Skip the auto shop - Our mechanics make house calls

Q: It sputters bad when i hit the gas pedal to hard and want to die

asked by on

When the engine is cold it doesnt run half bad but once it warms up i got to baby the gas pedal or it wants to die

My car has 200000 miles.
My car has an automatic transmission.

A: When an engine is cold, it needs to have ri...

When an engine is cold, it needs to have rich fuel condition to run. Only when the engine has warmed up can it run at full power and efficiency. The thermostat not only keeps your motor from overheating, but it also keeps it running at an optimum temperature. From an engineering perspective, gas motors actually run a few degrees to cold to maximize there fuel mileage. If motors ran at higher temperatures, the metal and gaskets begin to fail much faster. So there is a balance that has to be maintained. Hot enough for greater efficiency and cool enough not to damage gaskets and other materials under the hood.

For a cold motor to run, it must have a rich fuel mixture, or it just won’t run. The choke was the first solution to this problem. If your not aware, the choke was a second throttle plate that restricted the amount of air entering the motor, but the amount of fuel did not change. The ratio between air and fuel has effectively changed. On modern fuel injected engines, the computer manages the motor in what is called open loop. It is using a set program for cold running instead of actively making fuel and air changes to optimize the motors running.

Your car runs well when cold. We can conclude that this is due to the rich fuel condition present with a cold motor. So the question you need to answer is, is there to much fuel when it warms up, or is there to much air?

A couple of possibilities come to mind. First would be the coolant temperature sensor. If it is giving the computer the wrong reading, the computer will think your truck is cold when it is not. This can cause numerous issues. But one thing that makes me doubt this, is the need to baby the gas pedal. Usually when there is plenty of fuel, giving it more throttle will result in strong acceleration.

The next likely possibility is the MAP sensor. This is one of the primary sensors the computer uses to calculate fuel mixture. The PCM (Powertrain Control Module) will not use it when it is cold. It will have a vacuum hose attached to it and an electrical connector with several wires. Make sure the vacuum hose doesn’t have a hole in it, or isn’t plugged. When you disconnect it fro the MAP sensor when it is running, you should feel a vacuum. If not, you know where to look. Check for damaged wiring or connector.

Next, you could have a vacuum leak. This can be in the intake manifold, a vacuum hose, or a the throttle body. There are several ways to check for this. You can use a smoke machine, which is expensive, or you can use some starter fluid, brake cleaner, or carburetor cleaner. Spray it around the anywhere there might be a vacuum leak. If the motor changes RPM when you spray in a specific spot, you are on the right track. Your looking for a vacuum leak. Spray sparingly. If you fog the entire engine compartment, you won’t know if it is just being sucked into the throttle body, or an actually vacuum leak.

A good trick to be sure your not chasing a phantom vacuum leak, is to add propane into the intake while driving. If the motor responds well to the addition of propane while driving, you can be sure you have a lean running condition. Which I believe is the most likely problem here. You will need to use a long vacuum hose with a valve on the propane bottle to add propane while driving. This takes some creativity, but is a very valuable test when diagnosing such a problem.

Good luck. I hope I have given you a diagnostic track to follow that helps you figure it out. However, feel free to contact a certified mechanic if you need help with these checks. They will be able to diagnose why your car is dying firsthand and fix it accordingly.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Stablity control warning light on constantly

I agree that technology breeds a love and hate relationship, my advice is to concentrate on the loving and leave the hate behind. The issue with your vehicle may be a somewhat straightforward repair. GMC is aware of a corrosion...

Q: Engine quits at any speed even when idling - 1990 Mercedes-Benz 300 CE

Hey there, thanks for writing in. You will need to verify to see if the problem is in the ignition module not giving spark when the engine dies. If no spark is given, then the most common cause of the...

Q: When I unplugged the TPC it runs like a new truck

Hi there. If when you remove the TPS (throttle position sensor) and the engine runs better, then there could be an issue with the MAP (manifold absolute pressure) sensor. Check the MAP sensor and see if the harness is good...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the P0052 code means This code is seen when the Engine Control Module (ECM) tries to control the...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...