Engine Surging

My '86 528e has been running perfectly for 7 years until a few months ago. I turned it on and it revved itself to 4000rpm (straight 6... it tops out at 5k). After a while it levels back to normal idle rpms but it surges up to 2500rpm. When driving it, it automatically accelerates itself to these rpms.
I checked a bunch of the hoses but stopped once I started contorting my body. I tried to unplug the cold start plug last night but it didn't make a difference.
What is going on!!

Most likely it either has a bad icm which is the green box next to the ecu or the icv. You can try cleaning the icv out with wd40. Take it off and spray it with wd40 until it runs out clean.. with both I have good ones. 15 for the icv and 25 for the icm. Plus shipping.

Andy

Thanks, I'll try that!