PaulW

Last week I plugged the vag-com in and through the engine module, could see the throttle position and idle switch.

After looking at how sensitive the switch is, and how little throttle you put on the A8 when driving 45 MPH (when it hunts on flat ground) or when you lift on the highway, it sure feels like it is always associated with that switch being in the "made" or "on" position.

Give it a little gas to open circuit the switch and it seems to go away. Keep your foot on the pedal just a tiny bit when lifting on the highway, the torque converter won't drop out.

I know Tozo adjusted the switch so it would stay open....and he reported no change.

However, there is a procedure to adjust the throttle cable, then to reset the idle switch.

I will have to try it.

And my camera died this weekend, so I probably won't have any pictures.....

Let's see if I can expense a new one!!!

:-)

ttuling

The TCM needs to know when you're coasting so it can start slipping the converter clutch. That's normal on a non-thumping car. Don't blame the switch for what goes bad after it closes.

Again, when you take your foot off the gas, it is _normal_ for the converter clutch to go from locked to regulating (partially locked). You can confirm this using VAG-COM on a non-thumping car.

Therefore, a dropout when you take your foot off the gas isn't a totally misplaced event -- instead it's too much of a good thing: the converter clutch unlocked too much. The thump is the correction.

Hunting could arise from the same mechanism: too much reaction when the TCM tries to increase or decrease the converter clutch slip.

Tom

PaulW

You're probably right, but it's worth looking into.

Cjshutts

Paul, if the TCM memory is erased, does the hunting go away until it learns again?

ttuling

then there doesn't seem much opportunity for switch adjustment to make a difference, right? I'm thinking in that case the throttle closes so quickly that it doesn't really matter if the switch engages a few degrees early or late.

Tom

PaulW

No

Cjshutts

on the throttle switch around idle it might be a good band aid for the problem.

I wonder if the converter lock/unlock/partial lock is dropping the line pressure enough to cause slipping on the 4/5 clutches, thus causing converter to unlock, then the cycle repeats.

At light throttle the line pressure is most susceptable to pressure drops due to lower pump speed. At least this was true in the turbo 400 in my Oldsmobile

PaulW

So until the torque converter drops out, and engine speed changes, it's at the same output pressure.

Cjshutts

When this flowrate is consumed it will drop the line pressure. The effect of this is less at higher RPMs.

Just something I was thinking about.

PaulW

Got it