The vehicle when it is cold will start and sometimes turn off. I have to let the engine warm up even though it is hot outside. I code for the knock sensor came up, but my mechanic is unsure if that will solve my problem. I have had a tune up, replaced distributor cap, pcv valve, wires, plugs, done an oil change, rotor cap was replaced, and all three belts have been replaced, also I had a leak in the cv boots and replaced the half shaft on the drivers side, with new brakes, rotors, and pads. I have rotated the tires, replaced the catylact converter in the back, and the muffler. There is a noise that is not a knocking and I wouldn't call it a tick but more like its chugging along. Also when I made too many turns the engine would shut off, but start right back up with no problem. There is no check engine light and recently the Air bag light has started to blink and will not shut off. The car would not turn on at one point, but after the tune up was done it started up fine and then the stalling and hesitation started again. Please help with any thoughts or ideas.