I don't know why but the air metering plate on the K-Jetronic (280CE, 1978) has developed a bad flutter. Engine running poorly, then dying. There's a new WUR, new distributor, vacuum seals are good. But this fluttering is severe. Where do I start? Fuel pressure delivery or vacuum issues??

When fuel pressure is low it will do that.

__________________

90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff

Is your butterfly all clean ?

__________________
1985 300D 198K sold
1982 300D 202K
1989 300E 125K
1992 940T

"If you dont have time to do it safely, you dont have time to do it"

"The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."

Yes -- the butterfly is clean.

The fuel pressure is good from the tank.

Do you mean the secondary circuit pressure --from the WUR -- could be weak??

If you hooked a vacuum gauge to the intake manifold, you would get a similar flutter.

Have you tried to lightly push down / pull up on the plate? This would at least let you know if you are running rich / lean.

What is the history of this car? Were the parts changed in an attempt to fix the roughness?

Have you investigated the tank at all for the problem ,if never replaced after close to 40 yrs of service this maybe a good place to start.You can start by simple replacing the fuel filter ,cut open the old one after draining and soaking with water ,youll see what appears to be red brownish dirt ,rust .The answer is replacing with new ,replacing with a good reusable one ,or , cleaning then coating your original ,the cheapest route but has to be done correctly.I had to complete this procedure from tail to nose on a 190e , fuel system was nasty ,even succesfully had the fuel distibutor cleaned with a sonic cleaner ,she ran great.New plugs , injectors ,PUMP and filter wouldnt do it ,it had to be the tank with rust resisting the flow and it was in this case.After 4 months of weekend driving Im confident this car is reliable .