you can buy the valve secondhand from the junkyard - I believe that the corolla 2E valve also fits.. costs about 100 rs
Secondly - I wrote in another thread about the rpms dropping on headlamp and radiator fan operation. for clarity of my post in the engine pictures above you can see the carb with a lot of diaphragms -
The one with the little rubber boot is the dashpot - which makes the engine decelerate slower (holds throttle open for about half to one second when you leave the accelerator), The one hiding on the bottom slightly near the dashpot in front of the carb is the A/C idle up diaphragm (its connected to the vacuum solenoid on the firewall near the ignition coil). raises rpm when the A/C turns on
The diaphragm sitting nearly flush on top on the left side with a vacuum pipe and a slow valve is the chokebreaker. The big one beneath it is the secondary throttle opener and the one on the back of the carb is the one that raises rpms when you switch on your headlamps or whenever the radiator fans comes on without A/C - its connected to the solenoid beside the carb bolted to the engine mount