2005 Sonata losing power during acceleration
 

No check engine light on. The engine will drop 1-2,000 RPMs while accelerating from a stop and while cruising (usually 45-55 mph, and around 3000 RPMs). The car will slow rapidly like it is trying to downshift and if the gas pedal stays pressed it gives no power or acceleration, but if I release the gas completely the engine recovers immediately. Any ideas?

how many miles?? when was the last time the plugs were changed?? fuel filter?? sounds like you are running out of fuel, or have a restriction in the exhaust. this could be related tothe cat, but without specifics, i cannot say for certain.

a fuel pressure check is in order, and if that is within specs (during the driving conditions in which is presents) then i would suggest removing the o2 sensor to allow the exhaust to be able to flow better while repeating the drive test.

again, check the basics of the plugs and filters first as these are intended to be replaced as part of the maintenance to the vehicle. if they need to be service, do so, then test drive to see if the condition still presents itself. if so, then proceed with the above mentioned diagnostic proceedures.

any questions, just let me know.

df