- stumbles when stopped and accelerating at low speeds

SOURCE: Stumbles on acceleration

Well, I would replace the air filter, make sure the air hose from the air filter to the intake is not kinked or blocked and check for vacuum leaks. If these are all fine, I would check the fuel pressure as it is possible the pump is weak and not supplying enough fuel.

SOURCE: Ford Focus Engine problem

have you tried having your fuel injectors cleaned on it. the engine might not be getting enough gas at take off. it might also be that your gas tank fuel pump or the other fuel pump going bad

SOURCE: A4 Sputtering/skipping when accelerating from stop

sounds like a spark plug or wherte the plug goes into

Harvey N Tawatao

• 3854 Answers
• Posted on Jul 07, 2009

SOURCE: my 2005 ford explorer has acceleration problems

You may have a problem with your MAP sensor. The Manifold Absolute Pressure (MAP) sensor signal is electrically used in a similar way to the use of Mass Air Flow (MAF) sensor signal (although internally it is built differently). It takes a 5 volt signal from the computer, and returns a lower direct current signal in accordance with the vacuum in the engine. A higher output voltage means lower engine vacuum (which means more air flow is occurring), which is then calculated as “more fuel is needed”. Lower output signal indicates higher engine vacuum (which means lower air flow), which requires less fuel. 
It's not just fuel control though. The MAP sensor signal gives the computer a dynamic indication of engine load. The computer then uses this data to control not only fuel injection, but also gear shift and cylinder ignition timing. In some cases it is even used to calculate changes in barometric pressure, to automatically adjust for different altitudes.

The Mass Air Flow (MAF) sensor helps the computer to calculate the flow and mass of the air entering the engine. It does that by measuring the cooling effect of air flow over a heated wire element. The electronic circuit inside the sensor attempts to keep the sensor at a fixed temp.
When it is cooled more by an increased air flow, more current is needed to maintain a constant temperature. The increase in current is converted into a signal to the computer. In most cars this signal would be a high frequency signal. Not as high as a radio wave, but much faster changing than the (relatively) slow frequency of the Oxygen sensor.
During low air flow rates, such as at engine idle, the MAF sensor produces a lower frequency signal. During high air flow rates, such as at wide open throttle-road load, the MAF sensor increases the frequency. The control module then converts these frequencies into their corresponding Grams-Per-Second values.

The MAP or Manifold Absolute Pressure Sensor is a little though expensive device installed in your air intake hose or piping, or installed on the firewall and connected to the manifold with a thin hose. It has 5 or 12 Volts coming in, and it simply senses the vacuum in the manifold and attenuates (reduces, weakens) this incoming voltage by a certain factor. In other words it reduces the voltage in the range of 15% to 60% of the supply voltage (depending on the car's design these numbers will vary), and this varying (but non-pulsing) signal goes to the computer. Too much attenuation kills the engine, it will simply shut off. Yet if you control it correctly you can lean down the mixture from the stoichiometric (a big word that simply means “balance of ingredients”) which is factory set at 14.7:1 (14.7 parts of air to 1 part gasoline) – down to 20:1, maybe even 50:1 or 100:1.
Good luck and hope this helps, in short: you may have a bad MAP sensor and may needs to be replaced.

SOURCE: 2001 toyota 4runner loss of power will not go faster than 40 mph.

MAF bad