Just returned from a 700 mile round trip in my 80 300d, car ran fine, except on the way back. On the highway going 70mph, when approaching a hill or having to give it more gas, it acted like it was not getting fuel or cutting out. Once I let off accelerator it was fine.

The car has new fuel filters less than 4K miles ago or back in August. Engine temp ranged from 90 to 100C, A/C on. 165K miles on the car, maintenance is up to date. I have noticed that the car seem to run rougher than normal with the A/C on and stopped in gear. I thought perhaps it was running low on fuel, sometimes I don't trust the fuel gauge. Filled it up with almost 12 gallons, but the problem continued. Is there a shutoff if the engine RPM get's top high? Any thoughts?
Thanks

Sounds like a Fuel Supply issue not giving you enough Fuel to accelerate.

Most common issue is plugged Filters or Fuel Tank Screen.

Something growing inside of the Fuel Tank or contaminated Fuel does not care when the Fuel Filter was last changed.

To see if it is the Fuel Tank screen you can swap the positions of the Fuel Inlet Hose with the Fue Oultlet Hose (the Cigar Hose) where they come off of the Fender Well.
You will need to have at least 1/2 a Tank of Fuel as the Tank Screen will be bypassed and the Fuel will be drawn from a higher position in the Fuel Tank (that also means you will run out of Fuel sooner).
If after the Hose positions are swapped you situation improves the Tank Screen is restricted or plugged.

Take a good look at the Plastic Primary Filter to see if there is black or gray colored particles in it. If so you likely have something growing in your Fuel Tank. Some people use Startron for Diesels that eats up the growth.
You may need to change Filter more than once until the problem is over or clean out your Tank.

Other issues could be Air leaking into the Fuel Supply System, the Fuel Supply/Lift Pump needing rebuilding or the Fuel Pressure Relief/Overflow Valve not holding the pressure.

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You should also clean out your fuel tank breather.

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It sounds exactly like clogged filters. If you're confident that the filters haven't clogged up since the last swap, try cleaning the tank vent under the car. You can also go for a good drive then remove the fuel cap. If you get a suction noise then the vent is clogged. If that doesn't help then I'd try swapping the supply and return lines in the engine bay. This will bypass the tank screen. If the symptoms go away with this then you know the tank screen is clogged. That means it's time to drain the tank, remove the screen and clean it.

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I experienced it before with a plugged tank screen. If it were a plugged tank screen then you would see a lot of air bubbles in the primary filter. There is a quick way or a proper way to fix it.

Quick way - blow compress air from the feed line back into the tank to unclog it. It will work until the next time.

R&R the tank screen or remove and clean.

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Thanks guys, I will take a look at the screen and go ahead and replace the filters. My tank screen was clogged back in September, but I ran several treatments of startron. I could only run down to 1/4 a tank, the startron seemed to fix this issue.

Not to hijack the thread, but what is the best way to clean the tank vent. After a 50 mile or so drive, I get a fairly strong sucking/vacuum noise if I remove the fuel cap.....

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1983 Mercedes 300D 376K (diesel commuter)

They usually just get clogged up with mud and road grim. I'd just climb under with a small screw driver and break off any build up. It's a little bell shaped rubber piece on the end of the hard vent line.

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