OK, no start unless pedal is pushed

Yes, I did search, but found nothing with similar symptoms.

96 cherokee sport, 4x4, 4.0, aw4, cali emissions

Now, the last few weeks or maybe month, I have noticed sometimes the jeep wouldn't start on the first try, but always did on the 2nd. Maybe 1 out of 8 ttimes it did this. I attributed this to the loose nut behind the wheel letting go of the ignition switch too soon.

Now, today, go out to go to work and no start, turns over fine, but no start.

Jiggle the trans shifter, and even try in neutral. No help

Ok, go out under the hood and check the fuses/relays. Even move some around to see if it helped. No difference.

Checked the coil wires. Good

Now, get back in and just for grins, try to start it with the gas pedal depressed....and it starts. Runs a little rough, but does run. Will not run below 1000 rpm. OK, at least I can move it without manual labor.

Now, what would be the diagnosis...I am thinking either IAC or TPS (or both).

While I do have another jeep to use, this is my daily driver and I need to get it fixed quickly.

Any advice or tips would be greatly appreciated, especially if it solves the issue, since my work schedule makes working on it during the daytime hrs difficult.

ASD relay is most likely the problem. It leaves the computer running for a few seconds after the key is shut off so it can reposition the IAC to the correct position for starting.

Tried 3 different relays in that spot, no difference.

Seems to be running and starting ok now after flushing the crap out of the IAC (like 1/2 can of throttle body cleaner thru it running and not).

I never new that about the ASD relay

Does actually pushing the pedal do anything on fuel injected jeeps ?

don't know, but it did let mine start.......

I would think the TPS tells the computer as soon as it is rolling over that it needs more fuel, but I ain't no expert

dobesrgrt said:

I never new that about the ASD relay

Does actually pushing the pedal do anything on fuel injected jeeps ?

Click to expand...

The IAC parks partially open and gives you enough air for a start. If it sticks shut and the throttle plate is closed, you get no air. A little throttle gives you enough air for a start, then you have to work the pedal gently to keep it running.
Normally you don't need any pedal, unless the IAC is stuck shut for whatever reason. Sometimes a really weak battery can cause the IAC to be iffy, sometimes it is sticky deposits. Sometimes the grease packed inside the IAC motor gears gets crispy from heat and age. Sometimes it is a little of everything.

The idle air controller on the side of the throttle body is probably sticking. On fuel injected cars, the gas pedal just opens the throttle body blades to let air into the manifold, then the computer applies fuel to match. The idle air controller is supposed to pass air for you below a certain speed, when it sticks you get symptoms like described. If holding the pedal down makes a difference then you're basically bypassing the idle air controller

That was my thinking, just wanted to make sure I wasn't out in left field on this

On a side note, it did force me to drive the 88 today, ain't done that in several months

Having to tip in the throttle to start can indicate a bad throttle position sensor.

And cleaning the idle air control is never a bad idea. Clean the throttle body while you are at it, as both get carboned up over time and miles.
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The Idle Air Control (IAC) is mounted on the back of the throttle body. The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is moved in, the air control passage flows more air which raises the idle speed. When the valve plunger is moved out, the air control passage flows less air which lowers the idle speed. Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea.

CLEANING THE JEEP 4.0 IDLE AIR CONTROL

Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a torx driver (2 bolts; one can be kind of hard to get to)

“Gently” wiggle out the IAC from the throttle body. Gasket on the IAC can be re-used if it is not damaged

Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and is best for this task. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it.

Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner

It is also a good idea to clean the entire throttle body itself, the butterfly valve inside of the throttle body and all associated linkage as long as you have things disassembled

Reinstall IAC and check idle quality

Then what does the TPS do compared to the IACV ?

The TPS monitors throttle blade angle so the computer knows where how much skinny pedal is being applied. For example, the computer goes into a bypass mode when the driver has the pedal floored. Also the trans computer will shift differently based on how much pedal--it will shift sooner and smoother when light pedal, and shift later and faster when heavy pedal. A bad TPS can certainly cause some weird problems from the jumpy voltage, but the problems described by the OP point directly to the idle air controller.