Very slight "rubber band in drive train" sensation

Lately I have been noticing a very slight sensation when driving our 2007 like there is a rubber band in the drive train. The closest analogy I can make is what happens when a manual transmission car is left in 4th gear and the speed falls down to 15 mph or so and it starts bucking. But tone it down about 100x, so it is just a slight pulsing vibration and it lasts for no more than a second. It happens sometimes when accelerating from a full stop, and other times when the accelerator is pressed down following a coast to lower speeds (as in when timing arrival at a stop light). In both of these cases the ICE is starting up. I don't recall it ever happening when easing up on the pedal or maintaining even pressure. There are no odd noises.

My best guess is that something is very slightly off on the motor and what I'm feeling is the flex plate compensating. No CEL, and I have not yet checked for codes which would not set the light. If I plug in the mini-VCI cable and fire up Techstream, where should I look for evidence of a problem? Fuel trim? Anything else?

Or maybe a bad motor mount?

I'm not going to rule out the possibility that it always did this and I'm just obsessing about it now, so noticing it more.

Thanks.

 

It has been hot lately so the AC has been on most of the time. I will try to see if having the AC on or radio off increases that sensation. It could just be the ambient temperature is somehow involved. 102F air is not as dense as 70F air, and if the car isn't compensating correctly it might be lean or rich at the higher temperature. Maybe I should clean the MAF - isn't the air intake temperature sensor built into it?

 

Today the wife drove it while I ran Techstream. Of course I couldn't feel the problem vibration during that test. AC was on but it wasn't as hot as it was yesterday. Techstream showed rare single misfires, under "all", but with just 0 for the count in cylinders 1,2,3,4. Apparently 0+0+0+0 = 1! The corresponding RPM field was 0. By rare, I mean I saw it do it twice in ten minutes, and both times not ascribed to any cylinder. That field must be dynamic rather than cumulative, because after a while it resets to 0.

The target air fuel ratio was 0.999 and pretty much stayed there.

Atmospheric pressure read -0. Strange.

Scanned for codes and it only picked up the sun sensor, since the window screen was up at the time.

Drove the car by myself later and could only feel a very slight shudder when taking off from a stop, when the ICE kicked in. Couldn't feel the shudder when applying the accelerator when coasting.

So not super informative.

 

Yesterday cleaned the MAF sensor and the throttle body. The MAF was definitely dirty on one side of the bulb, so sprayed that until clean and shiny with CRC MAF Sensor Cleaner, also inside the body of the MAF. When that was mostly dry (still stinky, no visible fluid) put it back into the air cleaner box and then removed the air cleaner box. The throttle body wasn't very dirty on or above the flap. The hole where the air from the PCV valve comes out also wasn't very dirty. Just a few light streaks of black carbon on the aluminum walls and plate. Below the plate the aluminum walls were pretty black. Cleaned the aluminum walls as far down as I could reach and brass(?) plate with CRC Throttle Body and Air Intake Cleaner on strips of flannel pajama.

After the intake was back together took it for a drive and there was none of that rubber band feeling. Not a definitive test though because even though the AC was on it wasn't as hot as before, and heat seemed to make it worse. The car was always at least a little rough (some vibration) when the ICE came on, and I didn't feel that at all.

So, maybe that fixed it?