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Rough idle on a 90' RENIX

xjtrailrider

NAXJA Forum User
NAXJA Member
Location
Roanoke VA
Its not a Ignition problem, it just seems to labor like it is running too rich. If I unplug any of the many vacuum lines the idle picks up and smooths out. It is also stumbling a little just off idle.

Its a 90' 4.0(newly rebuilt, its only been in the Jeep one day), AW4

It runs fine otherwise.

And yes I have searched, my search feature does not work properly.

I forgot to mention that the O2 sensor is brand new, TB and intake has been cleaned in a ultrasonic cleaner and looks like new inside and out, the FI's have been cleaned/rebuilt/tested and one was replaced.
 
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how about the IAC?
 
Are the CCV tubes all new and in good shape? If not, NAPA sells them under Echlin P/N, ~$50 for the set. Also check the movement on the EGR valve. Some folks have seen great results with the Renix by just cleaning and checking the sensors and grounds.
 
Yes, I forgot to mention that all of the CCV and vacuum hoses/plumbing is new. I also have new cap/rotor/plugs/wires. I've checked/cleaned the coil connections to IM. The EGR is moving when I give it some throttle, and seems to function O.K.

I think my problem is with the EGR solonoid, when I unplug the double vacuum connection(the one with the vent on it) the idle smooths out but doesn't race up like it does when I just unplug a vacuume line.

Does this make sense? Is it the solonoid or could it be the EGR?
 
I also wan't to add that while I was doing a "mock" state safety inspection on the Jeep I covered the tailpipe with a rag to check for exhaust leaks and it killed the motor, tried it again for kicks....killed the motor! I think I'm getting closer to a EGR prob.

Anybody got an opinion on this?
 
Just an update, I plugged the vacuume to the EGR, the idle smoothed out a lot. Then I adjusted the small screw(turned it in) at the base of the TB(it faces the fender) and it smoothed out some more. I've checked the intake bolts for tightness and all good there. Still seems to be a slight vacuume leak, so I'm still looking.

Its way better than it was.

Its almost there, but not yet!

It seems to have just a little fluctuation after warm-up.

Anybody else have any ideas?
 
if ur looking for a leak, make sure u check the hardlines and the lines going to the vacuum can(in bumper).
 
I'll check that vacuum can tomorrow, right now its running fine other than a little "hunt" at idle and a slight stumble just off idle.

Thanks 87manche for the links, I down loaded all of them!

But as my luck goes the 16 year old starter is going, I have to tap it with a hammer to get it to kick the bendix.

Guess I'll pick up a starter also!
 
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You were going after EGR which gives the problems you were reporting, did you check it all out and move on to vacuum leaks? With ReNix its almost always a sensor, and your probs all pointed to EGR, BTW, I had a vacuum leak in my EGR (the bell shaped deal on manifold) and that gave me my bump idle and rough take off from the start, You pinpointed it when you pulled the vacuum to the EGR. Just wondering if you found a problem there or not and moved on...Good Luck
 
It idles, on a scale of 1-10, about an 8. O.K. but not great.

Disconnecting the EGR made the biggest difference. Since we dont have emissions inspection in SW VA, I'm going to just leave it plugged.

I think I've settled any vacuum issues and I'm looking toward fuel delivery, due to the long cranks that it takes to start it(about 5 sec.).

I may have a leaky injector. After it sits for about an hour, there is very little pressure on the rail.

It drives absolutley fine, just a slightly rough idle and a little hard to start.

When the engine is cold, I'm going to pull the fuel rail with the injectors, pressure them up and see if they leak.

I'll keep you informed, and thanks for all the help!
 
The injectors aren't leaking so it must be the check valve at the pump. I don't have a fuel pressure guage to check the regulator, but removing the vacuum and plugging it doesn't seem to affect idle at all.
 
If the injectors are holding pressure try checking the Fuel Pressure Regulator at the front of the rail, (looks like an old style fuel filter with a vacumn line running into it) Check the vacuum into it and where that vacuum runs to. As for a renix about 5 seconds is about as fast as you are ever gonna get it to crank over, I have had mine for 18 yrs, and its always taken 5 seconds to crank over, The Renix system has to do two revolutions to "report in" all the sensors and then it fires off. (that is the simplistic way of saying it so no flames) Good Luck,
 
Thanks for that info XJING. This is my first RENIX XJ, I have 3 others,95', 96', 00'. This Jeep was bought new by my Dad. It got away from me when he died, I just recently found it and I'm doing a resto on it.

I pulled the vacuum on the reg. at idle and with the vacuum line plugged the idle didn't change any.

Its good to know that the long crank is normal.

I'm fairly happy with the idle and very happy with the way the newly rebuilt 4.0 is running

I may be able to blame the new valves and reworked head for some of the rough idle. Its also been bored 40 over and decked 15. The head was also shaved. It could be the slightly higher compression ratio working against me?
 
When its time for a Crank position sensor get a high altitude one, cured a bit of off the start roughness after I tweeked my head. (got that mod from an old jeep dude) of course I live at sea level, and it was the same price of the stock one but the slight advance in timing helped that very little bit, Heres a site I send every Renix person to. The electical upgrades are the greatest, will cut down on crank time a bit as well.( or it just cranks faster so you dont notice the 2 revolutions) Check out all the mods he has taken the time to put on the web. its worth it. good luck
http://www.olypen.com/craigh/tech.htm
 
Just to update and to help those who may search later.

It was the TPS. Even though I marked it and put it back on correctly(this XJ wasn't running when I bought it so someone had monkeyed it before me), it was still out of adjustment and has a dead spot. Just a simple adjustment helped out tremendously.

I still cannot get the TPS to fully disengage from the throttle linkage, even adjusted all the way out it is still touching and is slightly moved by the throttle.

I am going to get a new TPS and possibly adjust the throttle tab to correct the TPS adjustment.

I feel that the rough idle was caused by the TPS sensing it had more throttle than it actually had and was delivering more fuel because of it.

Thanks for everyone's help.
 
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