94 nissan sentra engine stalling - HELP!!?

I've got a 94 sentra with a 1.6L engine and Manual trans. about a month ago, it was jerking and surging and driving terribly (the engine has 199860 miles on it with a timing chain that was replaced at 163000). After it started acting up, i replaced the spark plugs, plug wires, distributor cap and rotor button, and the fuel filter. No change. I then replaced the Clutch (per suggestion from a mechanic who drove it). No change. I talked to a guy who suggested i try the Throttle Position Sensor. I couldn't get a TPS in for a day or so, so i made an adjustment on the one i had, which made the car drive worse than before...it was even stalling out when I'd hit the clutch at a stop light. So, now, after replacing the TPS, it's still no better. I'm desperate!!! What should I do???