having exceleration problems/ what could cause this

What is your question?

this happen all the time, started off and on about 2 yrs ago had tune up and cat converter put on also, took it to a jag still could not give me the right answere just can not trust this people

What makes this problem better or worse?

can not tell

How long has your 1992 Jaguar XJS had this problem?

off and on 2 years