96 Cherokee-starting,idling problems

[mrst53]

HELP! Before my husband puts a hammer thru the windshield. I have 4.0L that has a couple problems. 1- it will start, but if you shut if of, will not start unless you hold the accelorator down to the floor and then it will not idle down(it thinks it's a toyota) The idle will will stick at times when it is running - like at stop lites and stop signs. He has tried checking on the meters and has come up with 3 different ideas- all of which could cost us a total of $500- we just moved to this area and don't have a good, honest mechanic we can trust.
Do you have any ideas he can try?
Thanks,Linda

 

[MudderChuck]

My 96 wouldn't start, finally went back to my old carburetor days and tried starting it with about 1/4 pedal (didn't want to flood it). It fired right up, but would stall every time I tried to get it to idle.
On a hunch I sprayed some spray oil down the IAC (idle air controller opening) and it worked just fine for about a week. I repeated the spray oil treatment and it lasted almost a year. Now I spray it twice a year, just in case. I sprayed the oil down the IAC opening with the motor running and lightly worked the throttle a little by hand, be careful I almost lost the spray nozzle extension tube down the throat of the TB, which could have been interesting.
Related maybe, my IAC tended to act up worse when the battery was weak (shortly before replacing it). I fugred a combination of gunk in the IAC and lower voltage added up to trouble.
I sprayed the oil into the rectangular (kind of/odd shaped) opening near the top in the throttle body.
I also broke off one of the plastic mounting studs, which was a more involved epoxy glue project than you'd think.
IAC would be my first guess, what you described sounds familiar.
Next best guess would be water in the TPS. Have you bathed the motor lately? Water logged or solvent bathed TPS's have been known to cause high idle and all sorts of other grief. I've never seen it myself on a 96, but experienced it first hand on my 88. I'm real careful about washing my motor now, I avoid getting the TB wet.
Major vacuum leaks can also cause high idle, but in my experiences don't mess with starting much.
If you've run through any big puddles lately, the air filter is worth a look see. They get water logged and the air flow to the motor suffers. I've seen n air filter soaked with water and sucked into a wadded up piece of trash by the suction from the motor.

 

[mrst53]

we have a fuel injector, not a carburator

 

[MudderChuck]

we have a fuel injector, not a carburator

No kidding? But if the IAC doesn't open during starting you may have no air either, so the same techniques used on an old carbureted vehicle may prove successful.
Three things you need for it to start, air, fuel and spark. Too much or too little of any of these will cause grief.
I've had an xj of one flavor or another since 87.
If you crank it long enough, with no air, it can flood.
If you open the throttle all the way during starting, the computer wil shut off the fuel injectors. You are then pumping only air and this may clear the excess fuel from the cylinders, at least well enough to get it to start. I'd then let it run at a steady 2000 RPM for awhile, so the motor cleans itself out.
You have a throttle body that controls the air into the motor, with the gas (air) pedal (along with the IAC at idle) and 6 fuel injectors which supply fuel directly into the intake manifold (metered by the computer PCM, with inputs from various sensors).
I wouldn't offer to much advice to your husband as long as he has the hammer in his hands. LOL
If the exhaust is crushed or the catalytic converter is plugged (has it been making a rattling sound lately, kind of like a tin can full of rocks?) it can cause the same thing. No exhaust out, no air in, kind of like a giant colic.
If the IAC is stuck shut it won't start unless you give it some pedal. If the IAC is stuck open the motor will/can idle really high. The IAC is constantly opening and closing as you work the gas (air) pedal, it can and will stick almost anyplace. It's a small piston opened and closed by a very small electric motor.