My son is having an issue with a 2007 Toyota Yaris manual he bought second-hand recently. A week after taking possession he drove for about 15 minutes when he was caught for some time in a stationary traffic jam. The car started idling rough, then when he put it in gear the engine shuddered violently and had very little momentum. It was towed to a mechanic who replaced the fuel pump and spark plugs. But it is still occurring when the car is stationary in traffic for long periods. The fuel has been tested and was considered fine.