420A Help with 2G 1999 Eclipse RS (420a) p0304, p0303, p0302 codes rough idle

[Raider_831]

Hello I have a stock 1999 Mitsubishi Eclipse RS with the 420a engine. It currently has 195,500 miles. I’m currently dealing with a rough idle and check engine lights p0304, p0303, and p0302. None have came on at the same exact same time since I’ll try and fix something and I reset the codes but they eventually return.

I changed the spark plug wires and spark plugs at 178,400 miles with the NGK wires and NGK G-power platinums spark plugs last year in July.

The first code I got was p0303 back in November last year. My mechanic recommended to switch the wires and spark plugs around. I even bought a new spark plug to replace the potential bad one that was in cylinder 3. That seemed to take care of the code for months.

Then last month October 3 the p0303 (for the 2nd time) came on flashing with a rough idle, but it went away by itself and I reset the codes the car seemed to be good again. Then this month November 11 p0304 popped up for the first time with the rough idle but seemed worse.

I drove the car back home, but then my first fix was doing the coil pack and reset the code. Drove the car around town and freeway for a couple minutes but as soon as I made it to town and made a stop I could feel the rough idle at the stop. I came home and told my mechanic to check it out.

Then yesterday when I was going to drive over to my mechanic when I turned the car on the check engine light came on this time p0302 for the first time.

He did the smoke test, his main finding there was the EGR valve potentially smoking a little more than normal, my new oil cap was also smoking. He did the timing belt check he said everything looked good no jumped teeth or damage.

He then finally checked my spark plugs he said they did look like they could be a problem which we bought and replaced, but today the car still seems rough on idle.

He told me to drive it around and see if the check engine light returns. I did buy the fuel injector test kit but he said the injectors looked a little complicated but that we could do it if the light returns.

The mechanics main concern was the code jumping between cylinders and not isolated. Does anyone have any experience with this or have an suggestions on what to do next?

I was dealing with the p0420 code last year as well. Which I took care of this year and replaced the cat and that took care of the smog I passed easily back around May this year.

Thanks in advance

 

[sacrileger]

This information was compiled by AI.

The error codes P0302, P0303, and P0304 correspond to misfires in cylinders 2, 3, and 4 of your 1999 Mitsubishi Eclipse RS with the 420A engine. These misfires could be causing the rough idle you're experiencing. Let's go over the possible causes for these codes and some troubleshooting steps:

Error Codes Breakdown:​

• P0302 – Cylinder 2 Misfire Detected
• P0303 – Cylinder 3 Misfire Detected
• P0304 – Cylinder 4 Misfire Detected

Given that you have multiple misfire codes, it's not likely a single faulty component affecting just one cylinder. Instead, it's likely something affecting multiple cylinders or the overall ignition and fuel system.

