my car idles rough and or dies, but sometimes idles like a new car with no other changes in car. I found that if the the clutch pedal's switch is not engaged, ie. the clutch is slightly depressed, the idle is perfect no matter what. wtf does this switch do exactly? and why does it so greatly effect my idle?

 

Well, I believe the only purpose of that switch is to keep you from starting the car with the clutch engaged. ie: car in gear and starting.

 

does it effect the cold start system in some way?

 

No. Its an open close switch. Either it breaks the circuit for the starter so you can't start the car with it in gear, or when you press the clutch pedal down, it connects the circuit and allows the car to start.

 

there are 2 switches.

1. goes in the starter circuit, it makes you push the pedal to start the car

2. the second switch tells the ecu to turn on the idling system, if its not working the cruise control wont cancel either

 

S4's have two clutch switches- one for the starter circuit interlock, and one for the ECU "clutch engaged" signal input...It may be the latter one that you think is affecting your idle, because it actuates very early in peddle application, unlike the interlock switch...

 

IMO if you're having idle issues with clutch not engaged, its more about turbing the driveline than it is about the switch. I don't think the switch changes that much at idle.

 

disconnected the switch and jumped the connector with a paper clip and now zero idle issues. so? wtf is wrong with the switch?

 

THAT switch effects the idle mixture when the cars engine is cold. After the car starts up and is warm/hot it should not effect the idle.

The second switch on the clutch does effect the cruise contro. It will cause the cruise control to drop out when depressed, but is not needed for cruise control operation. Mine's been disconnected for years now. I use the brake pedal to disengage cruise prior to depressing the clutch.....to prevent over reving the engine.

What the fellow said about drive train issures makes sense .....but I went down that road til I found out...no....its the signal to the ECU from the switch that effects idle mixture that causes the change in idle.

 

yeah, for the longest time I thought it was my tranny because it is less than perfect. I think my car only idled fine if I started it after it was warmed up, so I'm thinking my ECU wasn't using the signal correctly, and after opening up my ecu and finding a couple burnt components I'm pretty sure that's it.