Gas valve not opening to run oven.

Purchased from local dealer. 2002. performed ok, til about a year ago. On par with others. The ignitor fires up, glows bright. LP Gas valve is on the threshold of opening, but needs a light tap to convince it. Now oven reaches temp (Ignitor on all the while), and shuts down. (Ignitor off). Time for more heat, and must repeat the above. No schematic, and not heard of ohm value on ignitor. Voltages on valve are the same with ignitor on, or and tap on valve to open to heat oven. I question the ignitor on all oven run time, or and latching mechanism for the gas valve. Talking to the purchase location, they claim Ignitor with no reserve. They must have a clue.???? Just by frequency of dealing with??? Therefore nothing fixed yet. i'am skeptical. With Holidays arriving, I'am under extreme pressure to work, or buy new.