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Old 01-27-2013, 01:07 AM   #1
DOCTORBILL
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Need Some Advice on Jeeps

I have some questions -

1. My '89 Jeep Comanche 4x4 Truck idles at 1,000 rpm. What is normal ?
Is the idle controlled by the computer or that screw on the throttle block ?
I have messed with the screw, but the idle stays at 1,000 rpm !
Straight six - wouldn't EVER have anything else !

2. Are all Jeep Floor Stick Shifts hard to get into second gear when cold ?
Had a '95 Cherokee with a floor 5 speed stick and it did the same thing......
When good and warm, shifts into 2nd nicely.

3. My '89 Jeep Comanche 4x4 Truck gets 16 mpg - used 4x4 a lot.
What is normal. My '95 Cherokee got 22 mpg - straight six.

4. Where the Heck is everybody - hardly any replies on this forum.....

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Old 01-28-2013, 11:23 AM   #2
denisond3
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Re: Need Some Advice on Jeeps

The original idle spec for the 'Six' was probably more like 850 to 800. The small screw could open or close the throttle plate a little, but the computer is going to try and control the idle speed to the original rpm - until the throttle plate is opened far enough that even with the Idle Air Control Valve all the way shut the engine is still turning faster than the computer prefers. (If you unscrew that adjustment till the throttle plate is entirely shut - it would probably run fine once started and running, because the IACV would be opened a little more by the computer at idle. However I think the throttle plate has to be slightly open for better starting from deep cold. Thats my guess anyway).
I would think its more likely that you tachometer is 'off' a little due to aging rather than that the computer is running it at 1000 rpm on purpose.

When its cold you can expect some resistance going into 2nd, because of the effect of stiff oil, and snychros that arent as effective as new. Lots of folks use a heavier trans fluid that the original stuff. I know guys using 80W trans fluid in manual transmissions designed for Mercon III auto trans fluid - and they have very noticeable stiffness until the trans warms up.

I kind of thought 16 mpg was considered common for the 4.0 liter Cherokees, but that might be with the automatic transmissions. The expected mpg with a 4 by 4 pickup might be different (lower) based on the final drive ratio in the differentials.

I have an 86 comanche with the 2.5 liter four and the 5-speed transmission used at the time (a different 5 speed was used from 87 onward). I get 25 mpg on the open road. Mine has no options; no power steering, no a.c. no all wheel drive. I only wanted the 2.5L four cylinder engine.

Im looking to find an 86 - 92 Cherokee with the 2.5L engine, a 5-speed trans and all wheel drive, for use in the hilly parts of Central America. And I want it with a bad engine & clutch, so it will be cheap. Havn't found any yet though.

I think there are other Jeep forums with more activity.
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Old 01-28-2013, 11:36 AM   #3
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Re: Need Some Advice on Jeeps

Quote:
Originally Posted by DOCTORBILL View Post
I have some questions -

1. My '89 Jeep Comanche 4x4 Truck idles at 1,000 rpm. What is normal ?
Is the idle controlled by the computer or that screw on the throttle block ?
I have messed with the screw, but the idle stays at 1,000 rpm !
Straight six - wouldn't EVER have anything else !

2. Are all Jeep Floor Stick Shifts hard to get into second gear when cold ?
Had a '95 Cherokee with a floor 5 speed stick and it did the same thing......
When good and warm, shifts into 2nd nicely.

3. My '89 Jeep Comanche 4x4 Truck gets 16 mpg - used 4x4 a lot.
What is normal. My '95 Cherokee got 22 mpg - straight six.

4. Where the Heck is everybody - hardly any replies on this forum.....

DoctorBill

4: Well pardon ME for not being on here 24/7. 10 hours isn't a bad response time, considering how many internet forums there are online nowadays, AND to get an answer when your initial post was at 2am!!

3: I basically get 22 on the highway (under 65) and 18 on the highway (over 65). 16 is normal for around town, or using 4wd a lot so this sounds normal. If you want to check, get it warmed up then out on the highway, steady speed, for 1/2 hour and see what you get.

2: Not all Jeeps, but many transmissions do this. It could be a number of factors including wear. However I've found that a little moisture will cause that symptom also; try a drain / refill of the transmission and see if it doesn't help.

1: Mine idles at about 1000-1100 when first started, and 850-900 when warmed.
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Old 01-29-2013, 11:14 AM   #4
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Re: Need Some Advice on Jeeps

Thanks denisond3 -
I did a Google Search and wound up here:
http://www.jeepforum.com/forum/f53/

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Old 02-12-2013, 02:41 PM   #5
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Re: Need Some Advice on Jeeps

Hi i'm new on this forum I have problem with a 2002 jeep grand cherokee and at first po 304 codes which was b1 s2 O2 sensor I replace both and that bank but after I replace it the code po138 came up and as well p1294 and RPM start working wrong so I replace the iac valve and code po505 came up and since I rwplace that valve RPM been very unstable some days normal and now I little above normal about 1200 RPM
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