When i start up my 850, it has this 'surging' idle.. Ie up to 2000rpms, and back down to almost a stall if its cold enough. It does this up and down repeatedly. Could this be my 02's? Or my cats needing replacement?

Does it only do this when cold? Does it start resonably well when hot? If so, intake manifold gaskets are leaking. Get a smoke test done.

I agree with Wuffer, sounds to me like Intake Manifold gaskets.

Intake Manifold Gaskets. Do NOT reuse the old ones (experience talking here - unless you want to do the job twice!)

Here are some instructions from a fellow called AJ

"Check for vaccuum loss. When you car is idling remove the oil dipstick. If you hear a change in note then thats good. No change in note and no difference in RPM could mean that you have a vaccuum leak. Check vaccuum hoses and could mean PCV valves/check control valves."

Hope this helps

Also if this happens after engine is warmed up...might have something to do with DK units or........there are plugs in back of the Intake Manifold inside the water bypass that might be bad.
Hope this helps,
P. Ford

Yes, great advice...

Check for a vacuum leak with dipstick test and then with a smoke machine (the only way to find tiny cracks or holes in plastic or rubber hoses, etc). For sure clean out your DK Motors also. Replace Intake Manifold gasket with a fresh new one. Change PCV valve.

Let us know how it turns out.

Cheers

Yes, it only happens when it is cold, and is more severe the colder it is. When its warm, there is only the slightest variation in rpm, ie possibly normal variation. Thanks tons for all the advice guys! Can i do the smoke test on my own or do i need a mechanic with a smoke machine to do this? Also im not terribly familiar with the DK motors, is there a link for how to clean the motors/ what they are? I know they are related to the throttle bodies, but thats about it.

www.e31faq.com (http://www.e31faq.com) has a wealth of info (including DK motors).

Jim at e31parts.com also has them as refurbed units with warranty

perfect it explains lots!

I went down this road before Your best bet is $50 and a smoke test
the only to trully way tell if you have a leak 100% for sure small or large,
your DKs could be sticky when cold
I had the same problem DKS did not cure it no vacum leaks
do you have stock chips,
My problem turned out to be a bad mass air sensor when it was cold it would not function properly get the smoke test first, if that good i will see is i have an extra set of mafs i could lend you

Jim

Hi Jim, ya i have the stock chips in it. I think i will go ahead and get the smoke test done first, and if that doesnt work ill try to clean the dk's since that shouldnt do any harm. If that doesnt work i will contact you about those mafs. Thanks for the advice and the offer on the parts.
Braden

That Smoke test will take on issues of the table
proabbly the most expensive and time comsuimoing one to do
call on me anytime
Jim

Hey Jim, did u get my email?

I definately will if i need some help, thanks jim. I wont be doing it for a few months yet because its in storage for winter. So ill post something again or email you if i need some help.