Slightly rough idle when stopped [Archive] - Bimmerfest - BMW Forums

: Slightly rough idle when stopped

07-19-2012, 05:35 PM
So today at a stoplight, I noticed my car (just over 100k on the odo) was idling a bit rough. Throttle response is fine and no vibrations at any speed. RPM gauge looked steady around 600 RPMs or so when completely stopped.

When I got back today I parked my car and noticed the vibrations don't occur until after the car is completed stopped for several seconds. Opened the hood and there seemed to be a slight periodic hissing near the DISA valve.

This occurred about 1/2 way through a tank of fuel and I replaced the plugs about 5k miles ago so I'm ruling those out. Idrive doesn't say anything either.

I'm thinking its either the DISA valve or a leak in the hoses around it. Any thoughts? Is this something I need to have addressed ASAP or can it wait a week?

07-21-2012, 11:11 AM
Follow up for anyone else with the same symptoms - it was the DISA valve

07-22-2012, 01:30 PM
DISA can definitely cause you issues; when I replaced it on my e39, the flap-pin had lost it's retention rivet- it was literally SECONDS FROM DISASTER!


07-24-2012, 02:45 PM
SEEN THIS POST WAS UPDATED and wanted to add some helpful info for others here!

I had the same symptoms of rough Idle. I had the codes pulled on my vehicle and would highly suggest getting your codes pulled to help point you in a direction.
When I pulled mine, two codes pulled up:

1) PO171 &PO174 which both indicate the following possibilities which are; 1) MAF issue, 2) O2 Sensor(s) or least likely 3) Fuel pressure. Cleaning the MAF had no real effect and wasn't that dirty, but not entirely ruling it out that it may be bad.

Removed the MAF sensor and purchased some MAF cleaner and inspected, Not very dirty on the electrode or within it's housing, re-installed.

I Removed the DISA unit or better known as "Intake Runner Adjustable Unit" Or "Adjuster Unit", and found that the adjuster fin and pin were broken. I Purchased the part for $230, later while still looking into threads, I found this below which was a BIG HELP! There is a rebuild kit for this as a simple DIY for $75 and also has an upgraded full DISA unit for $299. I wish I would have known this before or I would have simply purchased the rebuild kit. However upon my inspection of my DISA unit, it was slightly damaged and was best it was entirely replaced.

(The Helpful Thread)

(Rebuild Source)