I've searched all the "fluttering" posts and found no conditions similar to mine.

The car: 1982 300 SD 117K original miles. It has been meticulously maintained in near original condition since new. Original owner family.

The conditions: Recently, only when accelerating, there is a brief fluttering noise from the passenger side of the front seat area. Even when laying upside down as somebody else drives, I can't tell if it is behind the glove box or in the kick panel area . The noise can't be replicated in the driveway through "power braking" or with the rear of the car on jackstands. I have also connected a Mity Vac to the vacuum line leading to the passenger compartment but can't recreate the noise that way either.

The HVAC system seems to be working correctly switching between MAX AC, defrost, heat, economy etc. As the fluttering is happening, I don't notice any vent positions changing but it may be too brief for that to happen. The fluttering occurs even when the HAVC system is completely shut down.

The vacuum system is set to at 11in HG at idle and drops to zero steadily when opening the throttle (plumbed a gauge in and drove it). Transmission shifts perfectly (just replaced K1/K2 for flaring). I dropped the vacuum settings as low as 8in HG but the fluttering persists. At 8in HG, the transmission would begin to get "bangy" when downshifting to a stop. I raised the system vacuum to 13in HG temporarily but the fluttering was still present.

Vacuum pump, check valve on pump and air filter mounts were replaced 3K miles ago when I installed the Noel Coulantes built engine. Long story on why it needed an engine so early in life but I'll bore you with that drama once we figure this out!

I know the vacuum door lock systems are separate but they held vacuum for a year while I was in Afghanistan. Just a potential indicator of overall condition to help paint the picture.

The car does have the correct fuel return line installed.

I'm at a loss for the cause of this most irritating noise aside from a failing vacuum motor or diaphragm device. However, if failing, why only a brief flutter and not all the time vacuum is applied? I don't mind tearing into the dash but would really like to tap some of the experiences and knowledge of the group first!

Thanks for the help!

Ended up being the drive shaft center support bushing. When I re-installed the engine/transmission, I obviously did not get the mounting relationships square. The noise would travel through the solid shift linkage and manifest itself inside the console area. Can't explain why on jack stands the noise was not apparent. Fixed....2,500 miles later, it's still enjoyable to drive again!

Thanks for sharing.

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1983 300SD Turbo

Some how this thread slipped by me in July. Good you figured it out, some times it is the littlest things that cause us to pull out the most hair.

I guess when you were up on Jack Stands, you didn`t get the flutter because the Drivetrain wasn`t under load, and was more or less free wheeling.

Sounds like you have a very nice SD, and should last you a long time especially with a new engine.

Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

I have learned a lot over the years, lurking out here -- many thanks to folks like you for taking the time to post your findings. -- Ch