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Weird flutter in my engine - what could this be?

2007 Chevy Suburban, 65K miles
Let me start by saying I took this into to the dealer and they found nothing!

When I accelerate, I get a “flutter” in the engine. The best description of this flutter is that the RPMs go down about 200 or 300. I think it feels like it is sluggish when it accelerates. It is most obvious during the 35 - 60 MPH range, but you also see it when cruising at 70 MPH.

I tried adding some fuel treatment and ran some 93 octane through it to see if it was the fuel injectors, with no change in the behavior. No error messages or engine light is on. Regular oil changes and services (60K service, every 3K miles for oil change). Driving behavior has changed since I bought a Prius 3 months ago. It used to be driven 40 miles / day (+ long trips) and now is driven about 40 miles / week (+ long trips).


The things that tell the ECU that the engine’s demands have changed when you floor the pedal, tellling it to increase the injector pulsewidths, are
the throttle position sensor
the mass airflow sensor (MAF)
and the manifold absolute pressure sensor.
the upstream oxygen sensor(s) monitor the output and provide a final tweak

While any of these malfunctioning should trip a failure code and a Check Engine Light, the signals should be looked at on an oscilloscope or using a meter under dynamic conditions (while the accelerator pedal is being pushed).

Feeding the injectors is the job of the fuel pump, controlled by the fuel pressure regulator. Fuel line pressure can and should be checked.

Then there’s the ability to breath out. Your exhaust system could be plugged by a collapsed ceramic substrate in the cat converter, or even a collapsed baffle in the muffler. The ability of the system to pass exhaust can also be checked.

Try a private shop. The dealership lacks the interest.

My wild guess is that you’re probably starving for fuel due to a weak fuel pump. How’s that for a hypocrit…first I tell you all this analysis should be done and then I make a wild guess!