That is the question.
The motor is a F22B1 2.2L I4 with 185,000 miles and has not had any major work done as far as I know (but has relatively new plugs and regular oil changes, and Im not sure but may have had head gasket replacement while it was with the previous 2 owners...). A buddy of mine just ran some seafoam through his 99 TL (1can in gas tank, 1 can in crankcase, 1can in intake manifold) and says that his car has much better throttle response and has pulled harder than ever.
So I did some reading on various forums and most of the people swear that seafoam is a miracle while some see it as another snakeoil (if it aint broke why fix it?) and then there are some who report loss in compression and mis-firing after a seafoam treatment (which supposedly is due to "too much cleaning" that burned away the carbon deposits that were actually keeping gasket leaks plugged up in older/high mile motors that allowed it to keep compression).
here we go:
friend helping with the suction
We went to one of the massive Chiefs/Royals stadium parking lot (Lot L) and basically drove in a huge circle on the periphery of the lot in 1st gear between 3500 and 5500 RPM burning off the seafoam, producing a massive trail of smoke. Unfortuantely no pic of the GIANT smoke cloud that was produced afterwards since we were both in the car.
But I really could not tell any difference afterwards. The motor 'sounds' smoother but it seemed to not pull that much harder but then again these small 4 bangers have little torque at the lower RPMs for the 'pulling' sensation.