Car emissions testing is an expensive scam. Technically, the results of any individual car test are not reproduceable. The variation from one moment to the next is enormous. Whether your car passes or fails is almost a matter of luck. (It is not uncommon for visible polluters to pass the test with flying colors, even though the car behind them can barely see through their exhaust.)
Emissions testing has had almost no impact on air quality. The improvement these past few years has more to do with car manufacturers being required to build cleaner engines (70% less smog output in cars three years old or newer) than with emissions testing.
The United States Supreme Court in the Printz decision ruled that Congress does not have the authority to require things like emissions testing. They suggested the states challenge Congress' usurpation of Constitutional authority.
The Court added that Congress gets away with such regulation through the "spending clause" - essentially, because they offer money (e.g., highway funds) which comes with attached regulations. (Similar to the school voucher situation.)
However, since the state collects the money for Congress, which Congress then returns with strings, it seems clear that Pennsylvania simply ought to keep the money it collects, and let Congress keep its strings.
Tom Ridge voted for emissions testing when he was in Congress and is now implementing it as Governor.