Ran when parked
An XJS that has sat for several months to a few years can seem like a problem when driven again for the test drive. The first thing you should do is carry some white paper towel with you, check the oil which should be clean if well maintained and you should be able to read the markings on the dipstick through the oil and wipe onto a piece of paper towel and look for any little metal particles. And you thought you were going to a backyard cookout when I said to take a paper towel.
If black and gooey or thick and sticky then this engine was not serviced properly and you should take caution. The transmission as we say in the States but gearbox in other parts of the world should be pinkish and smell like oil but if dark brown and smells burnt then expect trouble in paradise and also wipe onto some paper towel and look for metal particles Now the next thing is overlooked too much. Check the coolant reservoir which may be a yellow or blue color but what you never want to see is something dark floating in it that somewhat stands alone and that is because it may be oil and that is the sign of a leaking head gasket.
Things like the AC and electronics may not work correctly right away from sitting. The test drive should last for as long as you can drive the car on and off the highway as it may take around 15 minutes for it to get warmed up and ready for all systems to realize that the car is running again and begin to function properly. I am going to suggest something that you have heard me say before and that is to allow the car to run for several minutes while parked so the oil can rise to normal operating temperature to lube parts before moving i.e. the lifters and valves from sitting for some time. Unless you know just how long it has sat not driven or even perhaps running, chances are it is longer than mentioned by the owner.
I bought a 95 in Tampa three years ago for parts and I was told that the car sat for around 6 months but when I arrived and saw the license plate still in place, which stated expired 2015, and the fuel smelled so bad that I was concerned when I placed the car in storage until I could have someone pick it up. As for the AC not working most times in a car that was sitting around, and remember the last produced XJS is over 24 years old, I always repeat the same thing that is normally the cure for several things in classic cars that have many times the original hoses, replace, replace and replace. The main place where the AC on these cars fails/leak is the high-pressure hoses. As well the bearings and seals on the compressor ware. We have remanufactured such hoses as AC, fuel-related, and engine oil cooling lines to nearly twice the original pressure ratings. Bearings in the compressor ware from high use and the seals from age.
This is where the AC dye/leak detector is of good use but overall and more than not it’s the hoses from age. The most important thing to remember that is all too easy to overlook is that the XJS no matter what year is 24 plus years old and all rubber must be replaced as soon as you buy the car unless there are service records that show they have been replaced within the last couple of years. And I mean a couple as in two. And remember this, rather than listening to the seller telling you that the issues you find are just this and that but he just did not have the time, I suggest you have on some headphones while listening to Ray Charles hit the road jack. And lastly, there are plenty here in the States to choose from and we are now preparing several great examples to place on our site for sale from our Miami location while building the XJS restoration center on 15 acres in Palatka, FL.