• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Renix ECU help

M

mpro1

NAXJA Forum User
Location
NY NY
I have a slight issue that i could use some input on........My 1990 4.0 manual cherokee has an strange idle cond. .....I have searched and read many high idle threads....i have obtained a pdf copy of the test procedures for the renix system.....the 4.0 after initial warm -up will idle correctly......when fully warm it will idle correctly.... after giving a little gas in neutral lets say above 1500rpm the idle will not go below 1200rpm....if i then engage the clutch a little to bring the rpm's down below 1000 it will idle normal.....so i have checked and corrected vaacum leaks.....have also completly cleaned carbon from the tb and aic stepper motor......i have correct voltage input of 4.98V and output of .8v set on the tps...i also tested the output resistance range according to renix service manual on the tps all checked out ok....the ground also checks out...Here's the strange thing, being that when i unplug the tps during the slightly high idle cond. the engine rpm returns to normal....That makes me believe the sensor is bad ...but tests indicate that is good...if the tps is not bad....What would cause this???? and Why does the problem correct itself with the tps disconnected if the tps tests good??? .........I don't like wasting money on changing out good sensors......Can someone steer me in the right direction???

Thanks ..........................Matt
 
Put a drop of oil behind the piston on the IAC. Just let a drop or two of thin oil run behind the piston. Clean the IAC connector, something I've noticed is the IAC often acts up when the battery is low and/or when it doesn't get enough juice.
Clean the connector on the TPS plug and clean the (ECU) grounds well by the dipstick holder. Check the ground ring (at the dipstick holder) for corrosion at the crimp, some are soldered some aren't.
I've heard people say this doesn't actually do anything (with the Renix), but my experiences have been different. Disconnect the battery for awhile, then take it for a test drive.
I had one 87, that would idle high, because the intake would get hot and flex a little causing a vacuum leak. You can try retorquing the intake bolts, but be carefull of the studs, they often snap off easy. The intake bolts lossening up is pretty common.
1200 RPM when hot, sounds like the IAC or a small vacuum leak.
I often disconnect my AC compressor when driving off road and turn on the AC at the HVAC controls. It will idle up to 1200 and the aux fan will come on.
 
Still have not fixed this problem..... what else to check EGR, Mat, o2 map ???

Replaced Intake gasket a couple of years ago... Mabe retorque the bolts??
 
I have removed grounds cleaned them and reinstalled with di-electric grease..... also the tps settings are correct and i get a smooth steady volt increase as i open and close the throttle body......

when cold it seems to idle normal...... after driving for a while it creeps up....

when i drive above say 1500 or greater rpm.... and dis-engage the clutch (throw it in neutral) (stick shift) the idle will remain above normal around 1000-1200 until i engage the clutch and use it to bring it below 1000 then will settle around 750 rpm.... Strange uh.....

Thanks for the reply .....................Matt
 
mpro1 said:
I have removed grounds cleaned them and reinstalled with di-electric grease...
Click to expand...
Should be okay as long as there's good metal to metal contact. Dielectric grease is nonconductive.
 
mpro1 said:
I have a slight issue that i could use some input on........My 1990 4.0 manual cherokee has an strange idle cond. .....I have searched and read many high idle threads....i have obtained a pdf copy of the test procedures for the renix system.....the 4.0 after initial warm -up will idle correctly......when fully warm it will idle correctly.... after giving a little gas in neutral lets say above 1500rpm the idle will not go below 1200rpm....if i then engage the clutch a little to bring the rpm's down below 1000 it will idle normal.....so i have checked and corrected vaacum leaks.....have also completly cleaned carbon from the tb and aic stepper motor......i have correct voltage input of 4.98V and output of .8v set on the tps...i also tested the output resistance range according to renix service manual on the tps all checked out ok....the ground also checks out...Here's the strange thing, being that when i unplug the tps during the slightly high idle cond. the engine rpm returns to normal....That makes me believe the sensor is bad ...but tests indicate that is good...if the tps is not bad....What would cause this???? and Why does the problem correct itself with the tps disconnected if the tps tests good??? .........I don't like wasting money on changing out good sensors......Can someone steer me in the right direction???

Thanks ..........................Matt
Click to expand...
I have done extensive work on this same problem for 2 years on the same jeep. Mine is fixed now!!

My first choice would be that there is still at least one poor or intermittent ground. There are two on the firewall and two on the engine block. The most important one is the one next to the oil dip stick tube, it grounds the sensors and electronics like the TPS and it runs to the battery and the firewall. All three must show less than 1 ohm of resistance from point to point. There is one more ground from the passenger side engine head, top rear, and the firewall.

Remember, less than 1 ohm is what you want. I had 8 ohms on one of mine and it made mine idle high, even with all new, perfect parts.....

If all the grounds are perfect, than I would look for a small vac leak that shows up as the engine heats up. Small vac leaks can come from anywhere, including the valve cover connections and gasket, all the little and large (some hiden behind the firewall) plastic vacuum lines, intake manifold (bottm side which is so well hidden)....etc.
 
Check the IAT sensor on the intake behind the throttle body. You can check it with an ohmmeter.

Have you checked the vacuum with a meter?
 
old_man said:
Check the IAT sensor on the intake behind the throttle body. You can check it with an ohmmeter.

Have you checked the vacuum with a meter?
Click to expand...


I have checked the vacuum with vac gauge... have changed 95% of the vac lines and inpected the rest.....All good....still i have not found any vac leaks.... I will check IAT Next Thanks.......
 
IAC (idle air control - stepper motor) might be dragging inside port when things are hot. Like all Renix owners I struggle with this too and when I get frustrated - unplug the IAC once it's idling HOT and good with AC on, if equipped. This will leave IAC parked in position for HOT idle. When cold, you'll have to keep it running with throttle but once warmed-up it will idle fine and never hang-up again!
 
mpro1 said:
I have removed grounds cleaned them and reinstalled with di-electric grease..... also the tps settings are correct and i get a smooth steady volt increase as i open and close the throttle body......

when cold it seems to idle normal...... after driving for a while it creeps up....

when i drive above say 1500 or greater rpm.... and dis-engage the clutch (throw it in neutral) (stick shift) the idle will remain above normal around 1000-1200 until i engage the clutch and use it to bring it below 1000 then will settle around 750 rpm.... Strange uh.....

Thanks for the reply .....................Matt
Click to expand...

not strange, my 89 idles exactly like yours until i do the little clutch trick that you do. its been doing this for years and ive done everything that has been mentioned. i have 2 grounds from the engine to the firewall and it still does this sometimes. exhaust manifold was loose and missing bolts, fixed that and it didnt help. tps calibration, still does it.......................

ive come to the conclusion of just living with it. hard to do at times because for some reason,we, or maybe its just me, go crazy when it doesnt idle perfect. for me, it no big deal anymore and if i want to drop the rpms, i pull out the clutch.
 
You must log in or register to reply here.

Similar threads

I
High idle, smells like gas, running out of things to replace
Replies
2
Views
2K
Inverhyt
I
C
'98 XJ p0123 help, TPS high voltage
Replies
18
Views
3K
Tim_MN
Tim_MN
Z
1990 renix electrical issues
Replies
3
Views
85
cruiser54
C
9
Renix lowish idle
Replies
10
Views
1K
90xj06
9
A
Renix TPS nightmare
Replies
19
Views
3K
Saudade
Saudade
Back
Top