Throttle Position Switch 308 QV Question

yes, there's a microswitch inside that is making the noise. You can also test the thing (assuming a certain contortionism if you don't dismount it) per below.

bosch part # 0 280 120 310 on the 328. Pretty sure it's the same on yours.
ebay price is $33.50 (including shipping) currently.

it's usually pretty cocked on the throttle body when positioned right.
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the leaf switch on the left in the above pic is the WOT switch. You can usually feel a small resistance when the cam operates the switch.

the microswitch on the right just closes when the throttle is closed. The adjust is to loosen the two bolts and rotate the thing counterclockwise until you hear/feel the microswitch click closed, then tighten the bolts at that position.

if the microswitch fails, it's usually cruddy contacts inside. It'll still do it's clicking thing, but the closed switch will be high/infinite resistance. That's why measuring it is really needed. If you happen to have the injection ecu plate up, then it easiest to check the throttle switch from there.

wrt what the throttle switch actually does, my memory is a bit vague. Both of the switches feed into the injection ecu. I assume the WOT one signals for fuel enrichment, and the throttle closed one may be for tweaking to prevent idle undershoot.

one of the switches can also power the relay that is controlling the electrovalve for the air injection cutoff valve. Whether it turns off the air injection, or turns it on I don't remember.

on the 328, the other switch also connects to the ignition ecu. May not connect to the digiplexes.

I think it's been said that a bad microswitch can effect idle. I've never seen details on what the injection ecu is doing, though, so can't say for sure. One of these years I'm going to get around to hooking up some test equipment to the 328 and trying to figure out how these bits interact. A scope on the frequency valve should do most of it, since that's the only control the injection ecu has. A wideband O2 sensor would be nice to for measuring the fuel mixture, but I don't currently have one of those.

 

the throttle switch on 'pulsed' systems sends the signal to the ECU to correct for over swing on vane of the L-jet systems. it also provides full enrichment based on obviously throttle position for WOT and idle transition much like a progression circuit from the carb days. this is all on 'pulsed' injectors where you can adjust the flow rate at the injector. it's basic operation is to sync the signals from the vane to the throttle for proper fuel distrabution, some of them also control coasting fuel cut-off and RPM limitation, much like the KE.

my guess is it operates in a similar manner but pre-dates the KE-jet.
OK grabbed my Bosch book, the KE3-jetronic is the first system to use these inputs and was used by Audi in 1987 on the 5000's. no mention of the TPS on the CIS prior to that and no mention of it in the WSM's I have. Bosch stipulates that it operates two separate control units, ignition and injection. so it would function much like the motronic and KE3 or CIS-E III Mercedes employed in 1988.

so bottom line it's an 'electrical' version of a carbs accelerator pump, clear as mud right?