Micro switch ???
Discussion
Can anybody enlighten me by identifying the function of a micro switch on my S3. It is located on the alloy casting which is between the intake pipes and the plenum chamber. It is mounted by the throttle system in such a way that it operates as the throttle is closed. The reason for my question is that one of the two wires has become unsoldered and it doesn't seem to make any difference to anything whether I hold the wire on to make contact or leave it adrift. Any help appreciated.
Sounds like an idle switch. On most cars, when activated, it usually momentarily cuts of the fuel when you change gear, so the exhaust doesn't go pop. Also tells the ECU to adjust the idle valve (or play around with timing to get the idle speed on Motronic I).
On some of my Jetronic Alfas I found that disconnecting it left the revs a little higher during an upshift, making shifting a bit easier.
Hope this helps. - Jim
On some of my Jetronic Alfas I found that disconnecting it left the revs a little higher during an upshift, making shifting a bit easier.
Hope this helps. - Jim
Thanks for the suggestion Jim. I got the impression from looking at it that it could be a retro fit but then decided it wasn't as there are threads in the casting to mount it to. Have looked at various pictures posted on here but haven't seen another one yet. I am still waiting for my "Bible" Christmas present to see if it mentions it but latest estimate was Feb.
Thanks for the excellent quality photos Colin. They will definately come in handy as a point of comparison - I can see various differences already !! Unfortunately yours doesn't have the said micro switch and also there are no threads in your casting. I now wonder if it is a retro fit and somebody has drilled the casting ? I suppose the other alternative is the casting could be from another Ford.
Things have been tidied up somewhat since they were taken though... I'm sure somewhere in one of the manuals it mentions this, and I seem to think that it was the forerunner of the throttle pot on the cologne engine. All it did was to tell the ecu when the throttle was at idle, as Jim said. But I wouldn't expect to find it along with a throttle pot
. I wonder if it is the original throttle body?
. I wonder if it is the original throttle body?Thanks guys unfortunately I haven't got a digital camera to hand but may be able to organise one tomorrow. I will eventually try and do some continuity testing with a meter to try and trace the circuit but at the moment the twin core from the switch seems to disappear into a black hole. As I said at present it doesn't seem to do anything but sod's law says that if I tidy things up and remove it something will not work !!!
Sadly not Andy and besides it might upset the neighbours 
. However the plot thickens. As well as the two leads from the micro switch I also have a single wire from one side of the ignition coil which disappears into the bulkhead just by the makers plate with them. I am putting off going into the spaghetti under there until later !! I have also found a complicated engine wiring diagram in the service history which is part German part English but all it has is a phone number on the top which turns out to be a fax - probably the place it came from ? I may fax them tomorrow for some advice. All this because I decided to tidy up the engine bay. 
. However the plot thickens. As well as the two leads from the micro switch I also have a single wire from one side of the ignition coil which disappears into the bulkhead just by the makers plate with them. I am putting off going into the spaghetti under there until later !! I have also found a complicated engine wiring diagram in the service history which is part German part English but all it has is a phone number on the top which turns out to be a fax - probably the place it came from ? I may fax them tomorrow for some advice. All this because I decided to tidy up the engine bay. 
ratman said:
Thanks again Andy. I understand the concept but my next question is can it be wired into the existing ecu or have I possibly got a different ecu. I suppose the only way to tell is to disturb the spaghetti in the roof of the passenger footwell.
I've been down there,not a pretty sight
OK, a possible quick test to see if it is doing anything at all. Disconnect the throttlepot, open the throttle a bit (peg it open by hand to around a steady 2k), then depress the microswitch and see if the revs drop off at all. You could try shorting the wires too, just in case the switch itself is duff.
Of course it could be wired to a small amount of semtex under the drivers seat, so you may want to check there first
Andy
Of course it could be wired to a small amount of semtex under the drivers seat, so you may want to check there first
Andy
Gassing Station | S Series | Top of Page | What's New | My Stuff