Car loses power when turning corners and climbing hills. Problem currently doesn't occur when using premium gas, as suggested by our independent mechanic who was unable to diagnose the problem when it first occurred in 1998. Dealer service rep, who diagnosed the problem in November 2000, says that the material which Toyota used for the engine block in the supercharged Previas was too soft so the engine developed secondary and tertiary ridge rings which, as I understand it, cause the anti-knock sensor to cut power to the engine under certain circumstances. It is masked when using premium gas which burns hotter but he said that as the ridge rings become more pronounced, the premium will cease to compensate and we could lose all power abruptly. The dealer has replaced the engine block for other Previa S/C owners whose vehicles are still under warranty but refuses to replace ours since the warranty has expired.

- Vicksburg, MI, USA