stutters only when cold (idles around 5-600)

so once the jeep is "warm" it idles at 750...but when first starting it...it revs to 2000 (at first) then drop right down to about 900...then a few seconds later starts dipping to 500...and some time under that almost stalling.

so i can only guess it has to do with open loop? posibly the o2 is bad (no heating up, if they are heated)

other than that it runs fine....seems like it is slightly down on the power (unff) side though

Uhhh... Hellllllo! What year please?!

AJPulley said:

Uhhh... Hellllllo! What year please?!

Click to expand...

um...maybee a 88'XJ? lol

i should specify that it a 88' 4.0 renix with a pukegoat, 4x4

88'XJ said:

um...maybee a 88'XJ? lol

Click to expand...

All right, that's better.

Now, what have you done so far to it and what have you checked? When did it start?

Check the coolant temp sensor for the PCM. It's located in the lower radiator hose I believe.

well..i got this jeep for $100..did a clutch, shock, and exhaust.

previos ower had all maintance records (original owner) and the jeep has 128,000 miles...looks to have new radiator and w/p.

i cleaned the crap out of the t.b. and that helped a bit (was stuttering all the time..and had a low idle)

had new plugs/wires...i did a cap and rotor.

thats stuff i have "checked"

now whats this temp sensor? how do i check it, i know the jeep runs "cool" (the line under 210...never goes over 210)

thanks for the help

As an owner of a 88 XJ I recommend you have the throttle body cleaned. Over time mung can get in the Idle air controller and mess with things. You will need to remove the throttle body with cleaner, make sure not to spray the electronics.

Make sure you spray down the square hold next the the large opening, spray the idle air passage until the cleaner comes out clean. Also use a brass brush to get the mung off the back side of the butterfly.

When done cleaning then reinstall with a new gasket. That is where i'd start. I took my XJ to the dealer and had the guy clean it, he even let me watch him. Once done he hooked up the test set and made sure everything was in spec, even recalibrated the TPS. Best 1.0 hour of dealer labor I ever paid for.

It just dawned on me... are you aware that the quick idle up-then-down is normal for these engines? Is it that, or the almost stalling issue you are concerned about? From what you describe, the IAC motor is working, and the idle seems OK at 750 RPM. 500 after starting a cold engine also sounds normal. But, the almost stalling might just still be carbon. If you lean over the driver's side fender, and look at the top of the TB without the air tube on, there is a small hole at about six o'clock to the throtle bore and plate. This is an idle air bypass and it should have vacuum if you stick your finger over it. Squirt some cleaner in that small hole too. Also, remove the IAC motor, and take a rag and clean off/out what you can. There is a metal tappered valve that will be attached to it when you pull it out.

Next, after the engine is warm, shut it down and unplug the IAC motor. You should be able to restart the engine without it idling up-then-down. The engine should also run about 500-700 RPM. This helps verify base idle without the assistance of the IAC.

Let me know what happens.

Oh, the tempurature should run at 190, so that's OK that it doesn't go to the 210 mark.

I was just about to post this same problem ('88 MJ 4.0L auto). I have the exact same symptom, and it too started with a low idle. It starts and idles great for about 10 seconds, but then the idle starts to slowly dive toward 0 for a few seconds (shakes) and sometimes dies, but when it is warm, it idles normal. Cleaned, tightened, tested, adjusted to spec, and even started to replace sensors that I knew were good. Please find a cure for the Renix!!! (p.s. mine smells plenty rich at cold startup, but plugs look good). I suspected CPS at first, but replaced and no change. Also, suspected CTS, but it seems to be in spec 3300 ohm cold, and 250-ish warm. AJPulley, good post. Thanks for the info. I checked my idle air bypass and it didn't pull much if any vacuum (i cleaned it). Should I pull that little metal plug cover off and adjust?