Old Kenmore gas dryer model #87557120 (1986) normally takes about 8 seconds for the ignitor to glow hot enough for the gas to ignite. But just recently, and intermittently, the ignitor will stop glowing after 4 seconds, and the gas doesn't get a chance to ignite. And sometimes it will glow long enough to ignite, but after a while, the flame will automatically shut off, and the drum goes cold, but there is no gas smell. It's as if there is a faulty thermostat or sensor or coil in the burner that is prematurely shutting off the gas and ignitor. What particular part do you think could be failing and causing this behavior? Thanks!

Never mind, I found the answer while browsing another site. A failing valve coil will cause these exact symptoms.