I've decided to take another crack at my oh-so-infamous E30 idle problems. A recap of the situation: When I got the car two years ago, it idled fine, with the stock ICV in place, plugged in. About 3/4 of a year after that, during the summer, my idle surged beyond belief into the 3000's. Unlike most peoples' idle problems, however, my idle stayed there; 3500RPM steady. This made it driving in town almost impossible and pretty much reduced the lifespan of my clutch. My brother came up with an ingenious solution. He mounted a plumbing valve inline to the ICV and regulated the idle speed with that. At the moment, the valve is set to a particular position and regulates the idle to 1000RPM. Why 1000? When cold, the engine will rev lower than that, say 650-700RPM. A strange problem has reared its ugly head when the idle would drop (when cold) a few hundred RPM and the engine would make a strange knocking noise. If I raised the RPM's to prevent it from doing that, it would still drop and make that knocking sound, even if it isn't near stalling speed. So, if I start the car (with the valve set to 750-800RPM when warm), it will stall almost immediately if I don't keep the revs up until the engine warms up. I'm not going to sit there and keep revs up while waiting for it to warm up. This knocking thing is a completely different issue and is irrelevant to my idle problems, which existed before the knocking started happening. So why bother with the idle problem if it's "sorted" with the valve set to 1000RPM? Well, I have to submit the car through emissions by March and the last time it was inspected, it was before my idle problem occurred in the first place. I'm afraid it won't pass emissions. Currently it's running rich, I'm guessing due to the high idle speed set by the plumbing valve. Also, winter is coming, and it will be harder to keep the revs up when cold starting, especially when I'm running to work and risk being late if I wait for it to warm up, so I have to drive in traffic, keeping the revs up 'till I reach the freeway, which is a major pain and stall multiple times in the process. Now, diagnostic steps taken: I replaced the stock valve that was in the car when purchased with a valve bought on eBay. It was a valve that was 20 years old, but brand new (never used). I figured for $20 or so, it couldn't hurt to give it a try. I put that bad boy in there and was fine for a few days. Then, the idle from hell returned, revving at an optimistic 3500RPM. I also tried another used valve bought from a parts store and that did it as well. Some say it's a vacuum leak, but if that is the case, then why doesn't the idle surge when the plumbing valve is in place? If it was a vacuum leak, then wouldn't it happen even with the plumbing valve in and the ICV disconnected? Currently I run with the ICV disconnected and the PV in place. With the PV set to fully open and the ICV in place, the idle from hell becomes apparent. When it doesn't idle 3500, it surges between idle and 1300 RPM, which is still unacceptable. So, my main question is; could it still be a vacuum leak if it doesn't affect idle with the PV in place and ICV disconnected?