Porsche Enthusiasts Club Forum

Whilst investigating my idle problems I found that my idle switch is working fine, but the full throttle part of the switch is not.

I am hoping I will be able to repair it as they seem a bit pricey for a couple of microswitches! But it got me thinking, on the 16v engines, what effect does it have when this switch closes? Does it change the fuelling or ignition timing? Does it make much difference at all?

I have felt at times that the car bogs a bit with full throttle, so could be related.

On a side note, does anyone know the spec for the 16v knock sensors? Mine read as open circuit, which, depending on the type of knock sensor, could be normal.

I posted a few weeks ago about knock sensors for an S2( reads something like" knock sensors reusable?"
The replies included some figures that may help you.
I am yet to investigate mine.

Whoops,something went wrong

Hi Andy, here is the knock sensor topic:

viewtopic.php?f=25&t=16741

There seems to be two types, one with a few megohms resistance, one much lower. I think I have a couple of spares kicking around, I will see what readings they give.

I may have a TPS switch lying around spare, I'll have a look at the weekend.

I pinched the one from my spare throttle body for my 8v as they use the same part but I think my replacement engine came with another throttle body.

The WOT or Wide Open Throttle switch is there to take the car out of part throttle mode and into full throttle mode.

In full throttle mode the car ignores the airflow meter and lambda sensor (if it has one) and runs off of the wide open throttle maps for ignition and fueling with set figures for each rpm stage.

The reasoning is that without the switch activated, you could be cruising and not wanting to accelerate like a banshee, such as almost full throttle, going up a hill, with a fully loaded car of people and luggage, so will be wanting fuel economy, so a switch is there to say you are at full throttle and therefore want to use full power is there..

The alternatives to the bosch engineers would be to just assume the throttle is wide open due to the resistance of a throttle position sensor, but that would have the side effect of in a fault with the switch or wiring the DME/ECU may in some fault modes assume the car is at full throttle all the time, which would result in a rich mixture which would melt a catalytic converter which can potentially cause a fire.

Your car should come alive once you have a decent switch on there

Thanks for that John - just wanted to be clear on how the DME reacted to it being made.

I tried to dismantle the TPS but the seal was very well glued and there was no way I was going to get it off without cracking or distorting the case seam, so I decided to cut the top off and then reseal once I had found the problem.


20140227_083251 by Hallsy01, on Flickr

Pretty basic inside, a standard Burgess microswitch on the right for the idle switch, and cam switch on the left for WOT. Trouble is, at this point I could see little wrong with the WOT switch, and metering it out, all was well.

So either I had not had my probes on the pins properly, or taking it apart fixed it (very unlikely, but there was a rogue piece of plastic in there that may have been blocking the WOT contacts). The wiring diagram from workshop manual didn't work, as it showed a diagram with the pins numbered 3 - 1 - 2 , with the idle contact across 1 & 2, and the WOT contact across 3 & 2. 2 was definitely the common, but the pin sequence was 1 - 2- 3 as you'd expect. I'm certain I tried every configuration across the switch anyway, just possible I didn't have my probes quite touching when I tested the WOT switch.

Oh well, gave it a clean up and resealed, adjusted the throttle stop as it was set such that it wasn't touching the throttle stop, and the plate was binding a little in the TB body. I set it such that it just touched the closed throttle plate and then wound in a futher 1/4 turn - that is what I had read online, whether that is correct or not, I can't be sure.

Amongst other issues I will hopefully have the car back together today, so will see if I have resolved my idle issues!!