97 cherokee bad idle

the 4.0L runs rough at idle. i have changed the air filter, plugs, wires, rotor, cap and added injecter cleaner... also replaced the IAC motor and cleaned it all out. Any ideas? maybe the TPS MAP?? help...

Egr?

Adding most injector cleaners to your tank will do about zip.....especially if the injection system has been neglected and never been cleaned thoroughly. I would have the vehicle serviced with a professional injector and intake cleaning.... did this on my '00 and what a difference. This service will remove and clean out any deposits in the injectors and intake track. It shouldn't run more than $75 or so. Once you get the injectors clean, use Chevron Techron injector cleaner with every oil change... this stuff is expensive ($9 for a 20 gallon dosage) but it *does* work for minor cleaning and maintaining of the injectors.... with the other stuff you're just wasting your money.

mike

havn't had a chance to look at it any more, but i did notice the last time i drove it that it would stumble a little under 2000 rpms when i held it steady in park. so i am not sure what is up with it. any other ideas before i go blow alot of money to get it fixed?

could rough idleing and slight surges (150rpms of less) be caused by a fuel pump that is about to go out??

If it is missing and running ragged at a constant rpm, I would suspect dirty injectors. Get the injector cleaing done and see what happens.

You could have a bad EGR valve that's allowing too much exhaust gass to recycle back into the intake. Might be the valve pintle is worn or the diaphragm is stuck open a bit.

Shouldn't cost too much..... injector cleaning should run around $75-$100. The EGR valve might run $40 (a best guess on my part)

mike

For about 20 bucks you can get a digital multimeter to test the TPS and the MAP sensor. However, if one of these sensors was bad, you'd have a check engine light on.
Erratic fuel pressure would make it idle bad. Brace yourself, the fuel pumps are expensive. Even more so if a mechanic replaces it. If it is the fuel pump, it's going to solve the diagnostic problem for you soon by kicking the bucket at the most inconvenient time possible. Have the fuel pressure tested.
As for the EGR, I doubt your '97 has one. My '96 cherokee doesn't. My Haynes manual indicates EGR valves for model years up through '90 only.

One thing I would suggest is to pull each end of all the vacuum hoses and inspect them. Look for internal and external splits in the hose ends. Seeping vacuum leaks will cause bad idle problems.

thanks for the suggestions! i have already run injector cleaner through it with no change. i have noticed that lately it is running rougher and rougher. not sure about having an EGR, but will check it out. As far as checking the MAP and TPS, what should they read? and what is "good" fuel pressure in psi? i plan on doing all of this myself to save some money and i would like to fix it before it does break down in the worst possible circumstance! thanks again.

Suggestions...
CHange the cheap stuff first:
Fuel filter,depending on year it MAY be in the tank
fuel pressure regulator
check all vacumn lines...if they are hard plastic lines they can be spliced using 5/32 ID gasline hose,it withstands the heat in the engine compartment better
At night, with the hood open ,with out ay street lights, no lights of any kind..start it up and watch for arcing around the dist cap or the spark plug wires.
fuel injector o rings ,R n R get the kit either from the dealer or local auto parts store kit has all o rings for the ijectors (2 each) as well as the fuel pressure reg.
If you have quick disconnects om the fuel line going to the fuel rail check for leaks there...there will also be one going into the FPR