I have a 16 year old Maytag gas dryer that's taking forever to dry clothes. The initial burn lasts about 15 seconds or so. Every burn after that lasts 5-10 seconds. Minutes can pass without any burn going on.
Here's what I've done so far: made sure air vent was clear and replaced the gas valve coils. I also tested the rest of the heating components like the hi-limit thermostat, the operating thermostat(I think that's the one with the 5 terminals), the radiant sensor, and the igniter. The igniter was replaced a little over a year ago. I don't want to keep buying parts, but I'm to the point now where I'd rather try parts than to pay a repairman even more $$$. What next?

Yipes!! Can't be the ignitor.

It's something to do with the flame proving system. It can be that the thermocouple is dirty OR, and this one drove me nuts, the cobra shaped burner head.

After the dryer fires for a while and shuts down, try to bend the burner head. If it bends easily, replace it. It needs to deflect some of the main burner flame onto the flame sensor, otherwise the gas shuts off.