 What is the right fuel?
I am deciding to write this for information use only, if you care to comment please go ahead.
Some people have the misconception that upgrading to higher octane fuel will always improve the performance of any vehicle, especially under adverse conditions (like winter).This is only partly true.
Higher octane fuel will improve performance it the engine is of a high compression design or it the load placed on the engine stretches its anti-knock features to the limit.
This is because the purpose to the additives in higher octane fuel is to increase the octane level to slow down the burn rate of the fuel. This works well to prevent pre-ignition on higher compression engines(or older, carboned engines). As you know, pre- ignition occurs when the combustion chamber temperature/pressuer gets high enough to cause the fuel mixture to spontaneously ignite without the spark plug (like a diesel). The pinging that you hear is the shock wave created by the collision of the flame fronts from the spontaneous burn and the spark plug burn.
So, when and why would you NOT upgrade to a higher octane fuel?
On lower compression engines, under normal operation conditions, there will be no advantage to using higher octane fuel, just additional cost.
During cooler engine operation conditions, higher octane fuel will actually have a negative effect on the engine's performance. Under EXTREME ambient conditions(-40f) the engine may not even start.
Normally, however, the first indication of a problem that you might notice is a longer cranking time before the engine starts, usually when it is cold. This is because the higher octane fuel in MORE difficult to IGNITE.
As an emissions issue, the high octane,slower burning fuel may also not have the time to burn completely during the piston's power stroke. This means that some raw, unburned fuel may be expelled into the exhaust system. If the vehicle were to be driven on a number of short trips, the engine may not get warm enough to go into"closed loop" for a long enough time( and the oxygen sensor could identify a rich exhaust mixture0. The catalytic converter could in this case then, become "flooded" with fuel and permanently damaged.
So there you go. There have been some posts about hard starting and driveability concerns so this may or may not be the problem, BUT worth trying out. | 
