One of three things is wrong:

1. You have a plugged filter. Have you replaced the the canister filter (the big one) lately?

2. You have an air leak. This seems to be the most likely as an ir leak will be hell on your top speed. Check ALL of your hose clamps and replace any and all fuel-line that came with your car as it is very likely shot.

3. Your injection pump is shot. Not likely.

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'84 190d 2.2 - Silver
Converted to 5-Speed
'84 190d 2.2 - Blue
Factory 5-Speed

'76 300D (W115)
Sold, found again in less auspicious circumstances