I have done most of the testing for bad sensors to find a fast idle situation. I cleaned the throttle body and then started testing sensors since I still have the fast idle problem. The dash is apart right now, AC issue, and I would like to test the ECU but I can't find the thread that has the wires to check. Any help will be appreciated.

I'm in the Rio Grande Valley, does anyone know a good XJ mechanic down here? I would like to get some things fixed but don't want to pay for someones training.

 

Vac leaks will cause a fast idle unless the idle stepper is stuck open. The 4.0L has a pretty common issue with intake gaskets leaking also any hoses that maybe disconnected or rotted will be a problem.
You can look for leaks using brake clean on suspected areas with the engine running. You don't have to spray a lot, just a little and the engine will surge or die when you hit the spot.
Most common area I've seen is intake to head.

 

go to www.cruiser54.com and do Tips 1,3,4, and 5 before doing anything else.

 

also check the vac ball accumulator that you will find behind the front bumper. common for a vac line to slip off. or maybe your vac ball is cracked.

another thing you can do at home is to go out and buy yourself a nice cuban cigar, glass of scotch is optional, and blow some smoke into the vac line and have someone see where the smoke comes out. that should indicate where the leak is.

i say use a good cuban, because smoking a cheap cigar is gross, and also, a good, (real) cuban gives off a nice thick smoke that will help fill the vac line.

it's cheaper than a shop using a smoke machine, and you get to enjoy a nice cigar.

 

Odd thing about the Renix system is that most times with a vacuum leak it idles DOWN, not up like the 91 and later systems.

 

Yep did 1 - 5 thanks for your service Cruiser54.

I'm ready to buy some parts or have someone else do the work. What is that thing on the side of the throttle body closer to the head? Is that a good thing to throw money at? I may have damaged it when taking it apart.

I forgot, what is the check for connection to the ECU? I would like to get the dash back together.

 

The TPS?
That's what I was gonna suggest after those Tips were done. It's sensitive. In my Tips is the proper adjustment procedure.

 

Note from DJ
If you are referring to the thing with the red arrow pointing to it; that is the Idle Steeper Motor.
If you are referring to the thing with the green arrow pointing to it; that is the Throttle Position Sensor

 

The idle stepper motor is the winner.
OReilly price
BWD Idle Air Control Valve/Motor
Part #: 21771 Line: BWD
Part Fits 1990 Cherokee
$64.99 Each

 

What were the results of Tip 5?

 

Cruiser it was less than 1 ohm. I think it was 0.2 ohm but it's been a while. I am an electronics technician by trade and training so I know my way around a VOM.

When I pulled the Idle Air Control Valve/Motor from the throttle body I think I pulled the plunger out or some other stupid thing I wasn't supposed to do, thats why I'm thinking of replacing that first.

 

Gotcha.

It's constant high idle then?

TPS can be intermittent.

 

When the engine starts it runs about 500 RPM then after a few seconds it jumps up to 1500 or so. The warm up time is less than 30 seconds for the idle to jump high.

 

Consistent or intermittent?

 

Intake bolts loose ?
Morning Major.