Well this is the 3rd time this has happened. 04 Lariat 5.4L Triton engine. Go to start the engine and there is a puff of smoke out of the back of the hood, doesnt start, restart, starts fine. Idles low, dies if I don't keep the gas pedal applied. Have to use the break and light gas when stopping. All my mech said was it was a vacuum seal. It is the middle of 3 seals and it keeps blowing out. Any ideas? I can not find anyone else here with this issue.. I have searched..

 

Find a new mechanic. The seals on the intake manifold? Either the mechanic isn't cleaning the mating surfaces well before the new gaskets or the parts are warped.

 

Good news is it was just a $38 vacuum harness. Replaced the right side vacuum harness by the injector rail..