Question about 2003 Chevrolet Impala

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P0300 and rough or no run 2003 Impala 3.8

Rplaced: Fuel Filter Cat Converter O2 Sensor MAF Sensor Plugs Wires Ignition Module PCM Upper Intake Manifold and related If I hold RPM steady and elevated it runs smooth and code vanishes. Any load or idle causes rough run and then quits. WTF?

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Fuel regulators are notorious for going bad in them maybe start there

Posted on Dec 05, 2012

  • Bob Plance Dec 05, 2012

    Will try fuel reg and press next. Must get gauge first.

  • Bob Plance Dec 07, 2012

    Brian, I unplugged the vacuum to the fuel regulator and It continued to run, although the RPM changed some. There was no fuel and I could feel vacuum. I unplugged the MAP and no major change but it was just replaced. I obtained a fuel pressure tester and the readings engine off key on and runnng are within specs. I am going to re-torque the intake manifold in case I screwed that up when I replaced it. The strange thing about this is that I can start the engine and it will idle with a little miss for ever but if I accellerate it then let off it will quit. I am now getting Codes comming and going including P0134 and P0135 (the O2 sensor is new) and of course the dreaded P0300. I have to do these things in between work and weather as I am outside in the rain.


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Unplug the fuel pressure regulator and see if fuel is leaking into the intake or check the fuel pressure also try unplugging the map and mass one at a time and vice versa this engine should run off either one when a one or the other has an open circuit no mention of coil packs did they test good you should get a good 50kv bright blue spark from each terminal min of 30 kv if you dont have a tester thats about 1/2 in or better in length be careful coil packs can produce enough amperage to kill you

Posted on Dec 05, 2012


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Posted on Jan 02, 2017

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SOURCE: Rough idle code P0300

check the fuel pressure when u get a po300 code that means there has been a missfire. if your fuel pressure is low it will cause missfires.

Posted on Mar 08, 2009

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SOURCE: 89 Corsica: no power, hesitates in drive, idles

Check your fuel pressure, and or injectors. You may have too much fuel getting into the engine causing it to burn rich and overheat the converters.

Posted on Apr 26, 2009

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SOURCE: 98 blazer 4.3 4x4. runs very rough. scan code

ethanol gas problem. add a can of SEAFOAM to tank of Premium gas. change fuel filter after 100 miles. then add SEAFOAM 3-5000 miles to keep fuel line/system;emissions, and valves clean of ethanol goop and water which is created by this awful ethanol mixture.

Posted on Aug 31, 2009

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SOURCE: Rough idle stalls and some times engine dies.P0300

a car that idles rough and clears up is the sure sign of an o2 sensor shorted this may not give a code if the short in the sensor is bad the computer will eliminate its input to protect itself

Posted on Sep 03, 2009

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SOURCE: 98 Chevy Tahoe 5.7 liter engine cuts out and

Have you checked for vaccume leaks?
You've got lots of parts in there, Has the problem been the reason you have replaced all of those, or did it come up while doing some of the repairs?

Posted on Dec 18, 2009

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1 Answer

What are the probable causes of DTC P0300 on this unidentified vehicle?

plugs, wires, coils, low compression, bad pcm, improper fuel pressure, bad fuel, worn out cam, plugged injector, plugged cat, bad O2 sensor, bad MAF, and Vacuum leaks can cause multiple cylinder missfires along with many other things

Aug 15, 2015 | Cars & Trucks

3 Answers

Engine code p110

P0303 Code - Cylinder #3 Misfire
P0110 DTC - IAT Circuit Malfunction
P2195 O2 Sensor Signal Biased/Stuck Lean (Bank 1 Sensor 1) Code
Potential causes of a P2195 code include:
  • Oxygen (O2) or A/F ratio sensor or sensor heater malfunction
  • Open or short in O2 sensor circuit (wiring, harness)
  • Fuel pressure or fuel injector problem
  • Faulty PCM
  • Intake air or engine vacuum leaks
  • Faulty fuel injector(s)
  • Fuel pressure too high or too low
  • PCV system leak/fault
  • A/F sensor relay faulty
  • MAF sensor malfunction
  • ECT sensor malfunction
  • Fuel pressure too low
  • Fuel leak
  • Air suction in air intake system
  • A code P0303 may mean that one or more of the following has happened:
  • Faulty spark plug or wire
  • Faulty coil (pack)
  • Faulty oxygen sensor(s)
  • Faulty fuel injector
  • Burned exhaust valve
  • Faulty catalytic converter(s)
  • Running out of fuel
  • Poor compression
  • Defective computer
  • Potential causes of the P0110 DTC include:

