Day 2. The adventure begins (Not a FUN adventure)

So I drove my new to me 88 cherokee around town on some errands today. I can already see where paychecks will be headed.

I fired it up at the grocery store and it rev'd to about 2500 and just sat there. I drove it down to the parts store (I thought it needed a battery) and when I pulled up and put it in park it rev'd up to nearly 4000 and I cut it off. Pulled the battery and went inside and they tested it and said it was good. OK... Put the battery back in and they tested the alternator.. also good.

With a charged battery and a good alternator it was still a little sluggish when I started it, it idled at just under 1000, and drove home perfect. Now I am scared.
What else could draining the battery? or make it sound like it has a dead battery when trying to start it? Weak starter?
What would cause the motor to rev up so high? Ignition parts? I checked the throttle cable and it wasnt stuck.

WHAT THE HELL DID I GET MYSELF INTO!?!?!?!

Also it has the 4.0 I6 and auto tranny that I believe came off of a later model.

Ok, just went and tinkered a little more.

The oil pressure at idle is between 25 and 30. It goes a little over 40 while driving. Is this a big problem?
Found an oil leak at the rear main seal. Im currently searching for instructions in the forums, but is this something I could do with basic mechanical knowledge and basic hand tools?
Thats what I have found so far. I have wanted an XJ for a while now so I'm kind of excited to work on it. Too bad I have no cash now.

Ok. Calm down, take a breath, and start over with your explanation.

Not sure how your battery would effect the idle. The Renix 87-90 XJs have an ECU that is strictly real-time processing--no memory to be screwed up by poor power. However, like any electronic engine management system, if the voltage drops below 9 volts things will go wonky.

So, you have a slow cranking issue? Describe it.

Now, how to get a 2500 or 4000 rpm idle--sounds like a large intake leak. I'm posting a link to the Renix high idle thread, read through it, follow some of the suggestions. If something doesn't make sense to you, post up and we can discuss it.

Link: http://www.naxja.org/forum/showthread.php?t=905849

Good luck.

Ok- to clarify what I said before--

I thought the battery was going out because thats what it sounded like when I was starting it, like it wasnt getting enough juice. Now that I know the battery is charged and good, and the alternator is good, it still sounds like the battery is weak.
I was thinking the ground may be bad? Im going to get some new battery cables tomorrow because it cant hurt anyway.

I am going to start reading through the high revving thread and will post up any questions I have.

Thanks for the reply

Ok. Cables or starter-solenoid may be at fault for slow cranking. Upgrading to heavier main cables is a pretty good idea. You can check for voltage drop across the cables. Here is an article on measuring: http://www.aa1car.com/library/voltage_drop_testing.htm

Grounds are critical on the Renix era--87 to 90--XJs. There is ONE single unibody ground, as self-destructing braided strap from the rear of the head, driver's side, to the firewall. Replace it with a 4 or 2 gauge cable. The grounds at the dipstick tube are for the ICM--ignition control module; the ECU--engine control unit; and the o2 sensor, and a couple other things. You need to strip all grounds down to bare metal, treat with an anti-corrosion agent, and make them TIGHT.

Common oil leaks:

Valve cover gasket, oil runs down to the bottom of the engine and can mimic a RMS seal leak.
RMS
OFA o-rings
Distributor gasket
Oil pressure gauge sending unit and/or its adapter
Pan gasket

Best to clean things up and look for the source of your leaks. Use Simple Green 50/50 with water in a garden sprayer, wait at least 15 minutes then hose off--WARNING: always be careful around the throttle body, the TPS can be ruined VERY quickly by water.

Your oil pressure is Ok. That said, hooking up a mechanical oil pressure gauge to check it is always good for a little piece of mind. FSM minimum pressure at idle is 13 psi; rule of thumb is 10 psi at idle, 10 psi per 1000 rpm.

Also, make sure you service the CCV--crank case ventilation--system or you will end up with oil in your air filter. Do an advance search for Cruiser54 posts, he has posted up instructions for modding the valve cover to reduce problems for the Renix.

Not sure about the weak start, but as far as the idle something cheap to check could be the coolant temp sensor. Mine went out last week on my 98xj and it never threw a code. It started reving up and idling bad and I even smelled gas at one point where it smelled like it was "flooding" out. The only symptom I had was the temp gauge would bounce around. Replaced it for $20 bucks at Napa.

Speaking of the TPS, the majority of Renix high idle situations come from a failed or mis-adjusted TPS. Read here: http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm and scroll down to TPS adjustment. Make sure to check for a smooth voltage sweep as the arm is moved like the article mentions.

Thanks for all the info guys. Hopefully I can figure this problem out..

I tightened the intake and exhaust manifold bolts after reading through some stuff here but the High Revving Idle problem came back today after I got home. If a vacuum leak can cause the problem then it will take some time to find all the connections and probably replace some hoses. I am going to replace the battery and ground cables also and see what happens.

JJacobs - I checked out the article and it said to adjust the new TPS. How do you adjust the sensor? I probably read it wrong.

Joe-- A previous owner made a mess of the wiring so I will have to really clean that up before I can spray anything under the hood. There are loose and broke connections all over the place.

I appreciate the help. I am stoked to have a Cherokee FINALLY! I dont mind working on stuff I enjoy, so I will definitely be coming back with questions.

Concentrate on the EGR--when they are fouled up they will sometimes give you a normal idle until the stick open again.

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.