Rough idle stalls and some times engine dies.P0300

5.7l NOW TOLD 8V ENGINE WITH 16 SPARK PLUGS. OUCH.
THANKS

ok that is USA OBD2 federal code P0300 and means
all cylinders are misfiring OR RANDOMLY ALL.

it really means all cylinders have random weak combustion
THE CAUSES ARE (ASE DAY1 CLASS)
1: BAD ENGINE, WEAK COMPRESSION OR WORSE.50 CAUSES.
2: BAD SPARK , SPARK PLUGS AND OR BOOTS ON COPS
OMG HAS TWIN SPARK COIL PACKS (PAIRS) ODD LOOKING
8 PACKS + 16 PLUGS

3: BAD FUELING OR BAD FUEL. TOO LITTLE OR TOO MUCH

THE PCM DOES NOT KNOW WHY COMBUSTION EGERGY IS LOW
IT ONLY KNOWS IT IS IN TOTAL ON ALL 8 CYLINDER ARE WEAK.
IT MEANS THE PISTONS ARE SLOW TO MOVE, AT FIRE
THEY MOVE SLOWLY, AND WEAK. ALL DO. ALL 8.

LOTS OF CAUSES.
IF ENGINE TESTS PASS, COMPRESSION AND VACUUM AT IDLE SHOWS SAY 20 INCHES HG./ STEADY NEEDLE THEN WE
CONSIDER, NEXT SPARK PLUGS (DONE) AND COP BOOTS NEXT
THE COP BOOTS ARE 17 YEARS OLD AND THEY SURE DO LOVE TO CARBON TRACK THAT OLD!
THE BOOTS ARE SOLD NEAT,(1BY1) X16
HERE
https://www.rockauto.com/en/catalog/chrysler,2007,300,5.7l+v8,1433754,ignition,spark+plug+/+ignition+coil+boot,10150

ID NEVER RUN BOOTS THAT OLD IF ARE. !!!
IF ENGINE IS GOOD (TESTS) AND SPARK TOO
THEN WE WORK FUELING.
CANT BURN FUEL BAD ENGINE OR SPARK ,
EFI ALLOWS WEAR BUT NOT DEAD THINGS. OK?


THE FUEL TEST IN THE SERVICE MANUAL AND ALL EFI BOOKS IN PRINT IS CLEAR AS DAY , THE TEST ALL
FUEL PRESSURE AT IDLE AND WOT CHECKED.
WE DO THE INJECTOR BALANCE TEST
AND THE INJECTOR LEAK DOWN TEST.
11 TESTS ON A V8, NO GUESSING WE JUST DO THE TEST
OR BUY NEW INJECTORS IF RICH./
OR BATH IN FUEL GUESSING PUMP BAD. WEAK)

I AM NOT SAYING ALL 8 INJECTORS FAIL
SO PUMP PRESSURE TEST ARE NEXT.
OR FIRST IF YOU HAVE THE TOOLS
MANY A TECH DOES 4 TEST WITH TOOLS IN ORDER OF SPEED OF TEST. VACUUM. AND FUEL PRESSURE ARE FAST
BUT IS READY TO DO THEM ALL . OR GOES BROKE GUE$$
SCAN TOOL IS FIRST AND DONE.
COMPRESSION TEST IS TEDIOUS. X8, DONE WITH FUEL PUMP RELAY OR FUSE PULLED AND DONE WOT, AND ALLOW NEEDLE TO PEAK. 150 PSI OR BETTER X8
THE PUMP FUEL IS RATED MIN, 105.0 psi
REG IS IN TANK PUMP.

MY GUESS IS LOW FUEL PRESSURE. BUT IS ONLY A GUESS
I DO THE THE TESTS, NOT GUESSING 50 TIMES.

