I feel your pain man
Windshield wiper doors and headlight vacuum problems are a PIA. While Ken has a good idea, I have yet to figure out how to search on the NCRS board........I may figure it out someday
. But, I will try to give you a couple of things to check. First, check the vacuum valve near the intake, it is an aluminum looking thing with three hoses connected to it, one hose is comming from the intake, one is going to the vacuum tank, and the other is going through the firewall. This valve is a one way only valve, it works a little like a diode, if we were talking about electricity. You should be able to blow through it in only one direction. Ok, let me try to explain why it works this way. The vacuum operated switches are operated bass akwards then you would think. The small hose on the relay is the "control", it has constant vacuum until the wiper door, or what ever is turned on. When vacuum is removed it allows the vacuum to flow through the switch therefore operating the device. A good example of this is, with the car running and the lights off, pull, or pinch off the small hose, blocking the vacuum. What happens?? The headlight comes up. Now, after all that, what is the valve for and what does it do. When you first start the car there is no vacuum is the tank. After the car runs for just a little bit the tank fills with vacuum, as long as there is vacuum, the headlights and wiper door will stay down. As you accelerate, vacuum drops, if the valve is bad, it allows the vauum to drop from the tank also therefore takeing vacuum away from the "control" hose, therefore allowing the wiper door or headlights to raise. Why, the wiper door first? Well, somtimes it is the headlights. It just depends on which has the least resistance, or which the vacuum is removed from first.........I hope this helps. I know that wiper door and headlights can be difficult to get to work correctly. This may not be the problem, but this is where I would look first........Steve