2001 Blazer rough idle, Cylinder 2 misfire.

This would be a po302 code: Possible causes cylinder #2 misfire>.. - Faulty spark plug 2 - Clogged or faulty fuel injector 2 - Faulty ignition coil 2 - Fuel injector 2 harness is open or shorted - Fuel injector 2 circuit poor electrical connection - Ignition coil 2 harness is open or shorted - Ignition coil 2 circuit poor electrical connection - Insufficient cylinder 2 compression - Incorrect fuel pressure - Intake air leak Tech notes The P0302 code means that the cylinder 2 is misfiring or is randomly misfiring. Start by checking for intake leaks an if no leaks are found the next step is to replace the spark plugs on cylinder 2. If the problem persist more tests needs to be done to diagnose problem

The check engine light comes on and flashes when I go over 30 mph but when I slow back down under 30mph it goes off. Is this caused by the same cylinder misfire code

Well you picked up a miss fire code on #2, I would check compression. It is possible the light would go on / off, but when the check engine light comes on, it set a code in the memory of the computer. So check compression.

I'm waiting to get a computer tester. I checked for vacuum leaks by spraying ether around all vacuum lines and intake and the rpms didn't change. So would it be some kind of sensor or injector harness? I'm out of ideas

What size engine? If it is the 5.3L may be the coil for that cylinder or a leaky injector. Verify compression tho.

I have a Chevy 2003 trail blazer. It's in the shop as we speak. The mechanic that sold me the blazer said that the thermostat and condenser needed changed. Just thought I'd let someone know, because I also tried all of the things that people have spoken of. Distributer cap, spark plugs,wires. I thought injectors so forth. But mechanic said thermostat and condenser.