Possible Causes for Misfires on Multiple Cylinders:​

1. Ignition System Issues:
   • Spark Plugs: Worn or damaged spark plugs can cause misfires in one or more cylinders. If they are old, they might be struggling to ignite the fuel properly, especially under load.
   • Ignition Coils: If the ignition coils are faulty, they could be sending weak or inconsistent sparks, which would lead to misfires. On a 420A engine, each cylinder has its own coil, so a bad coil could affect multiple cylinders if it's causing a weak spark across the board.
   • Spark Plug Wires: If the wires are old or damaged, they could be causing a weak or intermittent spark, leading to misfires.
2. Fuel System Problems:
   • Clogged Fuel Injectors: If the fuel injectors for cylinders 2, 3, and 4 are clogged or malfunctioning, the fuel-air mixture won't be properly delivered to these cylinders, causing misfires. This could also explain why multiple cylinders are misfiring at once.
   • Fuel Pressure Regulator or Pump: A failing fuel pressure regulator or a weak fuel pump can cause inconsistent fuel delivery. If the fuel pressure is low, it could lead to misfires, especially under load or idle.
3. Air Intake and Vacuum Leaks:
   • Vacuum Leaks: A vacuum leak can affect the air-fuel mixture, leading to rough idling and misfires. If the intake manifold gasket, vacuum hoses, or any other part of the intake system has a leak, it could disrupt the mixture going into multiple cylinders, causing misfires.
   • Dirty Air Filter or MAF Sensor: A dirty air filter or malfunctioning mass airflow (MAF) sensor could cause improper air-fuel mixture ratios, leading to misfires. The MAF sensor specifically helps regulate the amount of air entering the engine, so if it's not reading properly, it could lead to an overly rich or lean mixture.
4. Compression Issues:
   • Low Compression in Cylinders: If the cylinders have low compression due to worn piston rings, valves, or head gaskets, it could cause misfires. You can check compression with a compression tester to see if all cylinders are within normal ranges. This is a more serious issue, but it's worth checking if other causes don’t resolve the problem.
5. Timing Issues:
   • Camshaft or Crankshaft Position Sensor Failure: If either the camshaft or crankshaft position sensor is malfunctioning, the engine may not be properly timed, leading to misfires in one or more cylinders.
   • Timing Belt: A stretched or skipped timing belt could cause misfires if the timing is off. While rare, this could happen if the belt was recently replaced and installed incorrectly.
6. Engine Control Module (ECM) Issues:
   • Faulty ECM: Though less common, a malfunctioning ECM (the engine control unit) could be sending incorrect signals to the ignition system or fuel system, causing misfires. However, this is usually a last resort issue after ruling out the other more common causes.
7. Dirty or Faulty Sensors:
   • Oxygen Sensor: If the oxygen sensor is malfunctioning, it could send incorrect feedback to the engine management system, leading to an improper air-fuel ratio and causing misfires.
   • Coolant Temperature Sensor: If the engine’s coolant temperature sensor is giving incorrect readings, it can cause the engine to run too rich or lean, leading to misfires.

Troubleshooting Steps:​

1. Inspect the Spark Plugs and Coils: Check the condition of the spark plugs. Replace them if they're worn, damaged, or have excessive carbon buildup. Inspect the ignition coils for cracks, corrosion, or other signs of damage.
2. Check the Fuel Injectors: Consider running a fuel injector cleaner or using a diagnostic tool to check if the injectors are operating correctly. If they're clogged or dirty, they may need cleaning or replacement.
3. Check for Vacuum Leaks: Inspect all vacuum hoses and intake components for leaks. You can use a smoke machine or spray carb cleaner around the intake area while the engine is running to check for leaks (the idle should change if there's a vacuum leak).
4. Test Fuel Pressure: Use a fuel pressure gauge to check that your fuel system is delivering the correct pressure to the engine. Low fuel pressure can cause misfires.
5. Compression Test: Perform a compression test on all cylinders to check if the engine has proper compression. If there are low readings on cylinders 2, 3, and 4, you may have internal engine issues like worn rings or valves.
6. Check Sensors: Inspect the MAF sensor, O2 sensors, and coolant temperature sensor. Clean the MAF sensor if necessary and check for any unusual readings from the O2 sensors using a scan tool.
7. Scan for Other Codes: Use an OBD-II scanner to check for any other related codes or freeze-frame data that might provide additional insight into what might be causing the issue.

Possible Solution Based on Common Issues:​

• Replace Spark Plugs: If they're old, replace them with quality plugs.
• Replace Ignition Coils: If coils are worn or faulty, replace them. Sometimes it’s worth replacing all the coils if multiple cylinders are affected.
• Clean Fuel Injectors: If you suspect clogged injectors, use injector cleaner or have them professionally cleaned.
• Check for Vacuum Leaks: Fix any vacuum leaks you find.
• Perform Compression Test: If compression is low, you might need a rebuild or repair work.

By following these steps, you should be able to pinpoint the issue and get your 420A engine running smoothly again. Let me know if you'd like more details on how to carry out any of these tests!

