'94 Runs Well But Buzzy In Cold Temps.

[hdtrc]

94 olla runs smooth as butter in temps above 60 F. I mean reeeaaal smooth. Revs like a bat out of hell. When the weather turns cooler, the engine starts to buzz the entire car. If the weather is cool in the morning, the car buzzes. If the weather warms up during the day, it smoothes out. When the weather cools off at night, back to buzzin'. This can happen in one day. I have driven through cold fronts while on the highway and noticed the engine start to buzz and then smooth out after passing through the cold front. I am perplexed. New wires, cap, plugs, rotor, air filter, and thermostat all OEM Toyota parts...valves adjusted, FI cleaner, motor mounts, timing belt, water pump,brand of fuel, grade of fuel, etc.,etc., all made no difference over the past 30,000 miles. Anybody looking for a '94?