monst3r

I had another post but I accidentally posted in the wrong place!

Anyway my 1987 Cherokee Chief, 5speed has some idle issues, I have done a lot to try to solve it but I am not sure where to go to next. It idles at about 600RPM cold and if the throttle is hit when cold it goes way down when it brings the revs down almost to I would say 200RPM. When she is warm she idles at about 550 RPM and does not have the rev issue, seems to come down normally. I would love to fix the cold idle issue and bring the idle up in general, 550 is too low! It does move slightly up and down maybe 50RPM or so when just sitting idling

I did have a high idle before (1200) and adjusted the throttle butterfly to stock using Cruisers tips, then adjusted TPS again. Once I did this the idle came down but unfortunately now its to far down. I should mention the PO disconnected the EGR and plugged the vacuum lines, if this is relevant.

Things done:

• Cruiser Renix Tips done: 1,2,3,4,5,6,7,8,9,11,14,18
• Checked and tightened intake manifold/exhaust manifold.
• Checked for vacuum leaks with carb cleaner
• Replaced Plugs and wires
• Replaced Coil with used one due to starting issues
• Replaced CPS, again starting issues
• Compression test results dry cyl1-6: 120,125,125,120,130

Any help is appreciated! Maybe it's time to replace the IAC? I cleaned it pretty good with sensor cleaner (carefully I should add) and no matter how much I cleaned it there was some burnt on residue.

DFlintstone

Well, see what others say. My 02 is yea, IAC related. I removed and cleaned mine a few times over an occiacional high idle, then figured out it was actually my connection at the plug. I think the socket facing up got water in there at some point. Sort of hard to see in there! You might try spraying there well with CRC electronic cleaner, work the plug in and out repeat..

"no matter how much I cleaned it there was some burnt on residue" last time I did it I scraped to shiny metal with my fingernail.

The EGR shouldn't be an issue. TPS could be! (maybe double check, engine side of course)

monst3r

I will spray the crap out of it tomorrow. See what happens.

I did test the TPS multiple times I have it set perfectly to .82 which is 17% of my reference. Wish I just had another IAC to test it with haha.

cruiser54

Great job so far. No mention of O2 sensor replacement?

I have become an advocate of Tip 27 after seeing the results on the XJ that was used in my write-up.

monst3r

Could the 02 sensor really cause such a low idle though? Is there a method to test it?

I really am tempted to do the c101 connector, might just need to buck up and do it. I've been avoiding it like the plague. Maybe this weekend.

cruiser54

Yes, it can cause low idle issues.

It is testable.

Do the C101 elimination first. easy to do.

DFlintstone

When my Renix 02 was stone dead, the idle would fluctuate about every 20 secs. It would slow, nearly die, speed up a few seconds, then repeat.

monst3r

Yeah mine not is quite that bad. Is there an easy way to test the O2 sensor?

I did the c101 delete now, well it was fun but it did not help whatsoever still has the same symptoms (low idle and when cold idle goes so low it stumbles, 100rpm or less for a second or so). What is the idle supposed to be? It idles at about 550 but it goes up and down 50-100 over and over, it does smell like it has a slight over fueling, with a small backfire now and again when hitting the throttle but the previous owner put in a glass back exhaust which has a hole in the pipe just before so this is possibly that problem.

Also cleaned the IAT it was pretty filthy, funny enough cleaning it got rid of this weird stumble I had when turning the truck off.

JamDeeper

Subbed. I wanna see if you fix it. My 89 will bounce off the "0" rpm bump sometimes, it idles so low. Like you said, after it warms up, it's about 600 to 800. The day I bought it I noticed. But it doesn't bother me. I still have great throttle response and it's never actually died.

Is there a reason this is "bad" or you'd have to fix it?

monst3r

Yeah mine has never died either. For myself it just bugs me that's why I want to fix it cause other then that she runs fine. I would hate to write it off as a "Jeep" thing haha, but she is almost 30 years old.

cruiser54

How many of my Tips have you completed on that old Renix?

monst3r

Things done:
Cruiser Renix Tips done: 1,2,3,4,5,6,7,8,9,11,14,18 and now 27

I think I am becoming one with your list haha I even have it printed out in the Jeep.

cruiser54

Time to visit O2 sensor.

BTW, I'm proud of you. LOL.

884x4

At my school(UTI auto/diesel) we have a program called All Data.
It shows basically all the manufacturers specs and tolerances. It also shows recalls and service bulletins.
So for fun one day I decide to look at the bulletins for 88 jeep cherokees. It showed they had a problem with 02 sensors going bad with minimal mileage. I thought this was interesting and thought I would share..lol

monst3r

Appreciate it. I will replace the 02 sensor but it's going to be awhile before I get it because I am ordering it from the US. In canada it's over $80 and I need to order a bunch more stuff from RockAuto.

I will post back with my results in a few weeks!