SYMPTOM 1: ROUGH IDLE IN THE COLD

The engine will not idle smoothly, or it stalls during idle when the engine is cold. When the engine is cold and you take your foot off the gas pedal, the engine runs very rough and may even stall. When you run the engine at higher speeds, it seems to run fine, or at least it runs more smoothly.
Possible causes:

1. If you have a carburetor, you may have a bad accelerator pump or power circuit.
   The Fix: Replace accelerator pump or replace the carburetor.
2. There may be a vacuum leak.
   The Fix: Check and replace the vacuum lines as required.
3. There may be some type of ignition problem.
   The Fix: Check and replace the distributor cap, rotor, ignition wires, and spark plugs.
4. The ignition timing may be set wrong.
   The Fix: Adjust the ignition timing.
5. There may be a fault in the computerized engine control system.
   The Fix: Check engine control systems with a scan tool. Test the circuits and repair or replace components as required.

1. The EGR valve may be bad.
   The Fix: Replace the EGR valve.
2. The engine may have mechanical problems.
   The Fix: Check the compression to determine the engine's condition.
3. Idle speed is set incorrectly.
   The Fix: Set idle speed to the car's original settings.
4. The fuel injectors may be dirty.
   The Fix: Clean or replace the fuel injectors.

SYMPTOM 2: ROUGH IDLE WITH WARM ENGINE

The engine will not idle smoothly, or it stalls during idle when the engine is warm. When the engine is warm or hot and you take your foot off the gas pedal, the engine runs very rough and may even stall. When you run the engine at higher speeds, it seems to run fine.
Possible causes:

1. If you have a carburetor, you may have a bad accelerator pump or power circuit.
   The Fix: Replace accelerator pump or replace the carburetor.
2. There may be a vacuum leak.
   The Fix: Check and replace vacuum lines as required.
3. The fuel pressure regulator may be operating at too low a pressure.
   The Fix: Check the fuel pressure with a fuel pressure gauge. Replace fuel pressure regulator. (This is not really a do-it-yourself kind of job.)
4. Idle speed set incorrectly.
   The Fix: Set idle speed to specs.
5. There may be some type of ignition problem.
   The Fix: Check and replace distributor cap, rotor, ignition wires and spark plugs.
6. There may be a fault in the computerized engine control system.
   The Fix: Check engine control systems with a scan tool. Test circuits and repair or replace components as required. (This is not really a do-it-yourself kind of job.)
7. The EGR valve may be bad.
   The Fix: Replace EGR valve.

1. The engine may have mechanical problems.
   The Fix: Check compression to determine engine condition.
2. The fuel injectors may be dirty.
   The Fix: Clean or replace fuel injectors.

SYMPTOM 3: FAST IDLING

The engine idles too fast. After the engine has run long enough to become warm, the idle speed does not come down to normal. You really notice it when you come to a stop and must have to push ******* the brake pedal to keep the car from moving.
Possible causes:

1. If you have a carburetor, you may have a bad accelerator pump or power circuit.
   The Fix: Replace the accelerator pump or replace the carburetor.
2. The engine may be overheating.
   The Fix: Check and repair the cooling system.
3. The fuel pressure regulator may be operating at too low a pressure.
   The Fix: Check fuel pressure with a fuel pressure gauge. Replace fuel pressure regulator. (This is not really a do-it-yourself kind of job.)

1. The ignition timing may be set wrong.
   The Fix: Adjust the ignition timing.
2. There may be some type of ignition problem.
   The Fix: Check and replace the distributor cap, rotor, ignition wires and spark plugs.
3. There may be a fault in the computerized engine control system.
   The Fix: Check the engine control systems with a scan tool. Test the circuits and repair or replace the components as required.
4. There may be a vacuum leak.
   The Fix: Check and replace vacuum lines as required.
5. You have a bad idle speed control unit.
   The Fix: Replace the idle speed control unit.
6. The alternator may not be working properly.
   The Fix: Replace the alternator.

