Intermittent starting issue

The car will often not start for no apparent reason. If left 20 to 30 minutes it will usually start right up, but not always. Battery and all electrical systems are working fine. It is as if the fuel is being cut off (anti-theft devise?)

Turn the key no sound, lights work horn blows. Radio works

Electrical problem
2001 Jaguar S-Type 6 cyl Automatic 118000 miles

2 weeks ago, I got out the when I removed the key from the igntion I notice the car was stil running! A mechanic that changed the ignition swithch in Nov told me he witnessed this with my car, this was the first for me! He advised me to pull fuse 18 under the hood if this ever happens, so I did. I started the car drove home and it wouldn't start. Another mechanic told me it was the electircal portion of the the ignition switch (the other portion I previously replaced was cylinder shaped). I purchased the part and he called me and told me the car starts now, but won't shut off unless the fuse 18 is pulled, his I drove it to a shop that usually does the maintainence on the car, it was after hours, they told me 2 days later that the car never started for them and they believe it is a problem with the security system / computer and it would need to go to the dealer. I planned to trade the car in this weekend. In the past year I've changed 2 ignition coils, O2 sensors, igntion switch ball joints, rotors, brakes and tires, andwindow regulators the car is very well maintained! Please advise me of some things I should check before dropping big money into repairing this pretty headache of a car. Thanks.

If the car is left for more than 10 minutes, it has a tough time starting. Usually it takes 2 cranks to get the car started. I would smell gas or exhaust during the starting period, but then it runs perfect. Note if I turn off the car then trying to start it within the 10 minutes everything starts properly. Also if I disconnect the negative terminal for 20 seconds to reset computer, the starting problems are solved. Then after a couple of days somehow the starting problems comes again. I've already replaced the ECT sensor with no change. Whatever the problem is, it is time sensitive Please advise

Electrical problem
2001 Jaguar S-Type V8 80000 miles

The car has been sitting inside the garage through the winter, It had a weak battery before the winter and had no power when I went to start it. I confirmed the battery was dead and replaced it. I went to start it up and it started right up.I moved it out of the garage to clean out the back seat and after went to start it but it didn't fire up!
It cranked very strong and I have full electrical power. I checked the fuel rail and I didn't get any spray when I pushed in the check valve with my key. Can there be any other possibility besides a fuel pump? The car had a full tank of gas before the winter and still does. I never had a problem before except that if the car sat a few days it cranked slow sometimes I needed to boost it (that's why I changed the battery). But it never ran funny after it started.

Thank you! I will try it tonight and let you know what I find out.

Could this have anything to do with the Anti-theft system, I only have the valet key.I had to change the battery by folding down the back seat (I attached an access cable when I lost the main key for just this purpose!)

I tried it the next day and it started right up before I could check anything. I tried to restart it several times and I had no problems. Strange. There is no engine light or anything, could it have had anything to do with the fact that I didn't start it for 3 months or so? Any ideas in case it still could be a problem that might come back?

My alarm was tripped by mistake. Car started and then stop running. Gear shifter wont lock into place-neither will sterring wheel lock. Disconnected batt- hopeing that system will reset it's self? Car is like new.

You mean after the battery was replaced, and it started and it still needed to relearn? Interesting.

Try using the key fob and hitting unlock buttom to disarm system. Try any additional keys you have to see if it starts with them. Is the PATS LED on the center of the dash flashing?

Sounds more like the plugs fouled with petrol as it never run for long enough to warm up, leaving it overnight allowed the petrol to evaporate and so it started up again.

I have a 2001 Jaguar S-Type with 55000 actual miles.
Car runs great, but problem is in the start-up. After sitting for 20-30 minutes or more, starter must be engaged for 5-6 seconds before engine will fire. This does not vary. Have had car to a Jaguar repair service center after used car dealer where purchased could not find the problem. Fuel pumps were replaced as well as the fuel filter EGR Valve, some clogged tubing, etc. Fuel tank was cleaned as well. Service center stated the fuel in tank was comtaminated. Fresh premium fuel was added. So far, the original problem still there. Any Ideas?