944/951guy

I have a 964 that when you start it up and have it run the oil pressure jumps around from 2-4 bar which makes the idle jump around. Or is it the idle making the oil pressure jump around.... I dont know.

Engine sounds fine, seems fine. Smoked a little but nothing out of the ordinary.

Im just woundering why it is jumping around and not idle smoothly???

tbennett017

IMHO, the oil pressure will change due to idle speed. Not the other way around.

Wachuko

Bad sender unit, bad connection, bad gauge would be the first things to check.

944/951guy

Your right. Have any idea what would cause the idle to jump around even when the car is warm/hot?

Duck

Make sure the Idle microswitch is being engaged. Mine was not and the idle was erratic.

944/951guy

Where is the microswitch? In the engine bay but where? by the throttle cable somewhere?

Crystal Cranks

You might want to clean your ISV. Here's a good thread.
+ 1 on the oil pressure will change due to idle speed. Not the other way around.

boxsey911

+1 on the bad sender. Mine used to jump around like crazy. Replaced it with an OE one and it's been rock solid at just above 1 bar at idle ever since.

Nb. I tried replacing it with new aftermarket senders at first. These were disasters. Still jumped about or didn't work at all. So go for an OE one straight away if you decide to change it.

p.s. I think your pressure gauge and idle both jumping around are not related to each other and you have two minor problems to attend to.