If power is good, I would not think it is a plugged exhaust. That is rare on a non-catalytic car. However, your symptoms seem like a flooded engine caused be small particles keeping the needle valve from fully closing. You may have some debris in your fuel tank and they are working there way up to the needle valve and while you are driving, you use up the leakage but when you come to an idle, if ooverfills the bowl and you flood the engine. That gives the exact symptoms you have. Do you have a good in-line filter installed? A quick fix that sometimes clears the problem temporarily, is to remove the fuel line, plug it, start the engine and let it run out of fuel. Then re-attach the fuel line and since the needle is all the way open, it may flush out that debris.