09' Altima weird idle/stall situation for all you gurus

[jwerty1]

Don't tell me to just take it to the shop and have nissan fix it, it should be under warranty. I am the Nissan tech.... Had the last 09 on the lot sold on wednesday, came in today with 95 miles, stalling and missing like crazy. Pulled codes, got p0300 (gee thanks), and a p0011 int valve timing, both current codes. Ok lets spray some carb clean around the intake, nothing, double check the exhaust, nothing. Data monitor, nothing abnormal other than the missing, a/f sensor reading ok, ignition timing w/in specs, running rich, so I'm led to believe that its definently not an intake leak, probably electrical or ignition component related, or worse, compression. Power balance test every cylinder produced very similar results, compression test #1 180, #2 165, #3 170, #4 155. Hmm, slightly out of spec in variation, but it should only be on cylinder 4, and I wouldn't suspect that kind of compression number to make it miss like it is. So I cleared the codes, and double checked the main grounds. Wanted to swap plugs and coils, but with it being an 09, we didn't have any parts, or any on the lot. So I think, I'll run it for a while and work on other stuff. I come back 1/2 hour or so later, it's purring like a kitten(keep in mind it was missing something fierce all morning). So I take it on a 10 mile ride and it seems great. Run it some more in the shop. And the salesman who sold the car said we had a used 09 on the lot, so I brought it in and the ecm numbers were the same, so I swapped them. Hoping that the used car would then run like crap, no, they both now run fine. So we kept the customers car over the weekend because I didn't want it to stall on him again and wasn't confident it was fixed. Well I drove it 60 or so miles today, cold, hot, warm. Ran great, no problems. How do I explain all this when I didn't fix anything? HELP