bustermaxa

2000 ES 300 16500 miles just bought it.. engine stumbles (misfire) at mid throttle or on freeway... Idle just fine cold or warmed... here is the odd part... cold start runs great any throttle position any speed as soon as warm up starts to stumble (misfire) pull over and shut down and restart works great for 30 seconds and then starts to stumble? new coils, plugs, o2 sensors, a very well kept vehicle.. i am out of ideas??? no codes on dash board , no check engine light? i need help...
could it be the ECM?

Oro

I had this issue once on a vehicle and it was plugs. The core would heat enough to gap. Was it going on before the plug change, or start after? Defective plugs do happen. Another possibility is OCV valves. If the misfire is the whole engine stumbling and not one cylinder (unclear on that point), you have to look for a single source that can throw one or both banks off. One candidate is the OCV valves and when I had an issue with one bank, it could be described as you did, and it took a while to throw a code.