  • po110
    • IAT sensor shifted out of airflow
    • Bad IAT sensor
    • Shorted to ground or open on signal circuit to IAT
    • Open in ground circuit to IAT
    • Poor connection at IAT (backed out terminals, broken connector locks, etc.)
    • Bad PCM

Sep 25, 2014 | 2003 Ford Focus

2 Answers

Rough irratic idle. have replaced air filter, plugs, fuel filter, top and bottom o rings on injectors, #4 injector,Idle air control, MAP snsr, intake air snsr, upstream o2 snsr. had GM do a scan. they...

throttle position sensor, egr valve, coolant temp sensor, but really unless you are having a problem with the PCM it would show a code if any of those were out.

possibly a weak fuel pump? you would want to find out the operating pressure for your vehicle and either test it or have it tested if you are nervous around the fuel system

the fuel filter you changed, was it inline or in the tank? most of todays vehicles will have a filter mounted on the fuel pump inside the tank, some have both in-tank and inline.

just a few thoughts,
hope this helps!

May 24, 2011 | Pontiac Sunfire Cars & Trucks

3 Answers

My 2000 chevy silverado has ap0300 misfire code , how do i fix ti

P0300....Random/Multiple Cylinder Misfire Detected

so its got a misfire and quickest way out here to avoid a expensive garage visit is to change plugs and Ht leads and see what happens ,HT leads is proper english for fire wires by the way ,see iam learning american ---slowly---

Mar 12, 2011 | Chevrolet Chevy Cars & Trucks

2 Answers

My 2003 Pontiac Bonneville has a fault code of p0300 random cylindar misfire. How would you go about fixing it?

A code P0300 may mean that one or more of the following has happened:
* Faulty spark plugs or wires
* Faulty coil (pack)
* Faulty oxygen sensor(s)
* Faulty fuel injector(s)
* Burned exhaust valve
* Faulty catalytic converter(s)
* Stuck/blocked EGR valve / passages
* Faulty camshaft position sensor
* Defective computer

Possible Solutions:
* If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.
* If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.

Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open.

Hope helps (remember to rate this).

Oct 11, 2010 | Pontiac Bonneville Cars & Trucks

1 Answer

04 chevy blazer obd codes p0101 and p0300 changed wires plugs distributor maf pulled cat and muffler tried crank sensor and ignition module. at first wouldnt go over 20 mph then wouldnt start. did full...

change your O2 sensors. Try the airfitler, fuel filter and make sure your getting sufficient fuel pressure.


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May 30, 2010 | Chevrolet Blazer Cars & Trucks

1 Answer

P0102 Grand Prix

P0102 is ---- mass or volume air flow circuit, low input.
Check the wires going to the maf sensor and at the connection. If all seems ok, you might need a new sensor, seeing how it ran a little better when disconnected.

Jul 15, 2009 | 2003 Pontiac Grand Prix

3 Answers

2001 GMC Jimmy Idling rough

P0300 is multiple misfires.
P0171 is lean burn on left bank 1 means drivers side
02 sensor is faulty. Your vehicle is over fuelling that is why your are getting P0300 code and the rotten egg smell. Good idea is to replace both 02 sensors.

Apr 04, 2009 | 2001 GMC Jimmy

2 Answers

Rough idle P0300

a faulty MAF will not cause a P0300, just a severe loss of power, look for injector, ignition and intake vacuum leaks as your causes.

Mar 20, 2009 | 2000 Chevrolet Impala

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