Intake valve deposits is what it is, plus buildup on/in the injectors. What happens is, after the engine is nice and cold throughout, as it is when it sits overnight, you go to start it up and the car calls for a rich mixture. So lots of fuel is coming out of the injectors. Problem is all the carbon and blow-by gases over the years have built up on the intake valves. These deposits act like sponges, especially after several hours of not being in use. You go to start it up and it calls for a richer mixture, and the valves end up absorbing a lot of the fuel that the ECU is expecting the engine to burn. So it starts stumbling because it is not getting the metered fuel it is supposed to be getting. After a bit of running, the intake valve deposits will become saturated and not absorb any more and the car will run fine. That is, until the next time you let it sit for hours and give those deposits time to dry up again. The answer is BG44K. That stuff works. One can works for 20 gallons of fuel. If you have sticky injectors or suspect clogged injectors, you will feel it work minutes after putting it in. Brother's truck had a misfire for about a year on his truck, didn't do anything until he needed an inspection. I suspected a clogged injector, put a can of bg44k in and drove it. I tell you, it was just bogging along for miles. All of a sudden, it started to shimmy while driving. I thought his transmission was probably failing too, but the darn thing started becoming alive! It became so responsive and strong. Try it. If you don't feel it working, it is beyond something that can be fixed by putting something in the tank. I too, am a fan of MMO in the tank, but it has to be used all the time in order to be effective. Further, if you have lots of blow-by, you'll get lots of soot coming back into your intake through the pcv and caking onto the valves as well. Not so sure the oil catch can or the techron is effective enough in your case. Ebay or some local car dealerships have it, call around. goes for around $20 a can. You can try intake valve cleaner sprays, but they're not effective enough in my opinion because you have no direct access to the valves. On the other hand, the bg44k is constantly sprayed onto the valves throughout the use of the fuel in the tank, and you also get your injectors cleaned at the same time. works best on short trip driving, because it gives time for the sooty stuff to absorb it over and over again and break apart.