Hello, By what you are saying it sounds like a misfire.
You were right to try the spark plugs first.
Have you got the spark plug leads on the correct way (the correct firing order).
Then it could be the coil pack. There is a routine for checking this if you want data and diagrams email me.
It could also be the MAF sensor
or Injectors.
HOS sensor
or the ECM
all the above could cause the problem and the only way is to check them all until the problem has been found.
It is good practice however to start with the most obvious first.
chris
January 2006
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