My car is a 2001 Jaguar S type with the 4.0 engine and it is kind of hesitating and spitting in sputtering a little bit and mechanic put his Computer and he told me it was 02 sender

SOURCE: 2007 cobalt engine hesitating during acceleration

any ck engin lights could be bad gas or spark plug or coil pack braking down

SOURCE: 2000 lincoln ls cracked head???

Previous to 2000 Ford had a cylinder head gasket problem with some of the v6 engines failing at two cylinders at opposite corners of engine (don't know what engineyou have) They supposedly corrected that, but I'm not sure how well the correction worked. I doubt if the cylinder head is cracked but if some amount of compression is getting into cooling system it's possible that it may give you strange sensor readings. When testing, it's also possible that some air escaped and returned everything to "normal" ('till it builds up again).
At this point, I would get a second opinion on this. As well as a comprehensive computer scan, have someone do a radiator hydrocarbon test...that will reveal any compression in cooling system from gasket or any other source. (Don't mention that it was checked before, just say what originally happened so objective testing will be done.)

SOURCE: 1989 jaguar xj6 new engine or new cylinder???

At that price replace the engine. Make sure though that you get a warranty for the engine that includes the cost of installation if the new one fails. Most shops will warranty for 90 days which is long enough to find out if there is going to be a problem.

SOURCE: jaguar s-type restricted performance

I had the same problem. Restricted performance and running rough at 3000 RPM. I have an OBDII code reader and found that the problem was in the air mass flow sensor, which is just after the air filter. I pulled this out and found it was dirty and had butterfly wings in it. The last shop where I had the oil changed replaced the filter for me but put in the wrong size. Close but no cigar. Bought some *** Flow Sensor cleaner at auto store and fixed the problem. Get an OBDII reader with the ability to erase the codes. Comes in real handy.

SOURCE: How to put A/C refridgerant into a 2001 Jaguar s

This job requries special tools and training. Have a shop do this job for you and avoid personal injury exposure.