Cherokee Idle Issue

ty20404

Member
Joined
Feb 14, 2011
Location
Wilmington
Okay, I'm going to be as systematic about the details here as possible because I've got a baffling issue that I dearly need help on.

My idle drops to about 200 RPM when: I am braking without the vehicle in gear from any given speed. Typically happens MORE OFTEN and is more noticeable when: I'm going downhill OR from a higher speed than ~30 MPH.

Details on the vehicle: 1996 Cherokee Classic, AX-15, 4.7L Stroker. ~230K miles on body/trans, ~40k miles on engine (second hand Precision Engines crate motor). I have upgraded to a Comp Cams package (the one for Fuel Injection).

What I've done so far to TRY and fix the problem: Replaced Fuel Filter, Replaced Injector O-Rings, Replaced TPS with used TPS from my old 2000 XJ.

What I'm thinking: I'm thinking there's an issue with the fuel delivery system... I say this because I doubt there is a vacuum leak issue. I do NOT get any sort of idle issue while at a stand still and stepping on the brakes. Whenever I have the hood popped and I rev the engine up and release the throttle there is not a single idle issue what-so-ever. I also don't think it's the IAC valve because I cleaned the ever-living-shit out of it, and if it were the IACV I would probably notice idle issues across the board...

I'm thinking it's something having to do with the gas tank/fuel pickup/fuel pump but I have zero experience in this area, so any insight on where to start would be great.
 
transman731 said:
after cleaning the iac, did you reset it?
have you checked the one way valve in the brake booster?
Click to expand...

How do I go about resetting it? Just clear any codes in the computer or unplug the battery for a while?

I'm unfamiliar with the brake booster but where is the one way valve in this? Have any quick links on hand illustrating where this is or how to clean it?
 
I would start with the TP and IAC. I know you tried another one, but I suggest to actually check the voltage at the TP with the throttle closed. Key on, engine off, one wire will have 5v, one ground, and one should have 0.8-maybe 1.0 volts. If it is much higher than 1 volt, it is no good. Also, start the engine and see if the voltage flunctuates at idle. You may see a intermittant voltage increase from a bad TB.

Also, the IAC solenoid is continually actuating, really tough to "see" it fail. Your symptoms are inline with a bad IAC. Really, for the cost, I'd swap in a known good IAC.

Report back, I'll help all I can.
 
Anyone have a functioning IACV laying around in Raleigh? I don't mind buying a new one, but I'm a college student and cash is tight so I don't want to buy a new one and have it not be the problem?
 
transman731 said:
i'm sorry, i didn't realize you were in raleigh. you are more than welcome to come by the shop and i will check it for you. the shop address is 6826 old wake forest rd (near triangle town center)
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It just doesn't get any better than this! Thanks for being, Lee :driver:
 
transman731 said:
i'm sorry, i didn't realize you were in raleigh. you are more than welcome to come by the shop and i will check it for you.
the shop address is 6826 old wake forest rd (near triangle town center)
Click to expand...

Thanks Lee, I'm going to take you up on this. You replaced the 5th gear in my AX-15 this summer. She's finally moving now and this is the only remaining issue with her. I'd love to stop by and learn a thing or two about the brake booster. I know all too much about everything else with a car, might as well learn more. Any chance you'll be at the shop Saturday? I've got two exams tomorrow... I could always stop by Monday if not.
 
Well I picked up the cleanest IAC valve that I could at LKQ and it doesn't seem to have fixed the problem... I also checked that valve that comes out of the front of the brake booster and it seems to be functioning properly... Not sure what it could be.
 
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