Originally Posted by TerminatorX5

replace all coils - at least as preventative... this is what i had with bad coil on cyl 5 (4.8 V8) - the car idled kind of ok... slight "murmur" instead of pure purr... driving was ok, as long as i did not push over 2500 RPMs... as i pushed over 2500 the car was "undercutting", as if in a hand combat, somebody hits you hard iin the area just below the chestplate, and that cuts off your breathing - the pedal would hit the floor, the RPMs will surge from 1200 to 2500 and instantly back to 800 and rebounce to 1200 while the car, instead of launching, would actually slow down (if it were rolling and i need to merge, it would not merge). straight outright scary... no engine light... until i drove on long uphill where i had to keep engine running at higher RPMs, the engine light flashed, and finally just stayed on... i had my laptop connected at all the times, and cyl 5 was acting up all along... the moment i stuck in a brand new Bosch coil, everything came to normal...

Go to fleabay, look for INPA... it is the factory software that will let you diagnose many aspects of the car...