I think I have fouled my spark plugs already! They were the AC Delco rapid fire plugs. I think it might have happened when I ran throttle body cleaner in the throttle body, and sea foam through the vacuum system. still, is this possible to foul them that soon? Just asking because my gas mileage has gone from 28/29 to only 24/25 with no change in my driving habits. Just trying to get the best mileage possible and hoping it'* just something as simple, and as cheap as spark plugs. The 02 sensor is less than a year old, so I'm hoping that'* not it..

Which model spark plugs do you have exactly? It is possible they're fouled, or offer degraded performance, if they're copper plugs.

If your car has no mods then you would be best off with Iridium plugs.

Cheers,

Can you post pics of them?

what kind of throttle body cleaner?
Is it intake and gasket safe?

says right on the bottle safe for throttle body/sensors. I'll probably just get some new plugs. maybe some AC Delco platinums. Don't know yet.