What causes an engine not to idle?

This in in Non-tech becuase it is about my ZJ, however, since it is the same 4.0L I-6 as most of the XJs have, I would bet the answer would be the same if I posted it in OEM tech!

My 1996 ZJ starts right up, but then won't idle. It just automatially dies right away. I can start it up many times over and it just dies, so the starting isn't the issue.

I can drive it if I keep my foot on the gas and keep it about 1000 rpm or higher, all while using the left foot to operate the brake.

Not a great idea, but I did what I needed to in order to get home.

Any thoughts or ideas on why this would start and then refuse to idle? FWIW, I did change out plugs and wires, fuel filter, and transmission filter and fluid a couple hundred miles ago. This is the first issue I have had with it since the work. Truck has 201XXX on the clock.

Thanks!

The idle air controller controls the idle speed. It is controlled by the ECU. You can pull the IAC, clean it carefully with a toothbrush and carb cleaner. Then spray the throttle body cavity with carb cleaner and use qtips to clean the hole where the pintle seats.

Sounds like a CPS issue.

Should be moved to Other Tech.

crimsondragon said:

Sounds like a CPS issue.

Click to expand...

What makes you think it is a CPS issue? There are two main failure modes of the CPS. The first is no spark at all, the second is that it will start and idle but won't run at higher rpm's. If the CPS had problem with low rpm's why would it start, which is an even lower rpm?

My brother's XJ did the same thing.

Turned out to be the TPS

I'd bet on TPS or IAC also... no way could it be the CPS, those fail by either not working at all, or not working once they warm up a bit.

Could also be fuel delivery I guess, but not likely.

Not sure what the issue was, but it ran like a champ today. I am sure something is fixing to go south, but for now I'll just keep an eye on things.

This is kind of common when the IAC gets dirty. It sticks or the orifice gets plugged. It can't hurt to clean it.

Clean the IAC or replace it depending on how bad it is. If that doesn't change anything replace the TPS.

Even if you replace the IAC you need to clean the cavity behind the sensor.