E30 Zone

The car is a manual. When I first start it, the revs fluctuate up and down a bit then it settles. After this when you take it out of gear to slow down the revs will drop as normal but then drop to about 400, then it catches itself, shoots up to 2k rpm then settles at idle again.

I replaced the air flow meter with another used one but this didnt effect the problem. Also the classic temporary fix of resetting the ECU by disconnection the battery doesnt seem to effect it either.

Anyone had this problem or got any ideas?

First off you need to check for an air leak, check every where round the whole inlet side. Every gasket and peice of rubber,

Indeed sounds like an air leak or faulty ICV.

I had a nightmare with airleaks on my conversion when I first got it running, good thing is the gaskets and hoses are all still available from BMW for not too much money. The slightest split on the hoses messes up the idle, so have a good check over everything like zaust said

There are rubber blanks at the bottom of the manifold and they often look good but are the culprits.
Also the rocker cover to breather is often over looked.

Awesome, thanks for the help guys, will spray some carb cleaner around and see if I can find any leaks