For my new-to-me 190D turbo, the engine has an odd surging to it. It's very similar to surging from a cruise control, but this happens without the cruise engaged or even attached. It seems to happen mostly at higher rpms.

It's like the engine cuts out and then cuts in again.

I'm wondering if the turbo is cutting out (but I'm totally ignorant of turbos--do they always operate or is there some control?). In doing some reading, I'm suspecting the overboost protection valve or the turbo waste gate, but I'm not clear if failures could be intermittent like on my engine.

Any thoughts? Suggestions? (Remember, I don't know much about turbo operations.)

I havn't had this problem with mine. If you can't find anything in the fuel system (filters), Air is what's left. What RPM do you notice the cut out.

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84 300D 251K
87 190DT 281K - Sold
06 Ford Escape 172K
94 Ford Ranger 250K
99 Chevy Suburban 181K

It's hard to get the problem to repeat on demand--it's somewhat irregular, but it generally occurs at higher rpms. I suspect something with the turbo because I think it happens only when the turbo is working.

From what I remember the turbo helps mostly on acceleration. Once the car's at speed the horsepower requirments drop. If this problem shows up on acceleration and your filters are clean then the turbo may be your culprit. Otherwise it may take a little more digging.

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84 300D 251K
87 190DT 281K - Sold
06 Ford Escape 172K
94 Ford Ranger 250K
99 Chevy Suburban 181K

I had the same problem, intermittent surging.

There are rubber fuel lines running from the tank outlet/return to the metal lines running forward. On my 85 300SD, one was weeping and there was air in the primary filter. I replaced the leaky hose and used a MityVac with a brake bleed attachment to purge all air from the line. I also replaced a leaky priming pump at the same time. I guess if fuel can get out, air can get in. Seal all possible air leaks and then purge any air from the spin-on filter. Those fixes worked for me. Good luck.

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1985 300SD, 203,000 miles, dark blue

Lil Sarah says: "Poor old Grandma Blue Car...She's sad."

Check the overboost protection circuit and the turbo's wastegate. If the wastegate ceases to function, the overboost protection circuit will remove boost from the ALDA, and you will lose power. Soon after fuel is cut, the boost drops below the 16 psi overboost limit, the protection circuit restores boost to the ALDA, power and boost increase, and the scenario repeats itself in this "surging" manner.

Symptoms of overboost protection include power surging when you're heavy on the Go Pedal and boost fluctuating between ~8 PSI and 16 PSI (this can be verified with a boost gauge).

Nice car! Good luck getting it working properly again.