Starting problems

1988 Toyota Corolla GTS, 169000 miles, 4A-GE engine: This car is very hard to start when it is cold and doesn't start at all when it warms up. I have replaced the spark plugs, spark plug wires, and the distributer cap and rotor. It cold started a little easier after I did that, but still will not start hot. I purchased an ohm-meter and checked the ignition coil. The secondary resistance is with-in range, but the primary is not. The specs for the primary resistance is 0.4-0.5 and the ignition coil barely gets down to 0.6, so I'm pretty sure that it needs replaced. I'm pretty sure that's not the only thing, however, because after I do get it started it tries to die again. Once it gets down to a about 800 RPM's, which is what it is supposed to be running at, it pretty much dies. It might be a vacuum leak, but I only found one cracked vacuum line, and that didn't fix it. When I rev the engine up it will sometimes stay between 2500 and 3500 RPM's until it fully warms up. After that it will stay running for the most part around 1100 RPM's, but again it will die if it gets below 800 RPM's. I'm hoping replacing the ignition coil will solve all my problems, but I figured I would check first. Thanks for your help.