Hi all, trying to get my old girl sorted over the easter weekend so I can start using her a bit more. She doesn't like sitting, and tends to sort herself out once being used, but as soon as it's not getting used it just starts going mental.

Once it's given a jump it fires but won't stay running. Holding the foot on the accelerator it's fine, but slowly ease off and it goes down to 500rpm and starts coughing and spluttering. However once it gets warm, it runs fine. Sometimes it'll cut out at a junction when you least expect but it'll fire straight up again. Incredibly annoying.

A couple of years ago I had a similar issue, and changed the idle control valve, but can't help thinking it's a bit deeper than that. Noticing some recent posts, I wondered if the fuel filter or crank sensor would affect this?

Kind thanks

Dave

 

Hi Dave,

I'm sure others will offer additional ideas, but I suspect you have multiple issues and that the car needs some thorough servicing. Here's a short laundry list of things that should be checked:

In general, Jags do not like to sit, and they don't like weak batteries at all, so if you are having to jump the car, you know you have a weak battery. But you probably have issues with poor battery charging due to corrosion on the battery power connections throughout the car, at the battery itself, the fuseboxes, at the engine bay bulkhead, starter, alternator, etc., and also at the ground points throughout the car. These connections are identified in the electrical manual which is available in the download section of this forum.

The fuel pressure regulator (FPR) is a prime suspect when you're having starting problems and have to keep the accelerator pedal moving to keep the car running. The FPR is supposed to maintain sufficient pressure in the fuel rail (approx. 40 psi but it varies between idle and load). When the FPR loses its ability to hold fuel pressure, the engine can be starved of fuel unless you tell the Engine Control Module (ECM) to increase the injector on-time by pressing the accelerator pedal. One easy test you can do is to pull the vacuum hose off of the FPR and check for the presence of gasoline when you crank the engine. If any gasoline appears at the vacuum connection, the diaphragm in the FPR has failed. But even if you don't find gas leaking through the vacuum fitting, it is very likely that your FPR is no longer holding sufficient pressure. The photos at the link below show where the FPR is and how to disconnect and replace it:

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Besides a failing FPR, another issue associated with stalling is low transmission fluid. Check to ensure your fluid is right at the HOT line with the transmission hot from a good long drive, the car on a level surface, the gear selector in Park after having been cycled slowly through all the gear positions (R, N, D, 3, 2, 1), and the engine running (and idling if possible). Too much fluid can cause similar problems, so if it's overfull you should remove some fluid with an inexpensive fluid transfer pump (less than $10 at an auto parts store).

If it's been a while since you did a basic tuneup, then of course that will help: air filter, fuel filter and spark plugs in particular can all have a direct impact on the symptoms you describe (fuel filter especially if water has condensed in the fuel tank or ethanol in the gasoline has absorbed water while sitting).

Others may mention the Throttle Position Sensor (TPS), which conveys the position and rate of closing and opening of the butterfly valve in the throttle to the ECM. There is a good chance your TPS needs to be serviced (and possibly oriented (calibrated) by a dealer), but the issues that I would suspect and address first are battery charging (replace the battery only after you've cleaned all the power and ground connections or your new battery may not be properly charged), FPR, and transmission fluid level, along with basic tune items such as fuel filter, air filter and plugs.

The photos below show how I serviced the battery power connections and ground points on our '93 XJ40, which differs from your '97, but it will give you an idea of what is involved. The X300 electrical manual will tell you where all the connections are in your car. I know it looks like a lot of work but keeping these connections clean has made our car far more reliable:

Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page

I'll look forward to the input you receive from others.


Cheers,

Don

 

That's great, thanks for your reply! I've got my work cut out - i'll let you know how I get on!