SYMPTOM 4: STALLING UPON STOPPING

Car stalls when stopped quickly. You are driving along and everything is just fine ... until you let off the gas pedal and apply the brakes. The engine starts shaking and may even stall. Not a good thing to happen because you lose power steering when the engine dies and could risk an accident.
Possible causes:

1. There may be a serious vacuum leak.
   The Fix: Check and replace the vacuum lines as required.
2. There may be a fault in the computerized engine control system.
   The Fix: Check the engine control systems with a scan tool. Test the circuits and repair or replace the components as required. (This is not really a do-it-yourself kind of job.)
3. Broken linkage.
   The Fix: Repair or replace the linkage as required.

Idling issues can be very frustrating, but with some patient troubleshooting, you'll have a real chance at figuring it out. Remember to always check your engine idle with the air conditioning and defroster turned off, as both of these systems are designed to change the idle when they are on due to the air conditioning system's demands on the engine.

P0300 is a random or multiple cylinder misfire, and P1381 is a misfire EBCM (Electronic Brake Control Module) or PCM (Powertrain Control Module) Since you mentioned replacing fuel components, it could be as simple as a fuel injector being clogged up causing a cylinder misfire. Have you checked your fuel injectors?

I have encountered this before and it was the vacuum supply line from intake to the fuel pressure regulator sucking fuel through regulator. it could also be more serious like intake gaskets

The "rough idle" symptom encompasses many systems in the vehicle, which must all be checked. Is the "Check Engine" light on? Have you had the codes read? (Codes can be read and interpreted on your Cadillac using the air conditioning controls, the procedure for which can be found online using any search engine.)

Generally, especially on a car as old as yours, you will most likely need a MAJOR TUNE-UP. You will need to check all of the following:

• Condition of the fuel in the gas tank (especially if the car sat dormant for six months or more);
• Operation of the idle air bypass (Idle Air Controller);
• Cleanliness of the throttle body and its components;
• Condition of the fuel delivery system, including the fuel filter, pressure regulator, electric fuel pump, and injectors (this is the most likely suspect here);
• Condition of the coil packs or distributor cap and rotor (I don't remember which your car has);
• Condition of the spark plug wires;
• CONDITION OF THE SPARK PLUGS (obvious);
• Operation of the ECU (or whatever you prefer to call the computer that controls your engine);
• Presence of any vacuum leaks or cracks in the intake manifold.

START BY REPLACING YOUR FUEL FILTER, then check for proper fuel pressure at the fuel rail. Replace the pressure regulator as necessary and, if you are not getting enough fuel pressure, it is possible that rust and debris in your fuel tank has clogged the intake strainer and may have damaged your electric fuel pump. Once you have eliminated fuel delivery issues, continue by examining your ignition system (plugs, wires, etc.).

Best of luck to you!

Should be on or near the fuel injector supply rail.

Try this:
-Check fuel pressure. (read in its repair manual to see how much it suppose to be.) If it's low then the fuel pressure regulator or fuel pump is defect.
-Is it fuel injector...? Then check its resistance of each injector when it's cold. If it's not within its specification then replace new one

Good luck

Mai

here are a few possibilitys, a bad fuel pressure regulator . the vehicle runs rough, the engine will not start ( usually in mornings ) many times engine starts but stalls shortly after starting. a bad regulator can result in fouled plugs. replacement is only cure. black soot on plugs, blake smoke from tailpipe, running rough, stalling. make sure fuel filter is not plugging up. or low fuel pressure from fuel pump. check fuel pressure regulator first. have a good day !! the regulator if bad will cause an instant drop in fuel pressure when turned off. and it will cause a delay in building sufficient fuel pressure,.when starting.

Check the fuel pressure it could be the fuel pump or pressure regulator.

I have a 1994 Cadillac Eldorado and every time i start it the car has rough Idle and the Idle fluctuate's. I also can feel it in the gas pedal when the car is doing this I tried replacing the throttle body sensor but it still does it I also was told it was the Idle error sensor. So instead of spending the unecessary money again I thought I would go online and see if anyone could help me with this problem.