It can be many things: dirty air filter, dirty throttle body, bad spark plugs, injectors, fuel pump, old fuel filter, o2 sensor, mass air flow sensor. The load from your air conditioner can also cause sluggishness.
Most of the items mentioned above can be replaced yourself for little cost. Search eBay for lowest prices. My 2000 echo was experiencing sluggishness, I tried almost everything before fixing the problem, which was the fuel filter and pump. I don't know which was the problem, because I replaced them at the same time. Both can be had for around 30 dollars, and they are both part of the same unit, which is inside the fuel tank, and is accessed somewhat easily by pulling up the rear seat cushion (see service manual for details).
A dirty throttle body or worn out mass air flow sensor is really the most likely problem, both are common issues for an echo with more than 100,000 miles. The throttle body can be easily cleaned yourself, mass airflow sensor is also easily replaced.
Stopped up fuel filter.
It could be your MAF sensor. Mass air flow sensor that measures the air going into the intake. This could likely cause sluggish acceleration.
Start at the fuel filter. It may be clogged.
check for tune-up, check maf sensor, check o2 sensors, do a fuel system service.
The Toyota would have more acceleration a= F/m if the mass of the of the Semi Truck is greater than the mass of the Toyota.
Yes a clogged VENT pipe can cause a sluggish drain
I would suspect low fuel pressure would cause both conditions.
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one of two things, the upper o2 sensor or the camshaft position sensor
In this case, acceleration is positive. Negative acceleration would cause the object to slow down (decelerate.)
After a heavy meal, I felt sluggish and had trouble concentrating on my work.
Change your fuel filter.