Renix Idle Issue *Video*

>>>>>>>>>>>>CLICK HERE FOR VID<<<<<<<<<<<<

So i have been having a idle issue with the wonderful renix system we know and love so much :helpme:

What happens is it starts fine (it misses a bit, but overall its smooth) and then after a while (about 33 seconds in the youtube vid ^^^) it will act like its going to die, and then catch itself, and then do that over and over until i drive it for a while and the engine is at operating temp. The idle is also jumpy and inconsistent all the time, especially when its cold.

Replaced List:
O2 Sensor
Map sensor
CTS
Knock Sensor
TPS (adjusted)
IAC
Neg. Batt Cable
EGR Valve
CPS
Neon 703 injectors with new o rings, filters, and ultrasonically cleaned

Checked list:
MAT (good... at least at room temp it is)
CTS (good... at least at room temp it is)
ICM contacts cleaned at connectors and coil clips
All my grounds are clean/ new (showing around .2ohms)
Soldered in a extra ground wire at engine wiring harness just to be safe
NO VAC LEAKS!!!!
As far as i can tell the EGR is working.


My engine was rebuilt around 15K ago, and when i rebuilt it i cleaned the TB and intake manifold inside and out to new condition. It was having this weird idle issue even before i bought it. Its just gotten worse over time.

Question: Could the computer be the cause of this problem? yesterday i was bored so i took the computer apart and i couldn't tell that anything was loose, or burned, or i dunno... i didn't really know what i was looking at or for, i'm no computer genius haha.

Also would a FPR cause problems like this?

Please help, otherwise my jeep runs great, its just kind of frustrating, and its getting worse as the weeks go on.

I was having much the same issues with mine, seemed to be multiple issues and was most apparent at operating temperature, the first time.
A small vacuum leak, mine turned out to be a loose intake manifold. My guess is the vacuum leak was minor , but big enough to cause an air fuel conflict, the ECU tried to (unsuccessfully) compensate for.
I also had a short in the heater wire for my O2 sensor.
And I eventually found a loose splice in the wiring harness, it was the ground for most of my sensors (TPS), it ohmed good but was way loose anyway. I noticed a marked improvement after some solder. Something else soldering that splice seemed to all but eliminate was the typical Renix hot start, when the motor sometimes surges to 1700 (or higher) RPM when starting hot. It didn't completely eliminate it, but made it really rare. I'm guessing something was taking an odd path to ground and messing up my TPS values.
Another time when I was having that idle cycle like you have, it was battery related and the IAC was a bit sticky. When I first started up, my weak battery took much of the juice form the charging system and there didn't seem to be enough left over to operate the IAC properly, it was slow and sticky. If I spray oiled the IAC it would help, but it went away after a new battery.
I also cleaned out the idle air adjustment, "not" the throttle plate adjuster. There is a capped and sealed air bypass for the TB, that many people don't know exists. Mine was full of crap.
I wish I could give you a one fix answer, but my best guess is many things can cause the idle to cycle like that.

8Mud said:

I was having much the same issues with mine, seemed to be multiple issues and was most apparent at operating temperature, the first time.
A small vacuum leak, mine turned out to be a loose intake manifold. My guess is the vacuum leak was minor , but big enough to cause an air fuel conflict, the ECU tried to (unsuccessfully) compensate for.
I also had a short in the heater wire for my O2 sensor.
And I eventually found a loose splice in the wiring harness, it was the ground for most of my sensors (TPS), it ohmed good but was way loose anyway. I noticed a marked improvement after some solder. Something else soldering that splice seemed to all but eliminate was the typical Renix hot start, when the motor sometimes surges to 1700 (or higher) RPM when starting hot. It didn't completely eliminate it, but made it really rare. I'm guessing something was taking an odd path to ground and messing up my TPS values.
Another time when I was having that idle cycle like you have, it was battery related and the IAC was a bit sticky. When I first started up, my weak battery took much of the juice form the charging system and there didn't seem to be enough left over to operate the IAC properly, it was slow and sticky. If I spray oiled the IAC it would help, but it went away after a new battery.
I also cleaned out the idle air adjustment, "not" the throttle plate adjuster. There is a capped and sealed air bypass for the TB, that many people don't know exists. Mine was full of crap.
I wish I could give you a one fix answer, but my best guess is many things can cause the idle to cycle like that.

