The upshift indicator on my '87 GTi started acting funny recently (started coming on at much higher RPM than usual). I removed, tested and reinstalled the vacuum switch that is in line with the vacuum hose from the throttle body to the fuel distributor. No problem found, but the upshift indicator now works. I do have a few questions, however:
- The upshift indicator does not come on when I remove my foot from the gas pedal, yet the wiring diagram shows no connection to a throttle position switch. How does the upshift indicator know the difference between no throttle and very little throttle? I speculate that perhaps ECU leaves the Idle Air control valve (or whatever it was called that year) wide open during fuel shut-off, thereby reducing the amount of manifold vacuum enough to turn of the upshift indicator.
- The wiring diagram shows that there is an "Upshift Solenoid Valve" that is connected to the same terminal of the upshift indicator control unit as the wire from the transmission switch. I assume that this is an input-only to the control unit, and that the solenoid valve therefore is operated by the tranny switch. This seems utterly bizarre, what does this solenoid valve control? Is this somehow related to the MFA?
I appreciate any help in shedding light on this!