My toyota tacoma keeps stalling. Took it to the shop,and they replaced the fuel pump,cam and crank sensors. They said it was fixed.I drove it around for about twenty miles Seemed to run well,then began to start stalling. I had a complete valve job done about 90000 miles.It was running great till this stalling problem.The mechanics seem baffled. It is a 2.4litre engine. Got any ideas.