Is the gas cap on the drivers side or the passenger side? This will often tell you where the car was built, drivers side=USA. If the cap is on the passenger side it was likely built in Japan and this is the problem, as the Japanese built cars are made from sub standard, recycled pot metal. In the latter case, you will have trouble for the life of the car(or as long as you own it). It is unlikely that a sensor would be bad without a code coming up. It is more likely an issue with a plug wire, coil pack, improperly installed or torqued plug, improper plug gap, injector fail, or warped cylinder head/bent valve. These problems while minor are often costly to repair, as the only way to diagnose is to just keep throwing money at it until you get the right thing. I prefer to keep my cars in the following guideline. K.I.S.S., Keep It Simple Stupid. My cars are often older, and all mechanical. Very simple to diagnose and repair, cheap too. And for the same price of a new car, you can buy and completely restore an older one often with money left over for new guns!