My xfire (2006, 11,000 miles) is garaged during the winter. About every 7-10 days I start it and run until it gets warm. If the weather is ok I drive it--very seldom this last winter. Recently the "check engine light" is on. The dealer said he thought it was bad gas. They checked all the possibilites and it was ok. Now every time I stop on an incline the car nearly stalls and I get the check engine light--suggestions?????