instead of the rec. 91? What kind of problems can this cause? Thanks

 

the car will retard the timing to compensate for the lower octane, but the 87 octane can cause knocking and pinging when the car is under load. This can lead to damaged head gasket and other damaged components. also the car won't perform as well as it should.

 

The mild knocking (detonation) under load is what causes the ECU to retartd timing (the knock sensor hears it even if you can't). It will happen cause the motor is 11:1 compression ratio (very high). As bobby said, it will reduce performance as well as fuel economy, which negates using cheaper gas in the first place. This is why it's best to run premium in a motor that is designed for it.

Detonation kills rod/crank bearings and rings. In extreme situations it can even melt your pistons...

 

eventually all kinds of problems, you may notice nothing at first. my opinion, and ive said this once in the TSX forum, if you can afford an newer Acura you can afford 91-93 octane fuel. don't take that the wrong way. i just work at an Acura dealer and see people come in everyday complaining about the extra expenses they forgot to take into concideration when buying their new car (services, parts, gas etc.).