my Goodman GMS9 furnace starts up and runs for a short time and then trips. There no codes. If I turn off the main breaker and turn it back on it starts again and then in a short time trips again. If I leave the door off of the section where the circuit board and blower and wiring are, the unit runs normally. If I put the door back on it trips again.

Symptom: The furnace turns on and runs normally for approximately 10 minutes at which time the gas valve begins to cycle off and on. The burners will go out but then immediately re-ignite then go out again. The furnace will continue to run but due to the cycling it will never heat the house to the target temperature and will just keep running. The unit is a Carrier 58DRC and is 30 years old. It has a pilot light with ignitor and two limit switches (overheat and flame roll-out with reset) it has no flame sensor probe. I replaced the filters and then tried a temporary bypass jumper of both limit switches but it does the same thing. One thing I have noticed is that when the gas valve turns on rather than making a clunk sound when the solenoid engages it makes a sort of chatter noise as if it's weak or undecided. It also makes this noise when it's doing the short cycle on/off symptom. So could be bad gas valve but not sure how to test that. Any tips or ideas? Thanks Paul