dryer still wont heat

Dryer still wont heat after replacing some parts.
4 months ago I replaced the ignitor with sucess, dryer has been working fine since then. A few days ago I noticed that clothes are taking forever to dry. What it does now: With all covers on, Ignitor glows orange flame will not ignite, dryer will keep trying to ignite every half minute or so. With the front cover off, ignitor will glow, flame will light but only burn for 30 seconds, shut off and repeat. I have been running these tests with the vent flue unhooked so that there is no chance of a blockage. Looked through all passages and there is a clear path for airflow.
Was told that is is not the flame sensor because the ignitor is coming on so I bought and installed new coils last night. Problem still exists. Ignitor glows, no flame, process repeats.
Is it possible that the flame sensor is bad? I now have a newer ignitor and new coil kit installed but no heat?

Thank you in advance.
Jeff

OK, I’m brave. I started the dryer, ignitor glowed orange, I reached in and pull a wire off the sensor and the flame ignited, burned for a few minutes and shut off.