I'd just like to point out that your 900 does and Smitty's might have LH-Jet 2.4... and make for a bad comparison. I think it's a bit suspicious for a TPS to fail so early.

My thoughts: check your fuel injectors and AMM. The 3.1 TPS is not a switch in the way that all the previous ones are (one sto for idle, and one for WOT on the later ones). It's a throttle position sensor. So instead of two switches (for each extreme), it's a
potentiometer.

If your AMM and O2 sensor are okay, your TPS shouldn't adversely impact the mixture (you've still got a mechanical throttle after all).

However, shot vacuum hoses would surely let enough unmetered air in to create a rough idle and perhaps some pinging. If your car runs differently depending on the plugs, I'd wonder about how the rest of the ignition system is doing (cap, rotor, wires).

- alex