low idle

My 88' XJ has been a really low idle. At start up its at 800, after driving it around and sitting at a light it will idle at 400, almost wanting to stall. I just clean the throttle body, new gasket, idle air motor, throttle position sensor and map sensor are about a month old. It did stall out 2 times sitting on a hill at a light. Is this the fuel pump, I haven't ever replaced it and it is a worry for me if it goes out on the highway. Any help.

Hmmmm....


Seems like you've replaced all the other culprits, so looking to the fuel pump sounds like the right direction.

You might try the fuel filter and ballast resistor first, but if you're still on your original pump on an 88, it's probably a pretty good idea to replace it anyway. I bought mine for my '88 at Autozone, but I've heard bad things about them since then. You might look at the dealership or maybe do a little research because I specifically remember reading that some of them were better than others.

Also, there should be some write ups on the fuel pump replace on this site. But here's my quick advice:

Undo battery, of course.
Have less than a quarter tank of gas.
Jack up the back to give yourself some room.
Get a brass punch (to avoid spark when you're hitting the lock ring)
Definitely don't pull the tank, which I think Haynes says to do.Just cut all the plastic ties holding the wiring sending unit. That'll give the the room to twist the whole thing up sideways and pull everything out.
Clean off the electrical connectors, esp. the negative. They corrode a little and keep power from getting there. Happened to mine.

Ummm... wear goggles. Gas in the eye sucks.

Don't totally discount the map sensor, I had a brand new O2 sensor that was bad.

Thanks for the help, I'm going to replace the fuel pump this weekend. The tips were much needed thanks. The MAP and O2 were all replace last month with the new engine. This low idle problem started last week. So, the pump is next on the list.

If yours is a 4.0, there are two passages in the throttle body are used to regulate idle speed. I guess there are three if you count the throttle plate and its associated stop screw. Anyway, in addition to the idle air motor there is another port on top of the throttle body. If this became plugged it could explain your symptoms. It has an adjustment screw under a "tamperproof" cap. If you cap off the idle air motor's intake passage with your thumb, then the other port should be able to sustain the idle at about 400 rpm.

Juice,

There is a TSB out on this issue for our 88 XJs. Take your XJ to your dealer tell them the problem. They should clean the throttle body and the TSB has a procedure to modify the IAC solenoid.

I had this problem in January, the dealer mechanic solved the problem.

Martin

does the TSB cover '87's as well???

.

Martin,
What recall are you talking about?
This is the list I found.
http://www.alldata.com/TSB/04/880417CN.html

Thanks for the help. Juice

If you change the first two letters in the big long list of letters in that link to 87 it will show you an 87 with 4.0, and any other year that you change.