The RENIX low Idle chronicles, long read!

[Super mud]

It unfixed itself....again. I have a new ECU that I'm going to try next.

Uncle Bob was just an imaginary person to blame the improper throttle stop adjustment on haha!

I see. Mine is currently adjusted to keep it from dying but did not have a problem till I bored the TB. Think it could be that torx plug I messed with or the IAC. It previously idled at 600rpm, now at 400rpm opened up. Also will not step up for warmup. Straight to 400rpm. So I'm thinking electrical

 

[bails85]

Have u checked for intake leaks. Spray some ether around the gasket areas while it is running. It's worth a shot.

 

[Ecomike]

Have u checked for intake leaks. Spray some ether around the gasket areas while it is running. It's worth a shot.

Intake leaks cause high idles, not low idles.

 

[xjtrailrider]

I got around to installing my known good RENIX ECU today. Just a recap, I was given this ECU by the local Jeep Dealer. They used it for diagnostics purposes.

Besides that top screw being a PITA to get to to change it out, my idle is no different now than it was with the old ECU!

So if its not the ECU, all of my grounds are very good, all of my sensors and outputs are new, what the hell is causing my low chronic low idle?

My idle will drop to as low as 300rpm when the alternator is being taxed and the AC is on. It barely chugs along

The Jeep runs perfect otherwise.

 

[cruiser54]

I got around to installing my known good RENIX ECU today. Just a recap, I was given this ECU by the local Jeep Dealer. They used it for diagnostics purposes.

Besides that top screw being a PITA to get to to change it out, my idle is no different now than it was with the old ECU!

So if its not the ECU, all of my grounds are very good, all of my sensors and outputs are new, what the hell is causing my low chronic low idle?

My idle will drop to as low as 300rpm when the alternator is being taxed and the AC is on. It barely chugs along

The Jeep runs perfect otherwise.

You've got the butterfly adjusted properly, correct?

If so, adjust the Torx screw on the driver's side of the TB to obtain about 900 RPM in neutral or Park.

 

[xjtrailrider]

You've got the butterfly adjusted properly, correct?

If so, adjust the Torx screw on the driver's side of the TB to obtain about 900 RPM in neutral or Park.

Yes the butterfly is adjusted right. The torx screw on the TB can be moved all the way in or out without any change in the idle!

My TB was ultrasonically cleaned when I rebuilt the engine back in 09. It has maybe 30k on it since the cleaning.

 

[cruiser54]

How clean is the TB now?

 

[xjtrailrider]

How clean is the TB now?

Last time I looked it was still relatively clean. I'm installing the Spectre cowl intake tomorrow and tuning it up with a new ACCEL cap/rotor and some new NGK's

I will take a good look at the TB when I'm in there

 

[Ecomike]

IAC on should increase the idle 200 rpm (apx), if it is not, it makes me wonder if the ECU is getting a signal that the AC clutch has engaged? You might dig through the wiring to see if their is an ECU input from the clutch powering on, and then track down that wire an look for a fault there as part of the answer.

Mine 87 has decided that it likes 550 rpm in Drive ever since I found and fixed the last miss which was a bad fuel injector connection, that worked part time. But it idles smother than it ever did since I bought it 6-7 years ago, so I am leaving it alone.

 

[cruiser54]

It bugs me that you can move that Torx screw and idle doesn't change. Sure the TB butterfly isn' open a bit?

 

[Crashsector]

I had similar issues and really started tracking down the cause when I was able to use a scanner to read all of the sensor inputs in real values. See if anyone near you has an old Snap On scanner with the Jeep 1 cartridge and harness. It is going to save you so much time troubleshooting.

For the record my problem was a bad EGR valve, but it sounds like you already counted that out.

Good luck!

--Andy

 

[Ecomike]

It bugs me that you can move that Torx screw and idle doesn't change. Sure the TB butterfly isn' open a bit?

I think one of mine is the same way, but I forget, been a long time since I fiddled with one.

 

[xjtrailrider]

I checked the TB today and although some carbon was present, there was not any "gunk" in the TB at all.

I tuned it up and installed the Spectre kit, still no change in idle. I didn't expect any either though.

 

[Ecomike]

Hard to tell what you have there with those non OEM mods on there. Have you tried using a larger orifice on the CCV rear line from the valve cover to the intake manifold? Those mods you made may have reduced the flow there?

 

[xjtrailrider]

Hard to tell what you have there with those non OEM mods on there. Have you tried using a larger orifice on the CCV rear line from the valve cover to the intake manifold? Those mods you made may have reduced the flow there?

That's a good point. I'm running the CCV system from a 96 XJ 4.0, I basically just ordered new elbows for the 96 model since that cover is off of a 96 model XJ.

 

[Ecomike]

I experimented with different orifice sizes on mine at one time. It can affect the idle speed!

 

[xjtrailrider]

I experimented with different orifice sizes on mine at one time. It can affect the idle speed!

That's interesting. Should I go bigger and by how much?

 

[xjtrailrider]

Hard to tell what you have there with those non OEM mods on there. Have you tried using a larger orifice on the CCV rear line from the valve cover to the intake manifold? Those mods you made may have reduced the flow there?

Mike, things look modded but trust me its all stock other than the cowl intake. The EGR is plumbed in but not with the plastic tubing but with 2-cycle fuel line. The CCV is plumbed into the stock location on the manifold.
The only plastic line left is between the TB and MAP and the manifold and FPR.

The evap goes int to the elbow of the cowl intake with vacuum hose. It was nice to eliminate 3' of plastic tubing for that.

EDIT; I forgot to mention that the TPS and CPS are hard wired in. I no longer trusted the connectors. Those things had been back probed way to many times and were not making good contact

 

[jap813]

that 2 cycle fuel line will collapse on itself and block vacuum from getting through and create a blockage when you NEED a small vacuum leak for it to run correctly, replace it with the proper type vacuum line

 

[Ecomike]

That's interesting. Should I go bigger and by how much?

I used a tappered universal male/male vac hose adapter that could be cut on either end to make the opening larger. It started at about .7mm and could be opened up (like cutting the opening of tube of caulk) to about 5/16". I settled with about 2 mm on mine IIRC.