Hello can anyone help to diagnose an

engine shutter when schifting into high gear under normal load rpm between 1200-1500 /42-45 mph / light throttle already replaced tranny @76000 miles model s-type year 2000 no ce light no faults

 

Which engine?

Probably an air leak or bad coil.

 

sorry it took so long engine is 3.0 what does an air leak mean? also how do we determine which coil?

 

More than likely an air leak (check fuel trims at idle and 2,500 RPM as JagV8 typically advises) as far as to how to identify a misfiring coil under load - easier said than done.

First things first - check the spark wells for any signs of oil - if you find any - you need to get the cam cover gaskets changed out ASAP.

You can purchase a COP tester to test each coil at idle.

 

A petrol engine is a creator of vacuum as it runs so "air leak" means a leak of air into where the vacuum should be. It ruins all sorts of things so would need fixing.