STUMPED> 1990 XJ

[XJ89JEEP]

I"m having issues with my 1990 XJ its 100% stock with 138k Larado package and a renix 4.0 auto-

The problem I'm having is that about every 3-4 times i start it, it turns over for a while then(it always ends up starting) it will rev to 3000 rpm and the immediately drops to 0rpm if you don't help it out by stepping on the gas to make it run. This happens when its either cold or hot. Most of the time it starts with no issue but it idles at 500 rpm (seems low to me). When it is running it runs great, no hick-ups or anything. I've had the jeep at the shop for over two weeks and the mechanic thought it was the EGR valve, so he blocked it off and it helped for about a week.(still currently blocked off) Then back to the usual problems. Also power seats and power locks don't work, and none of the dash lights work.

I HAVE REPLACE THE FOLLOWING PARTS...
plugs
cap
wires
rotor
temp sensor(on the block)
MAP sensor
TPS sensor
CSPS crank shart position sensor
EGR sensor
O2 sensor

I think that's it. all parts i replace with NEW not used parts.
I also pulled all the carpet and seats, thinking there was some corroded wires but not even a drop of moister, i also looked under the dash to see if i could spot something visually, nothing. I've check all of the fuses and they are all good.
The jeep has never been in any type of accident or anything. I've invested so much and still nothing, i have read forum after forum, post after post. I've done everything and tired that i could find online. any body have any more ideas that could help me out?

THANKS GUYS

 

[joe_peters]

The idle, following 20 minutes of driving, should be 700-750 RPMs, transmission in DRIVE--parking brake applied and someone's foot upon the service brake pedal. Don't rely on the IP tach, hook up a separate one.

In my experience the occasional symptoms you are experiencing are related to the EGR system, often times the vacuum transducer valve. How to test the EGR system:

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.

In fact, this whole thread may be of interest to you: http://www.naxja.org/forum/showthread.php?t=1040508

Also, the ECU energizes the B Latch relay for 3-5 seconds after the ignition has been turned off to allow the IAC stepper motor to move to its pre-programmed position for the next start up. This is done because the Renix ECU is strictly real-time only and has no memory.

Good luck.