Friend's car is not running right, need help read post inside
 

My friend wanted to see if he got more boost in the cooler weather. So when driving at cruising speeds and downshift to 4th then 5th gear everthing was fine and the engine sounds as usual and healthy as shit. After 30 min. of driving on the freeway then we headed home at a stop light for some reasons we notice that the idling was really bad meaning it will keep on shutting off unless he gives it a little gas and the exhaust sound different like it is missing a pulse. Well going home the next day we took it up to Dave at KDR to see what is going on. Well he adjusted the idle and take a look at the PFC and he lean it a bit. Well now the idling was fine but Dave also notice that the exhaust sounds different too. So he told us that it is 50% that it is coming from the engine. So is this a sign that the apex seals went bad or maybe there is a false spark plugs or a missfire somewhere. The car still drives hard and he gets 10lbs of boost as usual.

Well to get things out of the way, do a compression check. Right there you will know which fork in the road to take.

If the engine is ok, then YES for whatever reason, it is misfiring. A common problem for us is the electrical connector on the coils. They tend to break and fall apart with age and heat. You may want to start there to ensure they have a good connection to the coils.