Hi all,


Got an 89 RS with 305TBI. When purchased the vacuum line that is meant to go from the intake to the thermostatic vacuum valve in the air cleaner, and then to on to the vacuum diaphragm motor at the end of the snorkel was not connected.

If you are unaware, the way this system works is that when intake air is cold, there is a flap in the snorkel that closes, and it draws hot air up the pipe that goes to the exhaust manifold. This is to increase intake air temp quickly for fuel atomization and to reduce choke time.

When I cold start this car, it sits at the 1500RPM choke speed for a substantial amount of time before finally coming down to normal once IAT organically rises. I went to go investigate the system today and found that my vacuum diaphragm motor and associated flap is being held open and the hole that would go down the stove pipe to the manifold, is plugged with a rubber cap that appears to also be holding the flap open. I have attached video for further review.

Can i just pull this out, and get the system back to proper working order?

 

 

Common on three-season cars. You really only need the heated-air intake when the weather is above BELOW ~50 degrees F. At ~40F and raining, throttle icing is a real possibility.

Some people need to have their fingers broken with their own wrenches.

Rip the plug out, verify the vacuum motor, reconnect all the vacuum hoses. Verify system operation.

But...late spring, summer, early fall, you may want to disable the vacuum motor.

 

Hi all

Just wanted to add some information incase anyone else sees this one day. It's also in the FSM above but to put it clearer on words:

The "plug" in my video, is supposed to be there. It's part of the flap and isn't a plug at all.

With no vacuum present (engine off or disconnected like it is in my video) the flap is OPEN by default and the "plug" blocks heat from the stove pipe.

In proper operation, once the engine is started the vacuum motor is snapped closed by manfiold vacuum which passes through a thermostatic vacuum valve inside the air cleaner. This is why the vacuum line connects to the base of the air cleaner and then continues on to the vacuum motor in the snorkel. Once IAT/MAT reaches 86 degrees it slowly starts to close, removing vacuum, allowing the flap to slowly open until it's fully open.

I tested the vacuum motor by hooking up a hand pump to it, and it works as designed. I have ordered 1/4" vacuum hose which will arrive tomorrow to hook it up and see if it works. Provided the thermostatic vacuum valve in the air cleaner still works than I presume it will.

Will update