Project 46: Idle Issues

Project 46 is an on-going series that demonstrates common fixes and preventative maintenance tips, as performed on our own E46 330Ci. Click here to read our introduction to the series.

As we mentioned last week, one of the first things we noticed when we took the 330Ci home was the erratic idle. We initially replaced the mass airflow sensor which fixed the cruise control and made a noticable difference to the way the vehicle drove, but the idle remained unsettled. After last week’s blog post, we pulled the DISA valve out to inspect it. The DISA valve is one of the more common parts to fail on the E46, so it was no surprise to find the internal flap completely detached from its housing. More concerning was the locking bolt just sitting freely in the intake manifold. Had that bolt been sucked into the motor, it could have caused a catastrophic engine failure. Not an ideal scenario after a week of ownership.



While half the components were off, we also decided to take a look at another weak area on the E46: the crankcase ventilation system (also known as the oil separator system). In the few days since we took delivery, the car had developed an odd and inconsistent clanging noise from somewhere at the top of the motor, which we realised was related to a problematic CCV. We found that the dipstick hose was completely severed and the upper oil separator vent tube had developed a crack, causing a vacuum leak. With all the parts being very brittle, some of them snapped during removal. A good reason to replace all four hoses when doing the job. As well as all oil separator hoses, the crankcase ventilation valve and the DISA valve were all replaced with brand-new parts from Vaico. After removal, it was clear to see just how clogged the original crankcase valve was with oil sediment.

Once everything was back together, the vehicle was started and the idle settled into a familiar purr, without any sign of that horrendous clanging noise. With the DISA valve installed, the engine delivered noticeably more low-to-mid range torque, improving the drivability of the car considerably and fixing the idle issue once and for all.  

When replacing the DISA valve and the crankcase ventilation system, we also noticed that the left-hand engine mount had disintegrated (something that really should have been noticed when the roadworthy was done the week before). Both engine mounts were swapped with replacements from Febi-Bilstein, fixing a background vibration that had been felt at idle and on acceleration. It’s always best to replace all engine mounts at the same time.


As our hands were already greasy, we decided for peace-of-mind to put one of our popular Oil Change Kits through the motor. The kit includes a new oil filter from original equipment manufacturer Mann, and BMW Longlife-01 approved oil from Motul. The X-cess 5w40 motor oil is 100% synthetic, providing greater heat stability and resistance to oil burn. Although it’s not the cheapest oil on the market today, we consider it to be cheap insurance. It’s a good thing we decided to perform the oil service as the oil filter we removed from the motor was very dirty and had started to collapse in on itself.

This week also saw the interior get a bit of attention. The seats, although generally in good condition and not yet to the point of cracking, were still quite dirty and noticeably dry. After a going-over with Autoglym’s Leather Cleaner, some Autoglym Leather Care Balm was applied to the seats. The job provided some much-needed moisture, in-turn restoring some lustre back into the black leather, and also immediately reinstating a rich leather smell to the BMW’s interior. As well as extending the life of the seats, it made the cabin a much nicer place to be.


It’s worth mentioning that the 330Ci we purchased is actually in very good condition, with basic maintenance performed fairly regularly by past owners. The components we’ve replaced were exactly what we were expecting to need replacing as they are the most common parts to go on the E46. Now that these simple components have been replaced, they won’t have to be looked at for another decade.


New Mechanical Repairs:
Oil Change Kit - Motul X-cess 8100 - $147
DISA Valve 3.0 - $265
Engine Mounts - $160
Crankcase Pressure Regulator Valve (Oil Separator) - $55
Upper Oil Separator Vent Tube - $30
Crankcase Ventilation Hose - $25
Crankcase Ventilation Hose - $15
Oil Separator Return Pipe - $28
Total Cost of Repairs: $1059

New Non-Essentials:
Autoglym Leather Cleaner - $24
Autoglym Leather Care Balm - $26
Total Cost of Additions: $62

Total Cost To Date: $1121

Back to blog