Vi­bra­tion when warm

Car Mechanics (UK) - - Help! -

I own a 53-plate Jaguar S-TYPE 3.0 au­to­matic with 92,000 miles. Start­ing from cold, the car drives nor­mally, but as the tem­per­a­ture gauge ap­proaches nor­mal, the rev counter starts to fluc­tu­ate by about 150-200rpm. This is ac­com­pa­nied by a rhyth­mic vi­bra­tion from un­der the trans­mis­sion tun­nel. The vi­bra­tion is in sym­pa­thy with the fluc­tu­at­ing rev counter. If I try to ac­cel­er­ate, the vi­bra­tion gets much worse. The prob­lem will some­times ap­pear un­til the car is thor­oughly warmed up, af­ter which it will per­form nor­mally, even if the car is left for sev­eral hours. If the car is left to go stone cold – overnight, for ex­am­ple – the prob­lem re­curs.

I have found two ways around the prob­lem. The first is to come off the ac­cel­er­a­tor, let the car coast, then reap­ply the throt­tle. The sec­ond is to man­u­ally select a lower gear, drive for a short dis­tance, then re­s­e­lect Drive again. How­ever, as time has gone by, the prob­lem seems to be tak­ing longer to dis­ap­pear. Stephen Hayes

One com­mon fault with the S-TYPE V6 is fail­ing coil packs. How­ever, when they do fail, they are more likely to give a pos­i­tive mis­fire and trig­ger the EML to il­lu­mi­nate. An­other com­mon and dif­fi­cult-to-di­ag­nose prob­lem is that the small el­bow breather pipe un­der the rear of the in­let man­i­fold has a ten­dency to per­ish and al­low a vac­uum leak from the sys­tem. It re­quires the in­let man­i­fold to be re­moved to en­able the pipe to be re­placed, and if this pipe has failed then it would also be worth re­plac­ing the spark plugs. The spark plugs on the 3.0 are long-life, but can only be re­placed with the in­let man­i­fold re­moved.

One way of de­tect­ing if this pipe has failed is to use a carb clean­ing spray around the back of the en­gine while the car is run­ning. If the spray finds its way into the com­bus­tion cham­ber via any vac­uum leaks, the en­gine note will rise.

Al­though you do not men­tion the EML be­ing il­lu­mi­nated, you may find that a fault code has been logged. Us­ing a code reader to re­trieve any codes may also help pin­point the source of the prob­lem.

The In­di­vid­ual coil pack as fit­ted to the Jaguar V6 en­gine.

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