Okay here goes....Car has been running perfect in every way until one morning when I tried to start it. I turned the ignition and it cranked like it had no spark or compression. Just a smooth starter whirring sound then it started but sounded like it was running on 3 or less cyl. with a loud knocking sound that resembled a huge exhaust leak. I thought maybe a spark plug had worked its way out, hence the rough idle and sound that resembles a compression or exhaust leak.

trouble shot and found all plugs and coils in place a secure. Started car again and same poor running condtion existed. I gave it some throttle and after a few seconds of really loud knocking a missing I heard a thud like something was sucked closed and all of the poor runnnig symptoms magically disappeared. Idles perfect, knocking disappeared. Restarted multple times and all is well.

that was 2 weeks ago....today it happened again as a cold start (ran perfect upon shut down the day before only this time it took a lot of cranking again with what appeared like no combustion, then a spark here, a spark there, then it started, but again it sounded like i was stumbling on 3 or less cyl. then same thing happened sound of something shutting and everything was fine and perfect running resumed.
Could it be a stuck open EGR valve that finally becomes free after a minute of terrible running?