Skip the auto shop - Our mechanics make house calls

Q: Rough start/idle plus loss of power

asked by on

The car is experiencing hard start only when it's cold and from time to time it had rough idle which gets rougher when the car is in gear. I've replaced fuel and air filters. Also car has loss of power when I punch it. I ran diagnostics and the car. Some back with whole bunch of codes for miss fires P0300-P0306, fuel pressure regulator performance P2293. I might also add I'm terrible at maintaining the car and have a oil leak :(((

My car has 125000 miles.
My car has an automatic transmission.

Hi There, This is an indication of a fuel pressure problem as indicated by the codes you have pulled. The fuel pressure regulator is a device which controls the pressure of fuel supplied to the fuel injectors on an engine. This works by bleeding off a portion of the fuel flow to the injectors from the fuel pump to control the fuel pressure. Fuel is pumped from the fuel tank to the fuel rail by the fuel pump. The fuel pressure regulator is normally mounted after the fuel rail to ensure that the fuel rail has priority in fuel flow. The valve in the regulator controls the amount of fuel that is bled from the fuel rail by opening an outlet port to allow fuel to flow back into the fuel tank. All injectors need a pressure difference between the inlet and the outlet of the injector to spray fuel into the combustion chamber. This is called the base pressure. The base pressure is adjusted via the adjustment screw to suit the injectors and specific fuel pump system you are using. The adjustment screw pushes down on a spring which applies a force onto the valve. When the pressure inside the bottom chamber of the regulator exerts a high enough force on the valve to overcome the spring force and lift the valve off its seat, it allows fuel to flow through the outlet port effectively controlling the fuel pressure in the fuel rail. Since the outlet of the injector is exposed to manifold vacuum/pressure which varies depending on throttle movement, but the flow of fuel from the fuel pump is constant, the valve needs a reference to continuously change the amount of fuel bled to maintain constant fuel pressure to the injectors. I would suggest having an expert from YourMechanic come to your location to diagnose and inspect your vehicle.

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

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

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: Slight engine tick, not a bad sound in one but I'd just like if k could fix it.

There are few situations that require the engine to be revved to 2200 rpm when the transmission is in neutral. Some small ticking noises can come from exhaust leaks at the exhaust manifold. One thing some people try to do...

Q: Ignition broken

Hello, from what you describe, it sounds like they used a slide hammer on the ignition switch and broke it. When damaged, these ignition locks can be extremely difficult to be removed. Mercedes lists some of the parts like the...

Q: When idling my car overheats?

Claimed by John Hege

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.