Just bought a low mileage XJ40 4.0 that's done only 65 miles in the last 5 years on driving it home after approx 20 miles the gearbox and check engine lights came on and went into limp mode, I have checked the plug on left of box car starts ok then runs rough and cuts out then will start again and run for a few second then cut out what should I do next ?

 

Hi pa-cresta:

First, welcome to the forum! Be sure to introduce yourself to everyone in the intros section. We try to be a really friendly place and love to meet all of our new arrivals.

Second, sounds like you've found yourself a very nice car. Don't panic that it's already acted up. These things can be resolved - sometimes easily. In a way, that first repair is like a rite of passage. My XJ40 ran for exactly 5 days before dying - which put me not only without a car to use but also with a huge existential and automotive crisis. (What had I done, purchasing this thing?!?) All is well…

Here's a link (found in our 'sticky' section) to the great step-by-step "limp mode" troubleshooting explanation from Jag-Lovers. Because of your hard starting/running, I'm especially suspicious about step #4 - the throttle position sensor/potentiometer. I don't have any personal experience replacing or adjusting it, but others here do and will undoubtedly chime in. You may even find related threads discussing the TPS in prior posts. This at least gets you started:

Jag-lovers' Ebooks

Take your time and let us know how it goes!

Cheers,
Scott

 

pa-cresta,

Welcome to the forum.

First a few questions:

What year is the vehicle, and what is the Vehicle Identification Number (VIN)?

What's your experience level in troubleshooting? That tells us how comprehensive our explanations need to be to you.

Based on your intro, there could be a variety of issues, especially since it has been sitting still for virtually five years.

Go to the link Midwest supplied and review the information, then respond back so we can help.

 

Hi pa-cresta,

The most common cause of Limp Home Mode (LHM) on our '93 has been oil contamination of the electrical connector for the Throttle Position Sensor (TPS). The TPS is mounted on the underside of the throttle body and its variable resistance indicates throttle position to the Engine Control Module (you guessed it, ECM).

On our '93, the electrical connector for the TPS mounts to a metal bracket affixed to the intake manifold near the cylinder 2 or 3 air intake elbow. The connector can be unclipped from the bracket, I think by carefully pulling out on a plastic tab. Be careful, because the plastics all get brittle with age and heat. Disconnect the two halves of the connector and flush it out with electrical contact cleaner spray. Allow to dry, then reconnect. Start the engine and see if the LHM lamp goes out.

If the LHM lamp remains illuminated after 30 seconds, then you'll need to explore further, so follow the link Scott provided to the diagnostic procedure in the Jag-Lovers eBook. I have photos of some of the components involved, so let us know if cleaning that electrical connector doesn't help.

I'm adding a link below to photos showing how I cleaned our TPS by removing the throttle body but not disconnecting the TPS from the throttle body (the adjustment of the TPS on the throttle body is important, so don't disturb it unless you learn that you have to). You can see the electrical connector for the TPS in the photos. Your connector may look different, depending on your model year. Oil contamination of the TPS itself is also a possible cause of LHM, which is why I drilled the drain holes and flushed it thoroughly with contact cleaner.

And as Rob mentioned, it will help us help you if you will add your car's year, model, engine displacement and mileage to your signature line, since different model years and engines have different components.

Cheers,

Don

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