Another idle issues thread.

[Mr Blue]

Does sound like an idle switch problem. Engine off - move the throttle open by hand. Can you hear any clicks? Should be a click at the start of opening. Then a click with the throttle wide open.

I've had a few with the throttle closed idle switch not making contact. These are adjusted by Phillips head screws.

wires to the switch are also known to break. Right at the back of the inlet.

If that's all ok...I usually wave butane gas or carb cleaner around every vacume pipe. If the revs increase...there's the leak

Also inspect the rubber bung under the oil breather.

Everyone assumes its an isv issue. They rarely go wrong. If the revs bounce, the isv is trying to recover a stall

[Waspy]

Like I said, the switch clicks etc and multimetered the connection with no apparent issue

I'll give the carb cleaner trick a go (how does that work btw, sounds like witchcraft)

The bung seems okay. But if after I have changed all the vac lines it still persists, that will be replaced too.

[VW BUSH]

The carb cleaner gets drawn into the cylinders from the leaks in the vac pipes and affects ignition.
Be very careful with carb or other spray on liquids, they can catch fire on dodgy leads or hot manifolds and burn your garage down   Best use a butane torch.

[Mr Blue]

Ahh missed that part you mentioned.

[Waspy]

Right, vac lines (all the ones I could find) replaced. There may be more, I don't know. Anyway, started her up, reved her up quick a few times then let them drop. It caught them every time. But about 3 mins it it started doing it again. I'm running out of ideas. It is far less drivable like this, and it's tarnishing the driving pleasure somewhat. Also see attached image. What is the downward pipe, where does it go? It had a bit of rubber hose on it to start with, but when I touched it, it crumbled. So I replaced it temporarily with the hose in the pic. Still not great though.

[Santiago]

Image?

[Waspy]

Crap sorry

[Santiago]

Ah, that one.  Goes through the bulkhead to the back of your clocks module.  Allows the clocks to figure out your MFA mpg reading by them knowing engine load / manifold vacuum level.

Did you try disconnecting the TB connector yet, to see if anything changes?

[Waspy]

Ahh well, that has never worked (not that i need it).

Yeah, disconnected it and it rev'ed like crazy.

[Santiago]

OK, so you've proved that the idle switch is being 'seen' by the ECU, that's one thing ruled out.

I haven't seen you mention having checked or replaced the blue temperature sensor?