90 XJ high idle HELP!

[Wild Bill 53]

My 90 XJ is being a bleepin' jeep and I can't figger' out why. Started out with a low idle and stall in traffic after warm up. Started with a tune up (nightmare with broken distributor ear), cleaned throttle body, new Idle Air Control valve, new throttle position sensor (have no idea how to "set" it), front and rear vacuum harnesses, MAP sensor and the truck now idles at (I'm guessing) over 850 rpm! I am disappointed in my attempts to get this jewel running right and the problems just keep compounding. Started it today after a "break" to regroup my mind and the heater hose has started leaking! Please, can someone help with the high idle issue before I feel like this: Hasta

 

[TRAILREADYXJ]

Givin the symptoms you posted it sounds like the TPS is out of adjustment, or defective (not too uncommon for parts store brands to be faulty or out of spec when new). I can't remember the method for testing, I know you need a multimeter and need to test for and adjust for proper voltages...I'm sure the info is here or on google if you do a little searching. Good luck!

 

[Catch22]

vaccum leak?

 

[TRAILREADYXJ]

vaccum leak?

This could be possible as well for the high idle, but doesn't explain the low idle/stall when hot. Definitely check all lines, as well as the one to the MAP sensor.

I'm still leaning toward TPS though, I had that issue in almost every Renix XJ/MJ I've owned, and usually it could be repaired by adjusting it.

Also be sure to check your sensor grounds on the passenger side of the head, this is a major problem area and can cause all kinds of issues! Don't just check to see if they're tight, remove and clean the terminals to ensure a proper ground.

 

[Catch22]

This could be possible as well for the high idle, but doesn't explain the low idle/stall when hot. Definitely check all lines, as well as the one to the MAP sensor.

With the large amount of vac lines in the pre 91s I can see it a vac line snapping easy. It could also be multiple issues like a vac line and a bad upstream o2.

 

[SafariJeep]

If you did not not do the TPS adjustment that is almost certainly your problem. Here is the procedure:

http://billyxj.tripod.com/SENSORS1/page1.html

TPS - 1987-1990

The 1987-90 sensor has two pigtail leads. One has an in-line 3 pin
connector, containing 3 wires. The other has a square four pin
connector with 3 wires. The square connector is the one that is used
for the transmission controller. These wires can be identified by the
letters which are stamped into the connector.

Adjustment is simple though backward by most TP standards. With the
harness connected, test the voltage on pins A, B & D. The voltage on
pin A (reference voltage) should be approx. 5v

Voltage on pin D (ground) should be less than 0.1v. If the voltage is
higher, an additional ground wire can be spliced into the circuit.

Pin B is the TPS signal to the controller. The voltage on pin B should
be 4.0 - 4.4v at closed throttle. At full throttle, the voltage should
be 0.2-0.5v. The TP sensor has elongated holes for the hold-down screws which allow it to be ajusted.

Adjustment is as follows: (comments in brackets are mine)

1. Turn the ignition switch to the "ON" position

2. There are 2 wire harness connectors attached to the TPS. Inout/output voltage is checked at the SQUARE, FOUR TERMINAL CONNECTOR (though it only actually has 3 pins). The terminals are identified by the letters A,B,C,D molded into the connector.

3. Do not unplug the connector. The voltmeter leads must be inserted through the back of the connector to make contact with the terminals. Connect the positive lead to terminal A and the negative lead to terminal D.

4. With the throttle plate in the closed position, note the "input" voltage. It should be approx 5.0 volts

5) Remove the voltmeter positive lead from terminal A and connect it to terminal B. The "output" voltage should be 4.2 volts - 82% of input voltage. (NOTE: on my XJ, the input voltage was only 4.6 volts so I had to adjust the closed throttle output voltage to 3.8 volts as this is 82% of 4.6)
If this is not the case, continue with this procedure

6. Adjust output voltage as follows: with the voltmeter leads still attached to, carefully loosen the sensor mounting screws and slowly rotate the sensor until the output reading is 4.2 volts with the throttle closed (or 82% of your input voltage). Then, toghten the sensor mounting screws securely.