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Extremely Rough Idle problem...

Twisted_Dakota

Twisted_Dakota

NAXJA Forum User
Location
Ft. Worth, TX
Ok so I finally got my jeep up and running. The Computer had crapped out on it.

Now that it runs it idles very rough and it will get to the point where its so low that it dies. If you just let the jeep sit and idle by itself the rpms fluctuate but once you rev it up a bit thats when the rpms get so low it dies.

I cleaned out the throttle body today as well as the intake manifold, and it seems to kinda helped a bit but the idle is still very rough.


Jeep is 1988 4.0 with 250,000 miles.


Evan.
 
try a tune up, and check out your EGR... my 89 started doing this, never actually died but rpms went off the scale and i gave it gas to keep it from stallin out (manual tranny)

but i'm not sure if it was the EGR doin it or the tune-up cause i plugged the line to the egr off and did a tune up and it went away. i've since replaced the EGR and it hasn't done it again in 2 months
 
tune up has been done already. I guess I will check the EGR.
 
how long did it sit? bad gas? .... dosent it need to relearn its idle,alot of jeep/chry. need to relearn ldle after a dead batt,or pcm change.
 
98XJeep said:
how long did it sit? bad gas? .... dosent it need to relearn its idle,alot of jeep/chry. need to relearn ldle after a dead batt,or pcm change.
Click to expand...


it had been sitting for a year and a half and the first thing I did after buying it was drain the tank and have it cleaned.

As for the relearning part I am not sure.

The whole history since I bought this jeep has been on here in two different threads but whent he site crashed it was lost.

Quite a bit has been replaced on this jeep and more is on the way.
 
98XJeep said:
how long did it sit? bad gas? .... dosent it need to relearn its idle,alot of jeep/chry. need to relearn ldle after a dead batt,or pcm change.
Click to expand...

nah, it won't store anything anyways, the RENIX system doesn't store codes or anything, in fact... i dont think we have CELs... never seen one anyways.

the EGR will be bolted near the throttle body, on the side of the intake. and it'll have a little black UFO lookin thing attached to it with 3 vacuum lines.
 
Oizarod115 said:
nah, it won't store anything anyways, the RENIX system doesn't store codes or anything, in fact... i dont think we have CELs... never seen one anyways.

the EGR will be bolted near the throttle body, on the side of the intake. and it'll have a little black UFO lookin thing attached to it with 3 vacuum lines.
Click to expand...

Ok. Yeah the renix jeeps dont have CEL's really makes shit hard to figure out.
 
Man...12 posts and nobody said MAP SENSOR. Check your MAP sensor. Also, it could just be that the vacuum line going to the MAP sensor slipped off. Mine did that after doing some work in the engine bay, I unknowingly knocked it off and it did exactly what you are describing. The MAP sensor sits on the fire wall, looking into the engine bay just to the upper right of the back of the valve cover. It's a little box with a vacuum line coming into the bottom of it. Check it out.
 
my '87 had a similar issue. after much troubleshooting it looked like the egr was stuck open. i pulled it off, and it had a little chunk of carbon stuck right on the pintle seat keeping the valve from closing all the way. cleaned it out, put on a new gasket, and it's been fine for about a year now.
 
After all my prior lecture threads, no one has mentioned the Renix grounds!!!:twak: Check the grounds, all of them, any ground wire reading more than 1 ohm to the negative battery post is a problem. Check the grounds with the power, ignition OFF. Check the TPS ground wire too, disconnect the TPS sensor and check it from the harness to the negative battery post. Needs to be less than 1 ohm. If any of the grounds or sensor conectors, like the TPS connector are loose or dirty, they will change the ground resistance with heat and vibration which drive the ECU nuts. Check the engine grounds, all of them at the oil dip stick to the battery and fire wall, and on the passenger side check the ground from the rear of engine head to the firewall. Check the battery running, voltage too.

If all the sensors, O2, MAP, TPS, grounds, the C-101 bulkhead connector, plugs, plug wires, HV coil, etc check out, then check the compression! Low compression on one or more cylinders will make the idle rough, but a low idle is probably a ground problem or TPS problem or both. You could have separate idle and rough engine problems.
 
Oizarod115 said:
nah, it won't store anything anyways, the RENIX system doesn't store codes or anything, in fact... i dont think we have CELs... never seen one anyways.

the EGR will be bolted near the throttle body, on the side of the intake. and it'll have a little black UFO lookin thing attached to it with 3 vacuum lines.
Click to expand...

Contrary to current folk lore, the Renix ECU and the TCU for that matter, do store some limited recent sensor value info. It does sometimes help to clear the old sensor memory values by multiple restarts and drive cycles or by disconecting the battery for a while.
 
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