
 
xjtrailrider said:
I tried the IAC, its new from the dealer and the TB has been soaked and thoroughly cleaned with no difference in the idle.

I think mine is more of a ECU issue, no matter what I do to correct the idle(short of creating a vac leak) it re-adjusts itself back to 300rpm.

This problem nags the crap out of me, hopefully we can solve it.
Click to expand...

Is your CCV system clogged with crud?
 
Are you sure it's really idling at 200 rpm? On my XJ ('89), the first hash mark on the tach is 500 rpm (I think, since it's a heavier mark...like the ones higher up half way between even 1,000's). Mine idles right above the first hash mark when warm and in drive.

I also had the high idle problem after start-up...wouldn't go down until it was shut off then re-started. The problem was especially frequent when it was cold outside (less than 20 degrees). Cleaning IAC cured it.
 
Flyfisher said:
Are you sure it's really idling at 200 rpm? On my XJ ('89), the first hash mark on the tach is 500 rpm (I think, since it's a heavier mark...like the ones higher up half way between even 1,000's). Mine idles right above the first hash mark when warm and in drive.
Click to expand...

x2. the first hash is 500 RPM, not 250. i doubt the engine would even run at 250 considering it needs to reach 300 RPM for the computer to tell the engine to fire when starting up.
 
My 87 ran at 200-250 rpm two different times. First time was when I connected the O2 sensor connectors backwards, second time was when I connected the TPS sensor backwards. Both on my 87. The clips were gone, so it was, is possible to connect them back wards on mine. The ABC on the two halves helped me match them back up the right way. Low idle went away.
 
90xj06 said:
check your map sensor. you might have knocked the hose off. it will idle like you describe or barely stay running.
Click to expand...

Disconnected the MAP sensor vac hose usually makes a noticeable sucking sound, and IIRC raises the idle due to the vacuum leak, and runs like a POS, puking and backfiring on acceleration?
 
Ecomike said:
My 87 ran at 200-250 rpm two different times. First time was when I connected the O2 sensor connectors backwards, second time was when I connected the TPS sensor backwards. Both on my 87. The clips were gone, so it was, is possible to connect them back wards on mine. The ABC on the two halves helped me match them back up the right way. Low idle went away.
Click to expand...


I'll check the O2, that is a possibility and if thats what it is I owe you a beer or six:D


cruiser54 said:
Is your CCV system clogged with crud?
Click to expand...

Its all new, like the rest of the Jeep. I'm running a 96 valve cover and 96 CCV system
 
I do need to change my o2 and I need to chnge my tps. And ill check my ground, do you think that adding another. Ground from the motor to the chasis would help at all? Thanks not trying to hijack but I was just having the same type of problem. Thought it was a good idea to keep it all together instead of starting another thread.
 
I had this in the waggy for a long time. Changed every damn sensor on the engine literally. Also put in new ford injectors. When that didnt work I started looking at the wiring. Check the input voltage on the map sensor and the TPS, both should be at or very near 5v. Check the resistance to the negative post on the battery from both sensor grounds. Should be very little to none. I ended up cleaning all my grounds, adding a 4/0 ground from battery to body, cleaning every connector on every sensor, replacing a few bad ones, fixing a couple of corroded wires here and there and now it is running much much better. I still can't say it is perfect, but it is much better. Renix are extremely finicky when it comes to grounds so check every one you can find and then find the ones you cant see and check those and then add a couple and check those too and then re check them all and add 37 more and you should be good to go!!
 
Refresh all your grounds and add some. Good advice above from Curtis H. I wouldn't spend another minute or another dime on your problem til the " ground work" is done. Pun intended.
 
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