Click to expand...

Thanks for the reply. I'll try and re torque the intake manifold bolts again. They were at spec just a little over a year ago when i rebuilt the engine, but thats not to say they could have worked loose i guess. My battery is new, and it cranks very strong, but i could see how a weak battery could cause issues with the IAC. Where is this idle air adjustment bypass thing?

Also my jeep revs up to 1700 or so rpm every time it starts, hot or cold. Is that not normal?

Also how did you check to see if your heater wire for the O2 sensor had a short?

goneboating06 said:

Thanks for the reply. I'll try and re torque the intake manifold bolts again. They were at spec just a little over a year ago when i rebuilt the engine, but thats not to say they could have worked loose i guess. My battery is new, and it cranks very strong, but i could see how a weak battery could cause issues with the IAC. Where is this idle air adjustment bypass thing?

Also my jeep revs up to 1700 or so rpm every time it starts, hot or cold. Is that not normal?

Click to expand...

The Renix hot start isn't normal you'll know when it happens, it idles up to way above normal and hangs there a few beats too long.

Sometimes the idle air bypass is screwed down tight closed, sometimes it isn't, it depends on the factory adjustment. I counted the turns when I took mine out, cleaned it and reinstalled it the same number of turns, put a dab of silicon on the end so it doesn't back out.

goneboating06 said:

Also how did you check to see if your heater wire for the O2 sensor had a short?

Click to expand...

For me it was kind of obvious the wires were melted onto the exhaust manifold. You can volt test at the O2 sensor, the orange wire.
Going hunting catch you later.

Speaking of grounds, how are the 3 or 4 at the dipstick tube stud? Is there fresh engine paint under them? Never hurts to run a ground wire from that stud to the passenger inner fender or directly to the negative post of the battery. All of those grounds are very critical.

8 Mud, i was always wondering what that was. Good to know..... Thanks

8Mud said:

For me it was kind of obvious the wires were melted onto the exhaust manifold. You can volt test at the O2 sensor, the orange wire.
Going hunting catch you later.

Click to expand...

Oh haha melted wires are pretty obvious. I just went out and checked the voltage at the heater wire, and its reading about 12.5 volts with engine off, and 14 with it running. Then one of the black wires has 5.03 volts. The ground tests good as far as i can tell.

cruiser54 said:

Speaking of grounds, how are the 3 or 4 at the dipstick tube stud? Is there fresh engine paint under them? Never hurts to run a ground wire from that stud to the passenger inner fender or directly to the negative post of the battery. All of those grounds are very critical.

Click to expand...

I have checked and rechecked that post for any paint or corrosion. I cleaned up the connections, and i even ran a new neg batt cable to that stud. I also soldered in a new wire to the part inside the harness where all the grounds meet, and then i grounded it to the firewall. I also tested all the ground wires and they are about .01-.02 ohms of resistance.

I keep a Package of short pieces of rubber tubing plugged with screws, I stop up every vacuum port on the manifold except the fuel regulator, the MAP and the brake booster. If I notice a difference, I replace the lines one at a time and listen for when the idle changes. Vacuum leaks at connections at the ends of the manifold tend to trigger that, what I call "hunt at idle" syndrome more than vacuum connections near the center of the intake.
I periodically re check my manifold bolts, I always seem to find some loose. Be real careful of the end studs, I usually leave them, it rarely leaks there anyway.
You should also test the flat (three pole) connector side of the TPS and test for grounds on the TPS side of the connector. I've found significant resistance in the connector itself on occasion.
Have you searched and checked out the "Renix files" yet, EcoMike did a good job of troubleshooting the O2 sensor.