Fixed my lumpy idle

[Si-M240i]

Spent a good time trying to identify why my idle had become irratric and lumpy. I removed my Riss Racing air intake and fitted the Stock Airbox with an ITG foam Filter and that made little difference at all.

I then went on to look at leaks in vacuum lines etc... nothing there either.

Next I looked at the Recriculating Diverter valves on my Riss Racing DDV pipe and the one at the back was not operating properly as it wouldn't "keep" vacuum and the piston crept back to the closed position at idle, so I had one open and one closed.

I striped it down and replaced the seals on the piston as that's where it was leaking and re-greased with silicone grease and reassembled it. After this is operated ok. I tested by removing the vacum line on it while the engine idled and quickly apply and remove to see if the valve operates open and shut which it did. I then turned the engine off and fitted a pipe and sucked on it and sealed the end of the pipe with my tongue for 10 seconds and when I removed the seal I could hear the valve snap shut. When I did the latter test before, it would close within 1 second.

My idle is as smooth as can be now, so if any of you get a lumpy idle and have replaced the stock DDV's, it may be worth checking them for correct operation.

I did notice a small score in the piston, so will keep an eye on the operation to check that the new seals keep tight, otherwise I will be requesting a replacement piston.

Now I have done all the work and removed my Riss Racing intake, I need to decide if I am going to refit it. The performance drop is noticable but I have a service coming up in about 6 weeks and that rear pipe on the Stock airbox is a pig to get back on. I have ordered a Streamline Helene Air filter to fit in the Box for the time being and have still got the Scoops fitted. I will be interested to see how this goes. I miss the pull from 5k RPM to 7k RPM the most. Without the RR intake the car does feel a little asthmatic at high revs.

Also, I am keen to get the BMW performance upgrade and will need the Stock appearance for that and hopt they are not too concerned by the DDV pipe and valves.

[red_stapler]

Can you take pics to show what you did. This sounds good and I may want to try this.

[Si-M240i]

Originally Posted by red_stapler

Can you take pics to show what you did. This sounds good and I may want to try this.

Are you running after market DDV's ?

You can test it while it is off the car too. Just suck on the vacuum line, use your finger to feel the piston raised, seal your tongue over the vacuum line and iff after 10 seconds the pistion is still raised, remove your finger and take your tongue off the vacumm pipe and you will hear the piston return to the sealed position.

If when you do this the piston returns before you remove your tongue, then the DV is not operating properly.

As I have it all back on the car, I do not want to dissassemble it all to take pics.