Hi Scotty, I have an 04 Tacoma, 3.4 liter, 280,000 miles, automatic transmission. The Check Engine light came on and it started running rough when cold. Coded as a P0171. Removed the MAS and cleaned it but it did not appear dirty to start with. There are no readily visible vacuum leaks. I changed the front O2 sensor last fall so I replaced the fuel filter. When I reconnected the battery, it ran worse - so rough it wouldn't pull itself onto the ramps. (I double checked the filter to make sure it wasn't in backwards, LOL). I forced air into the gas tank through a clean rag and it ran right so I changed the fuel pump. No difference. There is very little exhaust pressure at the tail pipe so we ran a pressure test and the Cats and Muffler are not stopped up.
I changed the PCV and cleaned the throttle body and oddly, after that it does run better for about 5 seconds right after it's cranked, then returns to running rough. Someone suggested EGR valve but I can't find it. This is not a CA model... and someone said it won't have an EGR valve but I dunno... Is there anything obvious that I'm missing or should I take it to a real mechanic? {black}:razz:
I would clean your idle air control valve if you have not.
It is not my first thing I would think of with your symptoms, I noticed it in my 4Runner with the 3.4 after getting hot and coming to a stop, it would bog down and sound like it was about to stop.
Wouldn't hurt to run some good fuel system treatment through it, like Royal Purple Max Clean, or the stuff Scotty talks about from the guys in arizona.
Thanks, nlord. I'll try that.