Lexus ES300 - stumbling engine - Ideas?

[turbo6bar]

My mom has a 2000 ES300 with over 210k miles. Recently, it began a terrible stumbling. It only happens after the car has warmed up. It happens in all gears, starts above idle, and continues until you get over just over 2000 rpm. It doesn't throw any codes. I sprayed propane around the intake and the engine didn't change pitch suggesting a vacuum leak.

Manually shifting the automatic transaxle does not eliminate the problem. I believe the problem is in the engine. I hooked up a scanner and noticed that it is cutting fuel when it's stumbling. Why would the ECU be cutting fuel?

I think it's a vacuum leak, but the fuel cut doesn't make sense. Wondering if it is doing this because it's going into closed loop operation. O2 sensors were replaced about 60k miles ago. I've heard injectors can be dirty, but it runs fine when I get on the throttle. If the engine starts stumbling, I can manually downshift, get to higher rpms and the stumbling ceases. It could also be masking the issue by reducing load. I noticed it is worst at slight throttle openings.

I have no problems taking it to a shop, but ego won't let this challenge go.

Ideas?

Thanks
Jurgen

[onewhippedpuppy]

No CEL? Lots of stuff can cause a stumble at idle and low RPM - coil packs, plugs, air filter, and fuel filter are all simple stuff. Start easy and work towards hard. When was the last comprehensive tune-up done?