check engine light flashing goes constant then flashes
 

about a week ago my check engine light flashed for abuot thirty seconds then went constant went to autozone code was misfire cylinder #4 put in a can of stp gas treatment next day or 2 light went away a week has passed drove about 150 miles getting about 16.1 mpg in the city drove about 400 miles highway today got 21.6 mpg when i got back home sitting in the driveway the check engine light flashed for about 30 seconds went constant about 30 minutes later drove to autozone to read code misfire cylinder #4 drove about 2 miles pulled in to get a bite to eat went from constant to flashing for about 30 seconds turned it off ate got back in light still constant drove about 200 ft started flashing for 30 second then went constant . my question is if the check engine is on then starts flashing dows that mean its reporting an addition code
thanks

Dude this is weird my truck has been doing just about the same thing. At random times the check engine light will come on. just comes on doesnt flash. its for a misfire on cylinder #3. the truck runs fine.. i cleared the code the first time and the second time it cleared it self. i am a mechanic, and my co-worker has the top of the line scaning tools that havent been released yet. i cannot figure out why it is doing this. i just put bran new plugs on my truck. and like i said it runs like normal. the last time it came on was friday morning. i drove it to work ( about 2 miles from my house ) and it sat in the parking lot untill about 3:30 when i was leaving. i started my truck the check engine light was on, i go to throw it in reverse and the check engine light came off. has not been on since.

Flashing CEL means serious fault detected, a misfire can do that.
The flashing will come and go, it is trying to call your attention to it, some people ignore the CEL, so they make it flash for 30 seconds if it is important.

3.0l in early 2000's had a problem with the heads, more specifically the valve seats in the heads, a seat would come loose and cause a misfire, then reseat itself and run OK for a bit then repeat the misfire.

Doing a compression test on ALL cylinders would eliminate that as a possible cause.
Remove all spark plugs then test each cylinder, 170psi would be expected

A few "regular" things can cause cylinder specific misfires.
Bad spark plug or wire
Bad/dirty injector.
Intake gasket on #4 is leaking

Basic spark timing is set by the Crank Position(CKP) sensor, but the Cam Position Sensor(CPS) does the advanced timing for spark.
3.0l is notorious for wearing out CPS sensors, they should be changed every 80k miles
This would usually cause a random misfire

This is exactly what my truck (3.0) was doing when its CPS went bad. I put it off for a little while then it started jumping from the misfire , changed the cps and everything was fine.