Right Boxer dudes, first confusing problem in a while for me...
Sometimes (maybe 1 in 4 times) my car will play a weird idle game.
I start it up and it's normal for the first few seconds until I touch the accelerator pedal and drive off.
After that, when I drop back to idle again, the revs stay high (about 1700 or so).
After a few more minutes driving, the revs will not stay level. They drop from the 1700 to normal-ish, but they won't stay steady. It gets perilessly close to cutting out, but never quite manages it.
If I turn the engine off, wait a few seconds and start up again, everything goes back to normal.
It started doing it when a couple of my exhaust manifold gaskets were dodgy. I've fixed that now, but it still goes wonky every so often.
The accelerator cable tension is fine, which was an issue last year when the engine got very warm.
Could it be lambda related, idle control valve, or something else? But it doesn't do it all the time, which is what is confusing me.
The car is still very much driveable though, even when it's being funny.
It only seems to do it when i've started it from cold as well.