1990 4.0 laredo

Let me begin with an apology for a long post and a small bit ofn history...Ok this is my first XJ and 4.0, It was my old mans since new, and having been a lifelong YJ, all 2.5 swapped for small blocks, owner (I just gave my owned since new '92 to my 18 year old & '93 to my 16 yr old, I'll have to get an '05 for my 5 yr old one day! lol) Anyway, I am bewildered by the differences between the 2 models...

I am having several issues all at once it seems, some I've seen many posts on and youll see my meaning. I got this car upon my return from the "sandbox" and it sat about a year to 2 years....

1- High idle. I have had different issues with this since driving it. It starts after several cranks, pump is good low pressure after sitting, so figure drain back and have ordered a check valve to splice in (strong gas smell often too not sure what thats about as no leaks can be seen and new gas cap)After start she goes up to 3k, settles down between 5-800 ish when cold. If I put in gear (R) and give it gas right away she dies, but if I just let it roll til I need to put in D, Im ok. after warming up, in park or nuetral, it sits at about 1500 and I get an occasional misfire or "bump" up or down in idle, kinda mellow rough idle. I have repalced the throttle body off another renix that I pimped from a job I worked at after thourough clean-up and testing of IAC and TPS of newer TB. I used a gasket compound as I was unable to get at TB gasket inside of a week where I was. prior to replacing it was always idling at 3k and only resolution was get out, pull a vac hose, restart then would idle @ 800 and reattach the hose and it would stay there. now its better but still "thumps" into gear. No discernible vac leaks, loose intake bolts or cracks in manifold or anything. New "E3 plugs, cap & rotor. & a relatively recent ECU installed. Any ideas out there?

2- Bad leaf springs. WTF? I know that springs go bad, but negative arch? I know they were replaced at maybe 150k and I'm at 210k. I picked up a pair off a '91 (flat) at JY for $20 and a short AAL for $25 from Amazon plus new shocks, u-bolts, and spring bushings. Should I just build this pack & swap or leave long spring in and build that up with the JY pack and AAL? I cant afford new springs and its my DD not lookin for a lift if I get @ inches I don't care but not my goal, I have a lifted toy already...oh and it bottoms out if I have any passengers other than my kid in car and the ride is ROUGH and Im used to rough rides but this is horrific!

3- I get a "moaning/groaning" sound in front end, sounds like bogging almost, if I hit a bump over 5mph while going straight or turning that goes away if I let off gas for a second as soon as I hear it. Also a "thumping" sound under DS floor if I hit a bump turning too. Ive replaced the front axle u-joints, rotors, everything is greased up and fluids are full. I see no apparent issues while under car and turning wheels, etc....

That's more than enough for today, its Friday! Anyway, I leave for the Gulf again in a couple months and I'd like to be able to feel safe leaving this with my ex wife so she can get my boy to & from school while I'm away. I don't have a lot of cash to throw at her as I'm not really working other than plumbing side jobs and SSGT pay grade = broke! I'm looking to get some ideas, and a game plan together to make her safe for 56 daily miles of Chicago driving for the winter.

1990 4.0, 4spd auto, 242 TC. Any questions feel free to ask me on yahoo mail: chicagomarine0291 is my addy!

Thanks in advance for any help!!!

Well, first off, welcome to the forum. It sounds like you well know your way around the Jeep thing. Suffice to say that the XJ is quite a bit different than a TJ, YJ etal.
All I know about Jeeps is from this and other limited forums and my own experience with only RENIX 4.0 XJ's and MJ's.

1.) One thing I do know about the RENIX is that it's good old fashioned mechanics (except for the mix of metric and SAE and the bedeviling torx bolts). With the 4.0 and driveability issues it usually boils down to vacuum and electrics. After you chase down one gremlin, another pops up. BUT I wouldn't swap my 90 for an HO ever.
Someone will chime in with your idle problem. Since it abates when you change the vac pattern I'd suspect the EGR function.

As far clunking into geaqr, does it happen when the idle is running >1K or just as you're traveling, like from gear to gear. joe_?

2.) XJ's are known for their flat springs. When my leafs were sagging I looked around town (you can' spit around here with out hitting an XJ) and checked out their leafs. Every one I looked at had flat springs. I looked at budget lifts and AAL's but eventually opted for new packs and haven't had a problem since, with only 3" lift I didn't really have to change anything else except shocks. Building a pack is very easy with JY parts too.

3.) I had a moaning/whailing sound in my front end that turned out to be the A/C compressor OR the harmonic balancer. I should have driven the Jeep between these jobs but <doh> I didn't. The moaning is gone.

