Engine Hesitates, Stumbles, Lacks Normal PowerCar accelerate slowly when gas pedal is depressed
You’re driving along in your vehicle, and everything seems fine – until you start up a hill, or try to quickly pull out into fast-moving traffic. Then it happens… nothing. Sure, the car is moving, but it’s ridiculously slow and you can tell that the engine is struggling to keep up.
This is a common problem found especially in high-mileage vehicles. Before you get too worried, let’s take a look at some of the possible easy fixes….
– The O2 sensor. The oxygen sensor (or O2 sensor) is a device that helps monitor the emissions of your vehicle so as to analyze the air-to-fuel ratio going through the engine In a nutshell, you need to proper amount of oxygen to properly burn the fuel in the engine. Not enough oxygen results in unburn fuel (rich mixture) and too little oxygen (lean mixture) causes more pollutants and can actually damage your engine. When this sensor detects a problem, it sends a signal to the engine to change the amount of fuel being used. If your sensor is malfunctioned, it could be messing up your fuel mixture; and if it’s out altogether, your car’s pretty much just guessing as to what mixture it needs at the moment.
- Fuel filter. Changing the fuel filter (especially if it’s been a while) may be your ticket here. If fuel can’t get into the engine, you’re not going to be getting anywhere very quickly. In addition to this, it’s not a bad idea to get an injector flush altogether.
– Clogged air filter or blocked exhast. Air is a very important part of proper car function (or any type of combustion, for that matter). Make sure your engine’s getting the necessary amount of oxygen it needs to operate.
- Timing belt. If this is off by even 1 tooth, it can cause acceleration problems.
And of course there are many other possibilities –
Fuel pump may need to be replaced
Transmission may need some work
A slipping clutch could be the culprit.
The computer uses this information to determine how much fuel is needed to maintain the correct air/fuel mixture, and when extra fuel is needed if the throttle suddenly opens wide.
Throttle Position Sensor (TPS) full range test
Mass Airflow (MAF) Graph and Fuel Trim Readings
Lean Fuel (P0171, P0174)
Throttle Position (P0120 or P0124) or (P0222 or P0229)
An engine that hesitates, stumbles or misfires when accelerating or when it is under load, is an engine that is either sucking too much air, not getting enough fuel, or misfiring. If the Check Engine Light comes on, you may find any of the following codes:
P0171, P0174 Lean fuel condition codes
P0120 to P0124 Throttle position sensor codes
P0222 to P0229 Throttle position sensor codes
P0400 to P0409 EGR related codes
If there are no misfire codes, a common cause of acceleration stumble is a bad throttle position sensor (TPS). The TPS tells the computer how far the throttle is open. The computer uses this information to determine how much fuel is needed to maintain the correct air/fuel mixture and when extra fuel is needed if the throttle suddenly opens wide.
Another common cause are dirty fuel injectors. If varnish deposits have built up in the tips of the injectors, they won’t spray as much fuel as they normally do, or will “dribble” fuel instead of spraying a fine mist. This creates a lean fuel mixture and conditions that are ripe for stumble and hesitation (also misfire). Look at short term fuel trim (STFT) and long term fuel trim (LTFT) with your scantool. If the numbers are high, it tells you the engine is running lean and the injectors need cleaning. Treat mild cases with a high quality fuel-injector cleaner additive. Severe cases require professional cleaning equipment. Other problems that cause acceleration stumble include vacuum leaks, low fuel pressure, a weak spark caused by low coil voltage or bad coil(s), retarded ignition timing, and contaminated gas.
Look at the following with your scantool : throttle position, mass airflow (MAF), short term fuel trim (STFT), long term fuel trim (LTFT), ignition timing, and fuel pressure (if a PID is available). Throttle Position Sensors (TPS) typically wear in the idle and just above idle positions, but they may also have dead spots at any point in their range of travel. With the key on, engine off, graph the sensors output while slowly opening the throttle all the way. The graph should look like a relatively smooth ramp, with no suddenly drops or flat spots.
A seemingly unrelated issue that surprises even the most experienced mechanic
For best results, taking your car to a trusted mechanic for his evaluation my be in your best interest to get to the root of the problem before wearing yourself out trying to address the issue through a costly trial-and-error process – which could result in new problems if not properly handled by someone with proper knowledge and experience.
This Will Help.