For Renix 4.0L's, is there a warm-up idle that raises the idle a bit until the engine reaches operating temp? If so, how is it controlled? How many RPMs does it raise? What should the rpms be after fully warmed?

 

No. There is an idle "flare up" when started which settle down to base idle very quickly.

 

Thanks Mr. Cruiser!
Is that only for the Renix computers, or does the HO have this too? My 99 2.5L TJ has a warm up idle, so I was wondering if my '88 xj had the same thing, but I guess that is too much "technology" for the renix. (I'm not complaining, part of why I like the renix system.)

 

No.
OBD2 engines only have an open loop and closed loop. Open loop is maintained until the engine reaches normal operating temp (Approx.195 deg) and then the PCM switches to closed loop, this provides for a faster warm up.

 

simplicity.....

 

The reason I asked was because my idle (after the initial flare-up) settles down quickly to 750 rpm, but once it heats up (closed loop??) it drops down to 500rpm. So I thought there may have been a warm up idle, and the overall idle could just be adjusted higher.
But I see that is not the case, so I'm guessing something else is wrong here.

Now why would a hot engine want to idle lower? Something must be telling the ecu to idle lower once it gets to a certain temperature? Coolant temperature sensor?
Does the Renix ECU have preset fuel trims data that runs when cold, then reads from other sensors once at operating temp? Something is telling the ecu to change things when it gets hot...

 

I've seen Renix frequently go into closed loop in under a minute.

Now, what have you done to address this, if anything yet?

 

Throttle/Idle Stuff:
- Throttle body cleaned
- Stop screw adjusted
- New TB gasket
- TPS adjusted
- Distributor indexed
- New IAC (by standard motor products)
- New MAP (by carquest BWD)
- New O2 Sensor (by NTK)

Other recent things:
- plugs, rotor, cap, wires
- new cat converter
- new 100 A alternator
- kelly's cable mains (incl. ground strap replace, body ground, alt ground)
- dipstick ground, fuel pump ground


Idles fine when cold.

 

I also did these two tests and ran to operating temp:
- unplugged CTS, no fix
- unplugged O2 sensor, no fix

I thought that might rule those two sensors out since the ecu would not be getting their input and would have to rely on default trims.
(sorry if this seems dumb, but I thought it might prove something)

 

Are you getting 12+ volts to the orange wire on the O2 sensor when running?

 

So is 500 rpms to low at idle?

 

Are you going by the tach in the instrument cluster or another source?

TPS adjusted on the Engine side, right?

 

Yes, should be 750 rpm at idle.

 

Not sure about that, I'll have to check that out. So run engine and back-probe connector, or can I unplug?

 

Reading rpms from stock instrument cluster tach in the cluster.

Manual transmission here, and the TPS was adjusted at the throttle body, is that right? Key ON, adjusted to 0.83 V, reads smooth throughout range, at WOT it's around 4.67 V.