my 2001 S-Type jaguar wont accelerate and shudders

[Rod Baker]

My 2001 s-type jag doesn't accelerate over 4000 rpm and shudders. It won't go up hill as it dies due to lack of rpm's 

[Mark Five]

It could be any number of things. Do you have any warning lights or messages? It needs taking to a mechanic to get it diagnosed - could be fuel starvation, bad coils/plugs. a really dirty air filter, gearbox issue, the list goes on..

[JustBadly]

This may be a coincidence but last week I added 'STP 5 in 1' petrol system cleaner to my Jag. This made quite a difference it is more free-revving and warms up quicker. Any probs with starting etc and I recommend this over everything else.