Having a confluence of issues with my Six at the moment and unsure if related. I first encountered problems with the revs plummeting as I came to a stop, with the car struggling to not stall. This developed into occasional stalling when stopped at lights. I now also have the issue that the car is very hard to start - with it cranking for a fair while before catching and immediately dying three or four times before I can get it to run. Unsure if related.

Other than a lumpy idle, the car runs well when going with no hesitation and plenty of power.

My first thought was the CKPS, but the car does show 200rpm while cranking so is that ruled out? I’ve cleaned the TB and IACV with no improvement. Battery is very new and cranks at about 10.75V.

Not sure where to go next…

 

You should check for a vacuum leak somewhere. Could be the intake manifold gasket giving away.

When was the last time you replaced the oxygen sensors?

Is the Coolant Temp Sensor original? Less likely, but a $20 part and 5 minutes of time.

 

Square body X40 series or curved body X300 ?

The fuel pump may be under performing as most critical at idle and start , has to do with minimum injector pulse width or open time

Main fuel filter change , injector cleaner in the tank ( Chevron brand ) inspect the fuel pump motor connector for burnt sockets and swap the fuel pump relay as they can have the power contacts inside burning / pitting , both signs the fuel pump giving up the goast , 43 psi fuel pressure

The CKPS on this model can show tach , but fail in the single signal being discerned in that one use of fuel pump enable

 

Parker's question is a good one: is your car an X300 with AJ16 engine or an XJ40 with AJ6 engine?

Both have the ZF 4HP24 transmission, which has a known issue of low transmission fluid causing engine stalling when slowing to stop or make a turn.

A common place for a major intake air leak to form on both the AJ16 and AJ6 is on the underside of the air intake elbow where it connects to the accordion hose that leads to the throttle body. If the hose clamp is over-tightened at all, it can cause the underside of the elbow to bend inward, opening a large leak for unmetered air, causing very lean fueling.

If your car is an XJ40, there is an onboard diagnostic system that may help. Please let us know which car you have.

Cheers,

Don

 

You might also want to look at the deep spark plug wells that extend from the holes in the cam cover into the cylinder head.
I recently bought a 1997 X300 where the cam cover gasket and the spark plug seal gaskets had not been changed for years and years.
As a result there were huge amounts of oil down around the plugs. In some cases the plugs were completely submerged in oil.
You would remove the screws holding the cosmetic panel that covers the six coil packs, unplug the wiring connections from each coil pack, and then remove the two screws holding each of the coil packs down to the cam cover.
Once you do all of that you can pull each coil pack out so you can look down in around the spark plusg to see if this might be your problem.

 

It’s an X300 yes. Early - 11th off the line apparently.

I have a CKPS arriving tomorrow so we’ll see if that makes a difference.

 

There was a recent report (s ) of generic or low quality CKPSs have a spot of stumble under the bonnet so a word of caution

A good ( or at least in this test variable) CKPS will read 1300 ohms

Fault code CEL P0335 if it even shows

You can directly power the fuel pump with a jumper between socket 3 and 5

Best to use a medium wire with blade type wire ends or you will be short coming the proper current to drive a in question pump , the store can make one for you

At least keep one in your kit least a tow bill

This will be on at all times with key in pocket

 

I had a similar problem with my 96 A16 engine. I ended up changing the crank speed sensor, transmission control module and the engine control unit. It's been working fine since.
After that I'm out of ideas.

 

That's not diagnosis, it's the "Parts Cannon." We discourage that around here because throwing parts at a Jaguar can get very expensive and time-consuming without resolving the underlying problem.

Either the ECM or the CKPS may have been your problem (probably not both). The TCM has nothing to do with engine startup.

Cheers,

Don