85 xj6 4.2 will not idle. will start and engine will stay running as long as the throttle is being engaged. As soon as i let off throttle it dies out. If anyone has any ideas on where to start please let me know.

... quick history and what ive already done. Car ran fine 8 months ago before i parked it ( oldest story in the book i know ). Initially car wouldnt turn over at all. Fuel pump had seized, wouldnt engage upon ignition. Changed fuel pump and filter. Was able to start it but would die out once i let off throttle. Drained old gas from both tanks. Changed filter again. new gas and some primo injector cleaner ( BG 44k) to clean up injectors. Ran for 10 min while holding throttle at about 1500 , as soon as i let off, dies. Changed air filter. Also i should mention new MAF box a few months prior to parking. A buddy told me that the air fuel mix may need to be adjusted but I dont see how the adjustment would be off. Thanks again for any pointers or ideas.

 

Does this happen if you start the engine when it is already hot? I wonder if the AAV (auxilliary air valve) is stuck shut, or is not getting the correct info from the thermotime switch to make the AAV open when the engine is not hot.

***THIS post contains errors. The Thermotime switch operates the Cold Start Injector not the AAV.

 

yeah i held throttle running for quite a while to clean injectors and same issue. But you bring up a question. If the thermotime switch was bad. would it run at all? issue seems to be only at idle. Any thoughts on fuel temp sensor causing issue?

 

The thermotime switch reads coolant temp and sends signal to the cold start injector, not the AAV--SORRY for the bad info. It only operates while cranking so it won't prevent the car from running.

The AAV contains a bi-metal strip to sense temperature on its own and reduce idle as the engine warms.

If there's a fuel temp sensor, I don't know where it is!

Can you do a fuel pressure test, maybe the fuel pressure regulator isn't keeping pressure up in the fuel rail. Or an air leak into the intake manifold at some point after the MAF could make the fuel mixture too lean.