As far as the thump/clunk I'd first look at the condition of the control arm bushings, upper and lower. Then I'd look at the front shaft u-joints. If you have the double cardan style I think there are 3 joints. Removing the front shaft and going for a spin will give you a better idea.

It's my Friday too. Cocktail time!!

The High idle when starting problem is probably the intake gasket. The exhaust manifold gasket and the intake gasket are one piece. The gasket swells and seals when it warms up. Thats why is smooths out. Its either that or the idle air control (iac) sensor. The grinding and clunking sound is the unibearing hub assembly on the driver side.
As for the leaf springs it is really cheap just to get them re-arched. prolly need some new shocks to.

Semper Fi, Mac.

Ok, here is a link to the RenX high idle thread--over ten pages on the issue: http://www.naxja.org/forum/showthread.php?t=905849

I agree that a intake leak high idle can present when cold, then as the engine and manifolds warm up and close the gap reduce the idle. However, as you have some success when effecting the vacuum system I'm going to lay a cookie or two down on an EGR problem.

TEST your EGR system, info from 90 FSM:

Warm the engine to normal operating temperature.

Operate engine at idle speed.

Check vacuum at solenoid vacuum source.

Disconnect the hose and attach a vacuum gauge to it.

Vacuum should be at 17 inches.

If vacuum is low, check the line for kinks, twists, or a loose connection at vacuum connector on intake manifold.

If vacuum is ok, remove gauge , reconnect the line and proceed to next step.

Check vacuum at solenoid output port.

Disconnect the line and attach a vacuum gauge to output port. Vacuum reading should be 0 at this side of solenoid.

If vacuum reading is 0, leave the gauge connected and proceed to the next step. However, if vacuum is present check solenoid/ECU operation with the DRB-ii tester.

Disconnect electrical connector at solenoid and note vacuum at output port. Vacuum should now be present at output port.

If vacuum is present, proceed to EGR valve test. However, if vacuum is not present, replace the solenoid. Test the EGR valve as follows:

Leave solenoid electrical connector disconnected. Note engine idle.

The engine should idle roughly or stall. If this occurs the valve is ok. If the idle does not change, proceed to next step.

Disconnect hose from the EGR valve and connect a hand vacuum pump to EGR nipple.

Apply a minimum of 12" of vacuum to the valve and note engine idle. If engine now idles rough inspect the vacuum line between the EGR valve and the solenoid.

If the idle did not change, remove the EGR valve and inspect the valve and the exhaust passage in the manifold for blockage, repair as necessary. If no blockage is present replace the EGR valve.

TRANSDUCER VALVE:

Disconnect the transducer vacuum lines and the back-pressure line (bottom). Remove the transducer. Plug the transducer output port. Apply 1-2 pounds air pressure to the back-pressure port. Apply a minimum of 12 inches of vacuum to the input port. Replace the transducer if it will not hold vacuum.

Your "goal" idle is 700-750 RPMs (use an external tach), when in DRIVE, service brakes applied and AFTER 20 minutes of driving, when the engine and transmission are both fully warmed up.

There is a 3/32 allen screw that effects the throttle plate--IT IS NOT, REPEAT NOT, AN IDLE ADJUSTMENT SCREW. That poor little abused screw's only purpose in life is to keep the mean and nasty steel throttle plate from slamming fully closed and damaging the alloy throttle body. Pull the intake tube. Back off the 3/32 screw until the throttle plate is fully closed and the screw is not effecting the throttle plate position at all. Now, slowly turn that screw back in until you can see the first perceptible movement of the throttle plate--STOP. You are done. Put the intake tube back on and now adjust the TPS to specs. The IAC will handle the idle speed just fine once the other gremlins are taken care of.

Build yourself a bastard pack. Some info: http://www.naxja.org/forum/showthread.php?t=1004504

Without an arch you have no "spring", so rough ride time. From your description I would grab a late model set of springs from an XJ, maybe just run those like they are or grind off the "eyes" from your old pack and add just that one leaf to both sides.

Good luck.

i was out in the boonies this morning and noticed the jeep started to feel like it was pushing down the road and the breaks were fading fast...put it in park and the idle was hovering around 2 grand. limped it back 20 miles to the main road before i shut her down and found this under the hood..



broke the line to the map sensor...little tape and she started back up and made it home (brakes and all).

May want to give this line a quick check.

Thanks for all the ideas fellas. I will post as I get to this and see what we have. Its been a hellish week!