First of all I got a 91 Cavalier RS 2.2 with about 245k on it and can not get to idle right. I've replaced the thermostat and the crank sensor and spark plugs and wires and fuel filter and the idle air control valve and the throttle position sensor and just replaced the oxygen sensor and it helped the car some but still not idling right... I haven't replaced the fuel pump or the coils and it seems one coil was replaced and it was the one on the passenger side. And would 205/45/16 be too wide for my car?

 

245K is a lot of miles. have you done a compression test? You can also do a relative compression test, which measures the amount of effort it takes the battery/starter motor to turn each cylinder over on compression?

 

main sensors to be replaced when bad idilng in cavs are tps sensor , iac valve and map sensor, nothing more. and opening the torx screw a bit to open the throtle about. 0.5% no more,, the torx screw is a female screw,, kind of difficult to find, its a chevy measure i had to call a mechanic to borrow his tool. the torx is located in the throtle body underneath the plate that holds the accelerator cable,, you need a scan tool for this procedure, when the car stalls, two things are happening, y the iac in not getting the correct info from the tps sensor and it cant react fast enough and your car is choking.. check that th tps replacement is good, i had to buy two to get a good working one,, gm boxed spare parts are made in korea but they are decent enough. you can buy a basic thinkcar bluetooth scan tool, it will help you loads.. their very cheap. and will save you future headaches.

no 205 tires are too high for this car unless you elevate the chassis with reinforced springs,, if you use stock youll be hitting the chassis by bumping the tires everytime you take a turn or pothole, if you have fuel efficiency problem, not using recommended tires will not solve the problem, and forcing the drivetrain.