STP and STP only.
Not a gimmick works after 20 km travelled. It is worth using and it will not damage anything.
The one thing to remember is that if your injectors are plugged than the car does not start right away in the morning. It takes a moment longer.

Seafoam is rather carbon remover than injector cleaner. You can try that too. It works after 1 or 2 weeks and cleans the fuel system. Engine sounds like fresh from the dealer.

 

cool - thx Adam

 

If Crankcase ventilation system goes wrong than you feel like you are driving a tractor. The symptoms appear when the engine is hot only. He has little vibration.

Somehow I feel like checking the battery. How old is it? How many Volts appear on the dash 13 or 15?
In case this is closer to 15 the engine could be trying to charge it.

 

Dynamite Kid - this is the PCV fix I was referring to - BSH Bulletproof PCV Revamp - BSH Speedshop

Is the PCV easy and cheap to replace? I owned a 2.2L Honda prior to this car and the PCV was easily accessible and $4 to replace. This is a whole new engine to me, I have no idea where things are situated.

 

i use lucas fuel injector cleaner. You can get it at canadian tire or walmart.
Works every time for me.

 

Thx kf3506

 

Yes Lucas works and also lubricates.
With this one:add to full tank only. It is oil.
It is not as strong as STP. It does not clean the sparkplugs and may make them oily. If you have new sparkplugs it is OK.
In any case if you have not used fuel injector cleaner before, go ahead with either or. It will only help.