[dwells]

My '07 335i is having a whole host of problems. Namely:

• Stuttering/lurching under acceleration. Happens on light and moderate acceleration especially.
• Extremely poor gas mileage. Coldness seems to exacerbate the issue - I'm getting about 11mpg in city driving for my commute. I get around 18mpg in the summer on the same drive.
• Howling noise from the turbos. This is the third set of turbos, they were last replaced last summer under the extended eight year warranty which has now run up for me.
• Fluttering idle at start-up.

All of this has been going on for some time now and somehow has thrown no error codes whatsoever despite it all. So I'm not really sure how to troubleshoot it. Hopefully I can get some suggestions.

The car has 80,000 miles on it and I've maintained it well the whole time - oil changes at double frequency, filters changed, walnut blasting done, various repairs done at BMW specialty shops, etc.

Really not sure what to do here.

[Antetokounmpo]

Have you checked the injectors?

[thkfast]

I was going to suggest it's one of your turbos, but that wouldn't kill your MPG like you're saying...hmmmmm.

[Cory S]

3rd set of turbo's..... WTF.... What's killing them?

[sk55]

Boost leak?

[dwells]

Originally Posted by Heel Toe

Have you checked the injectors?

I'd thought of that, but you'd think I'd be getting codes or logged misfires if that were the case, right? If they weren't so damn expensive and require coding I'd replace them, but with how hard these damn cars depreciated, I can't justify tossing a few grand into it as a "guess and check" measure.

Originally Posted by Cory S

3rd set of turbo's..... WTF.... What's killing them?

Shoddy BMW workmanship. First set developed god-awful wastegate rattle and wouldn't hold boost, second set had rattle fresh out of the shop. The car was bone stock back then, too.

Originally Posted by sk55

Boost leak?

Yeah, I thought about that too. Looked over all the vacuum lines and connections and they all looked good. I've been running the JB4 with boost target on the gauges and it looks fine.

I've also tried resetting all adaptations and disabling the JB4, but neither had any impact.

[Nihil]

I'm new to BMW and this forum...not familiar at all with BMW yet. It says I have to post and wait an hour before my account is upgraded to full fledged account, so I'm attempting this now. Take my words with a grain of salt, as I'm only just becoming familiar with BMW.

As stated, not familiar with BMW, I have owned and am active with the 3/S community. (Mitsu 3000gt/Dodge Stealth) They're twin turbo. From your symptoms/description, it sounds like waste gates are a problematic part on the 335's. Now, on the 3/S's they've got a boost control solenoid, which is tied into the w/g actuators. Wondering if BMW has something similar, that could be causing issues for you, creating some surging issues, which would also wreak havoc on your turbos as well, also the BOV, perhaps? I read a lot of surging issues when people upgrade turbos and BOV's and have everything setup improperly, creating surging issues...though your symptoms are at idle as well, but BMW has a lot of neat gadgets that are electronically controlled, so I'm not sure if wonky things can be happening at idle because of faulty electronics.

Is there a way to possibly bypass any of the boost control system, enabling you to run w/g pressure, to see if the problem is eliminated?

(I've noticed different platforms have different nomenclature for parts so just to clarify, w/g=wastegate, BOV=blow off valve/bypass valve/diverter valve)

[smallseafishie]

Do you have any engine code errors?

[dwells]

Originally Posted by smallseafishie

Do you have any engine code errors?

I've done a few code reads through the JB4 - absolutely nothing comes up.

[smallseafishie]

Originally Posted by dwells

I've done a few code reads through the JB4 - absolutely nothing comes up.

What about historical codes with INPA?

[robthewrench]

A guess - bad engine temperature sensor. This would account for a lot of the factors with the exception of the noise from the turbos. The ECU may be sending too much fuel because it does not know the engine has warmed up.