1999 Ford Explorer

Shakes or Wobbles problem
1999 Ford Explorer 6 cyl Two Wheel Drive Automatic 135000 miles

My have check engine light on and the error code
P0171 and P0174 2 weeks ago. The SUV still run normal

Yesterday, it become shaking and lost and lost power then the check engine light blinking and smelling gas from exhaust smooke. Scan the code again. I got P0171 and P0174 and P0306

I brought to the shop they said MIGHT be the issue with intake manifold and they want $500. Is that reasonable? Any other possible cause the problem? What I should check?
February 4, 2010.

PO171 PO174 Lean bank 1& 2. Chances are you have a vacuum leak. It could be the intake, but check everything before ripping into the intake.