Our 2010 Prius with 33000 miles has developed strange 'engine racing'. At low speeds around 20-30mph, (warm) engine will rev up for 10+ sec with no foot on brake or accelerator. Then engine warning light comes on. Toyota dealer says "lean code", cleaned MAF sensor, checked AF and O2 sensors - OK. But same behavior continues- engine warning light back on. Otherwise runs normal. Any ideas?
Take it to a different dealer. If the warning light is coming on, there has got to be something wrong.
Maybe a fuel filter problem causing it to be lean. A dirty air filter would choke it and cause a rich condition. You have had alot of rain there....maybe water has seeped into an underground tank and contaminated the fuel. I'm sure Toyota dealers are few and far between there in VT.
My first thought is you are reaching a maximum state of charge. In this situation, the engine will rev up to bleed off excess power yet there is no change in traveling speed. This is completely normal. Your situation may be different though as there is a warning light which wouldn't happen in the above scenario.
Is the a/c on? Has the vehicle been in an accident or more importantly, a flood? Is the cat converter ok? Has the car been correctly serviced and if so by who and is there proof?
Dealer mentioned this possibility and said add dry gas - I did and saw no impact. Others asked Who serviced? - Toyota dealer in Rutland VT. A/c not on Problem basically when car is coasting thanks for your help!
No accident No flood - been housed in garage Serviced on scheduled by Toyota dealer we have been going to for 6 years - 2005 prius and this 2010
A dirty AIR filter may cause a loss in performance, but, it can't cause a "rich condition" in a Prius. The MAF sensor will balance the ratio of gas to air flow.
You could try running a good fuel system cleaner, like Chevron's Techron or Seafoam, to reduce potential injector blockage. Did they tell you the code number you have, or just say "lean code?"
Re: unexplained engine racing/vacuum-switching-valve failure Dealer found problem after two frustrating weeks of confusing codes, and car finally shutting down only a few hundred yards from dealer. Problem was 1) Vacuum switching valve was stuck open 2) This appeared to to have loosened a vacuum line. Result was a range of lean code, evap codes, MAF code(PO101); PO440 (incorrect purge flow), PO445 (gross leak detected), and presumably the racing engine that I noticed. Thanks to those who made suggestions- hope this helps others!
