Hi there,
first thing to do is get a compression test done as it is a waste of time doing a tune if the comp is to low, if that is ok, normally you would chance the plugs, air & fuel filter, scan for unresolved fault codes, and in your case check the high tension leads for a fault as you may have a faulty lead on No 4 causing the miss fire, start here.
Mark (mhpautos)
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Sunday, October 25th, 2009 AT 7:07 PM