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whats is proper idle for a 4.0

M

mitsumotors

NAXJA Forum User
Location
Winnipeg
My 91' xj idles at about 700rpm. this seems a little high to me. does anyone know where exactly it is supposed to be idling and if there is any way for me to adjust it? thanks
 
mine idles at about 1500 rpm's.......
 
2000 4.0 - idles about 650-700RPM.
 
the only reason i feel that it may be high is because when i put my foot on the brake and put it in gear it pulls forward and the brake holds it but it really wants to go. and the brakes are all new everything.
 
My '94 700 RPM; '96 750 RPM. That is within specs acording to the FSM. Check your rear brakes for proper operration. They may not be holding properly. That would account for the lounging when you put the XJ ingear.
 
my 89 idles at 400-500 needs a tune-up and has a cracked manifold, but it dont hesitate.

i have a broken Blow-by, and a few other leaks to address, then i'll see where its at after that.
 
mitsumotors said:
check my brakes how? what am i looking for?
Click to expand...

When I first noticed something was wrong with mine was pure accident.

I ahd the rear axle on jack stands trying to find the source of my drive line vibrations. My foot on the brakes just the normal pressure on one would use when shifting from park into gear AW4 in "D" and the engine at idle. A kid said to me one wheel is turning fas and the other slow. :huh: WTF!! I have my foot on the brakes. None of the wheels should be turning :doh: To get to the point, one wheel had an oil leak and the shoes were soaked in oil. The other wheel had both pistons in the wheel cylinder siezed.

My solution wass to fix the oil leak along with two sets of brake shoes, two wheel cylinder and a replacement combination valve.
 
For 87-90 models you might also check the transmission side of the TPS at idle to see if it is off spec as it might be telling the transmission to get after it if it is out of spec.

750 at idle in park, and 550 at idle in drive, and 750 at idle in drive with the AC running is what I have.
 
I can't see how the TPS would affect this, as its just telling the tranny what gear to be in. Aside from checking your brakes as suggested above, I would check that the throttlebody->tranny cable is properly adjusted.
 
lawsoncl said:
I can't see how the TPS would affect this, as its just telling the tranny what gear to be in. Aside from checking your brakes as suggested above, I would check that the throttlebody->tranny cable is properly adjusted.
Click to expand...
The TPS on renix models have a lot to do with idle speed. The TPS (on an auto trans) has two sides, the engine side and trans side, and if you've ever had a renix you know all about idle problems and TPS adjustment!
 
lawsoncl said:
I can't see how the TPS would affect this, as its just telling the tranny what gear to be in. Aside from checking your brakes as suggested above, I would check that the throttlebody->tranny cable is properly adjusted.
Click to expand...

You may be right, and that is what I thought for 2 years while I looked for transmission / power problems in my 87 that finally turned out to be a TPS that was good on the ECU side (where I was doing the testing) and bad on the TCU side. Mine was telling the TCU to up shift at 1200 rpm and at 1,400 rpm at WOT. It would never down shift except during braking.

If the TPS is worn on the TCU side and the signal is jumping around who knows how it will act. I don't know for sure, perhaps it is poping in and out of gear?

But on second thought, after rereading the 1st post, I see his is not even a Renix, it is a 91, so it can not be Renix TPS issue.

So to answer his original question, no the 91 TPS is not adjustable.


mitsumotors,


What is your idle speed in park??????

If it is about 750 rpm, then yes, look at the brakes, or look for internal hydraulic transmissions problems.
 
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