Title pretty well describes the situation. I have 145K miles on the car, change oil regularly and do maintenance as needed (so far, not much).

Driving in town the car the car's acceleration is normal. And soon after entering the interstate the acceleration is pretty good. But I notice after I drive it for over 15 - 20 minutes (and most noticeably after 2-3 hrs) of driving in the 80 mph - 90 mph range if I punch it, the car feels like the engine is misfiring but I get no backfire. Flooring it actually retards acceleration while a slow push on the pedal to maintain constant acceleration seems to work.

I thought it might be something with the ignition but I don't understand why it would only be apparent at high speed -- which would seem to indicate a fuel flow problem maybe?

Ideas?

Thanks,

Botnst

PS I get about 25 mpg hwy and about 20 in town. Pretty darned consistently for 3 years.

The key words in your post are, "maintenance as needed so far not much"
There is normally more than a little maintenance required on these cars.

Here are some experienced based thoughts. Have you changed the fuel filter every 30,000 miles? Air filter on schedule? The sparkplug connectors? The sparkplugs? Then you get to the more expensive possibilities.

Mass AirFlow Sensor bad? Both M104 engine cars I have and currently own had this part replaced.

Wiring Harness? '93 to '95 had the harnesses that dis-integrate.

Search this forum or google search.

Steve

Ah, that's what I was hoping for. I have changed the fuel filter and air filter. But that was at just about 50K miles ago. In truth, I hadn't considered either but they are both really good possibilities. And both have the twin virtues of reasonable cause and modest expense. And the fuel filter should be changed, anyway.

I would have thought that the wiring harness would have pooped-out well before now. I have been praying that the P.O. had changed it but I don't know. But there are no spurious electrical issues ... yet ....

I don't know how to check the mass flow sensor. I had one go out on a Mitsubishi pickup. It's symptoms were: The truck died or the truck ran -- none of this pussy-footin' around with bad high-speed acceleration. New for the Mitey Max, the bloomin' thing was expensive so I pulled one at a wrecking yard and it worked okay. So how do you check the mass flow meter in a 95 E320?

I have changed neither the sparkplugs nor connectors. Would operating properly at moderate and low speed/low demand but failing at high speed/high demand be symptomatic of plugs & connectors?

Thanks for the suggestion that I search this forum. I tried a couple of ways but the symptoms I described weren't amenable to a definitive search. So I posted here in hopes of narrowing the possibilities, which you have done and for which you have my gratitude.

Bot

No, probably not. The issue you describe seems more likely to be fuel/mixture-related, rather than electrical, although a failing harness could be categorized as both, I suppose. MAF and harness are both suspect and should be ruled out before pursuing other avenues.

I had a problem similar to yours when I had my 1993 300E (3.2) "E320", and it was a bad coil wire.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

That harness is dear, yeah. Looks not too difficult to change, once you bought the dang thing.

I've been leaning toward the fuel thing since softconsult suggested the filter. One of those, "D'-OH!" moments.

Paul,
Last time I had a coil problem it turned-out to be a connector to the coil on a 1964 F-100. It idled okay but bogged under a strain. Hmmm. I'll check the connectors on the car.

Bot

Yeah, both suspect items I mentioned are priced way beyond an experiment, IMO. I'd seek a hands-on professional opinion before shelling out that kind of cash. Hopefully, it's something short, sweet, and simple instead. Good luck!

Good final advice from GS, especially to occasional greasemonkeys with limited diagnostic tools -- me.

Thanks to all of you. The suggestions are deeply appreciated.

Botnst