My wife bought this convertible for a sunny day cruiser, and it's in very nice shape overall. Just 72k miles on it. Since we got it, it has idled very roughly on cold starts for about 10 to 15 seconds, after which it smooths right out and gets downright silky. I've already done new plugs and looked everything over. No CEL's. Drives great.
I've heard this is typical behavior as the VANOS system gets some miles on it. Should we drive it as is? How tough is the fix?
Thx!
hmm.... MAF? I dunno...
Common but not really a VANOS problem. It is a cold start programming thing. When everything is cold the EFI has to dump a lot of fuel and all the settings are changing rapidly for the first 2-3 minutes, most of it immediately after it fires. Every E36 and E46 has it to some extent - if it is more like its going to stall or its just making a lot of vibration/noise - at 72k I would check:
Pretty sure the AC is off, has fresh plugs & filters. I went over the air pump operation when the CEL came on, and ended up replacing the vacuum control switch to fix it. Everything else tested out fine.
It's most noticeable as a chuffing from the exhaust, not so much as vibration.
1988RedT2 wrote: Pretty sure the AC is off, has fresh plugs & filters. I went over the air pump operation when the CEL came on, and ended up replacing the vacuum control switch to fix it. Everything else tested out fine. It's most noticeable as a chuffing from the exhaust, not so much as vibration.
"Chuff" from the exhaust is because the air pump is working. It pumps air into the exhaust manifolds to help dilute the extra rich fuel mix needed for a cold start. It is only required until the internal heater in the cats themselves come up to temp. Usually less than a minute. If its hot out - it might not run at all so maybe you are just noticing it for the first time because its winter?
Giant Purple Snorklewacker wrote:1988RedT2 wrote: Pretty sure the AC is off, has fresh plugs & filters. I went over the air pump operation when the CEL came on, and ended up replacing the vacuum control switch to fix it. Everything else tested out fine. It's most noticeable as a chuffing from the exhaust, not so much as vibration."Chuff" from the exhaust is because the air pump is working. It pumps air into the exhaust manifolds to help dilute the extra rich fuel mix needed for a cold start. It is only required until the internal heater in the cats themselves come up to temp. Usually less than a minute. If its hot out - it might not run at all so maybe you are just noticing it for the first time because its winter?
Naw, it's pretty much done it since last Spring, and it's definitely running rough while it's doing it.
Sounds like you've got the first of the cold-start symptoms of VANOS seals going bad. The rough running will be followed by an oscillating idle until the car is warm and off-idle stumbling if the seals are allowed to go. Some M54s (the 3.0, mostly) also develop a rattle. BMW has developed a software "fix," but it apparently just reduces the sensitivity of the idle-control system to input from the VANOS sensors, masking the problem rather than resolving it.
There's been a lot of discussion about this issue, and as far as I know no one has been able to pin down the exact reason why VANOS seal degradation causes these cold-start problems, but I can tell you there are a lot of people who've had some form of the problem and resolved it by changing the seals, myself included. The performance benefits are a nice bonus, especially at low (<4000) RPM.
You've got a single VANOS, which means you need some special tools to complete the repair. Beyond that, it's about a four-hour job and pretty straight-forward. Seals are $60 or so from Beisan Systems. Good time to do all sorts of other maintenance while you're in there.
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