My issue only happens after hours-long runs at highway speeds or in really hot weather.

Basically what happens is after coming off the highway to a stop I will coast in.

When I completely let off the accelerator the engine will die.

You can watch the tachometer bury itself to zero.

Occasionally it will immediately bounce back up to idle.

However, it will often just die and stay that way until you put it in neutral or park and start it.

After I start it back the idle still isn't that strong and will struggle for a few seconds.

I can't figure out what might cause this.

Would a failing torque convertor cause this?

If not, what do you think would cause this?

How old are your Primary and Secondary Fuel filters?

What about the Fuel Strainer in the tank ?

How your Lift Pump (On the side of the I.P.)?

__________________
'84 300SD sold
124.128

Does your ELR work? I think that's the correct term

The funny looking dial under the hood, near the master cylinder. It is black with white numbers.

4 is the "normal" setting. It is an electric control of the idle speed. Moving the dial should make a noticeable difference in idle speed.

If the setting is too low, or the unit is not working at all this could cause some stalling issues.

__________________
87' 300DT (Grey w/ red leather)
87' 300TDT (silver w/ palamino tex) SOLD

2012 VW JSW TDI (on tdiclub.com all the time "btcost")

Possible tank vacuum accumulation if tank breather hose is obstructed. Lift pump does not want to draw or overcome the vacuum enough to provide adequate fuel.

When the car quits removing the fuel cap to see if there is a large vacuum present should tell the story. One way or another.

Secondary (canister style) is no more than three months old.

I've never replaced the clear, plastic filter.

I also don't know about the screen in the tank.

I'll clean the strainer and replace the primary for sure.

Where exactly is the tank breather hose?

I'll go out and check this in the morning.

I didn't know it existed...

Totally sounds like an air leak due to blockage.

While cleaning blow your lines out with compressed air.

They make a clear fuel line that's braided. Summit sells it but a brewery supply sells the same thing.

I haven't done my Benz yet but I like to run it to diagnose leaks, you can see where it's pulling bubbles, and it's usually blocked before that.

I can only guess how the breather system works, but if it has a charcoal canister to collect evaporated fuel and return it to tank, throw it away. It's an epa thing but they really don't work.

Not sure on 87s. Find out if it is the issue first anyways.

Generally with a partially restricted vent line on the fuel tank. The longer you drive the more vacuum accumulates. A test by driving with a loose fuel cap or presence of excessive vacuum when you remove the fuel cap after a fair drive.

Also too much air getting into the fuel system can create this issue. I would not want to see the a lot of bubbles out the return line of the injection pump after the engine is really warmed up. There should be none present actually. Although if you do not experience this on say twenty five mile runs it makes me suspect air may not be the issue.

Vacuum in the tank will make it start pulling air. Any fuel problem usually results in air. With enough restriction it can suck it right through the copper crush washers on a banjo fitting.

If there wasn't air, there wouldn't be a problem.

I can confirm that there isn't a vacuum in the tank.

However, there is significant pressure coming out when I remove the cap.

Is that normal?

Not sure how you are getting pressure in the tank, normally the fuel is sucked out (rather strongly) by the lift pump, and then relieved either by the return fuel flow or the tank breather vent.

With greater than 1/2 tank of fuel, temporarily swap the two fuel lines under the hood where the rubber lines meet the metal lines. This helps determine if your tank screen is clogged.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Do you have any idea where the cubic, possibly metallic particulate could have come from?

Could I have corrosion in my tank and that may have clogged my tank strainer?

I've replaced the tank strainer before and it's a major &*(_^.

In fact, I still have one I bought for another car but the memory of the first one I did kept me from going through with it.

I will say that I don't get the acceleration that people claim this car should provide.

I'll do the line swap this weekend to see how things go.