Getting the VSS signal to the ECM
It must be emphasized that the VSS is used to control the idle speed when the vehicle is moving. Without the VSS, a vehicle may have stalling problems under certain conditions. Without a VSS, the engine computer (ECM) will not get the correct signals to run the engine for best fuel mileage. There are a lot of programs in the ECM that depend on the VSS. For best operation, the VSS needs to be connected and functioning.
In the Fiero wiring harness (I am speeking for manual transmision) the VSS signal is sent to the instrument cluster by way of C203 connector that sits just below the ECM. Here is an easy way to do this without hacking the wiring harness.
I am using Ed Parks' harness so I am missing the B9 and B10 wires in the connector that goes to the ECM. It is the center connector (24 pin) on the ECM. For those of you that made your own wiring harness the wires are present for you. So I had to add a wire for the VSS HI (B-10) and VSS LOW (B-9) signal. In Ed Parks' harness the blue clip can be easily removed. You will need two wires with the correct ends (thanks to Cplensdorf for giving me some) and slide them into the connector and replace the clip. Plug the connector back into the ECM.
To make this easier to show I had a spare C-203 and will do this next part on the work bench. The two wires that we are going to get the VSS signal from is the Yellow (C-203 pin G) and the Purple (C-203 pin R).
Unplug the black connector and raise the back on the clear connector. Use a very small piece of metal or a screwdriver to release the tab and pull the connector out.
With the connector out I soldered the wire from a two pin connector I picked up at Radio Shack. Remember what side is VSS Hi and VSS Low.
Last I connected the other end of the connecter to the VSS HI and VSS Low coming from the ECM. You will need 2 connectors that will slide into the ECM connector.
The end results is that when you are decelerating (down shifting) and then push the clutch in the RPMs will drop to 1250 and stay there until you get below 5 MPH (that it never saw with no VSS signal) and then it will go to your idle speed. Also I think the car runs better under acceleration. Here is a drawing, hope this has helped.
