Our sons jag x-type most of the time has a hard time going pass 3000 rpm! it will sputter and say cruise control not available! Read other post(seems the ECM or the cars computer would be the fix)but before i purchase that part we just want to make sure that that's the right fix! Can anyone chime in and give me your feedback? Thanks a bunch!

 

Inhibiting to below 3000 RPMS is the fail safe mode to prevent engine damage. Is the Check Engine Light on? You need to have the codes reads and post the DTC numbers.
Also you need to get the fuel trims read STFT (short term fuel trim) and LTFT ( long term fuel trim). STFT at idle and LTFT at 2500 rpm. A code reader is your best tool in the box in trying to figure out a problem on a Jaguar.
Tossing parts at a Jag will eat a very large hole in your wallet before solving the problem.

 

Being in limp mode where the car doesn't rev past 3K could be caused by many different things. Most likley a vacuum leak or misfire. ECM would be low on the list to replace. Get the various codes read and post them here and/or do a search on here as to what they mean and how to fix. Whatever the cause, don't keep driving it like that or you risk making the situation worse. And if teh check eng9ine light is flashing certainly do not drive the car as there would be a misfire so severe to be causing immediate damage.

 

Very very unlikely.

Probably the LAST thing to suspect.

 

The "most of the time" is not a good thing for sure. That means he's been driving in "limp mode" - "most of the time". No telling what damage has occurred (i.e. catalytic converter damage, etc.) For sure get codes read, do a search here on causes and repairs/fixes and don't drive it until fixed.