Louie7

I'm trying to get a handle on some acceleration issues and idle issues.
So, my '94 LS400 (with Trac) throws the code 47 (when reading Trac Codes, of course).
I'm told that code 47 means: When idle switch is ON, sub-throttle position sensor signal is 1.45V or higher

And that's where I'm confused. My understanding is that the sub-throttle position sensor, like the primary TPS should be seeing 5V from the ECU. But the code is telling me that the signal is 1.45V or higher. Does that mean the signal from the ECU is too low and should be higher? I haven't done any testing with a volt meter yet...I need a bit more clarity on what I'm shooting at. For instance, where is the 'idle switch, what turns it on or off and when?

Thanks... any comments appreciated. Louie7

helladrew

Try cleaning your throttle body.

Yes, the throttle body has a 5v reference from the ECU. But the description indicates a signal FROM the TPS, not to the TPS. So when you are off throttle @ a stop, the computer is seeing the throttle plate is open more than it should be @ idle.

Louie7

Thanks, helladrew..... sure that makes sense.

So, to be clear, when the code refers to 'Idle Switch'...I'm assuming there's an automatic switch that is activated 'ON' when I back off the accelerator?

helladrew

I don’t have the FSM in front of me but yes I️ believe so !

jbolt

did you figure it out?