 

[Raider_831]

The error codes P0302, P0303, and P0304 correspond to misfires in cylinders 2, 3, and 4 of your 1999 Mitsubishi Eclipse RS with the 420A engine. These misfires could be causing the rough idle you're experiencing. Let's go over the possible causes for these codes and some troubleshooting steps:

Error Codes Breakdown:​

• P0302 – Cylinder 2 Misfire Detected
• P0303 – Cylinder 3 Misfire Detected
• P0304 – Cylinder 4 Misfire Detected

Given that you have multiple misfire codes, it's not likely a single faulty component affecting just one cylinder. Instead, it's likely something affecting multiple cylinders or the overall ignition and fuel system.

Possible Causes for Misfires on Multiple Cylinders:​

1. Ignition System Issues:
   • Spark Plugs: Worn or damaged spark plugs can cause misfires in one or more cylinders. If they are old, they might be struggling to ignite the fuel properly, especially under load.
   • Ignition Coils: If the ignition coils are faulty, they could be sending weak or inconsistent sparks, which would lead to misfires. On a 420A engine, each cylinder has its own coil, so a bad coil could affect multiple cylinders if it's causing a weak spark across the board.
   • Spark Plug Wires: If the wires are old or damaged, they could be causing a weak or intermittent spark, leading to misfires.
2. Fuel System Problems:
   • Clogged Fuel Injectors: If the fuel injectors for cylinders 2, 3, and 4 are clogged or malfunctioning, the fuel-air mixture won't be properly delivered to these cylinders, causing misfires. This could also explain why multiple cylinders are misfiring at once.
   • Fuel Pressure Regulator or Pump: A failing fuel pressure regulator or a weak fuel pump can cause inconsistent fuel delivery. If the fuel pressure is low, it could lead to misfires, especially under load or idle.
3. Air Intake and Vacuum Leaks:
   • Vacuum Leaks: A vacuum leak can affect the air-fuel mixture, leading to rough idling and misfires. If the intake manifold gasket, vacuum hoses, or any other part of the intake system has a leak, it could disrupt the mixture going into multiple cylinders, causing misfires.
   • Dirty Air Filter or MAF Sensor: A dirty air filter or malfunctioning mass airflow (MAF) sensor could cause improper air-fuel mixture ratios, leading to misfires. The MAF sensor specifically helps regulate the amount of air entering the engine, so if it's not reading properly, it could lead to an overly rich or lean mixture.
4. Compression Issues:
   • Low Compression in Cylinders: If the cylinders have low compression due to worn piston rings, valves, or head gaskets, it could cause misfires. You can check compression with a compression tester to see if all cylinders are within normal ranges. This is a more serious issue, but it's worth checking if other causes don’t resolve the problem.
5. Timing Issues:
   • Camshaft or Crankshaft Position Sensor Failure: If either the camshaft or crankshaft position sensor is malfunctioning, the engine may not be properly timed, leading to misfires in one or more cylinders.
   • Timing Belt: A stretched or skipped timing belt could cause misfires if the timing is off. While rare, this could happen if the belt was recently replaced and installed incorrectly.
6. Engine Control Module (ECM) Issues:
   • Faulty ECM: Though less common, a malfunctioning ECM (the engine control unit) could be sending incorrect signals to the ignition system or fuel system, causing misfires. However, this is usually a last resort issue after ruling out the other more common causes.
7. Dirty or Faulty Sensors:
   • Oxygen Sensor: If the oxygen sensor is malfunctioning, it could send incorrect feedback to the engine management system, leading to an improper air-fuel ratio and causing misfires.
   • Coolant Temperature Sensor: If the engine’s coolant temperature sensor is giving incorrect readings, it can cause the engine to run too rich or lean, leading to misfires.

Troubleshooting Steps:​

1. Inspect the Spark Plugs and Coils: Check the condition of the spark plugs. Replace them if they're worn, damaged, or have excessive carbon buildup. Inspect the ignition coils for cracks, corrosion, or other signs of damage.
2. Check the Fuel Injectors: Consider running a fuel injector cleaner or using a diagnostic tool to check if the injectors are operating correctly. If they're clogged or dirty, they may need cleaning or replacement.
3. Check for Vacuum Leaks: Inspect all vacuum hoses and intake components for leaks. You can use a smoke machine or spray carb cleaner around the intake area while the engine is running to check for leaks (the idle should change if there's a vacuum leak).
4. Test Fuel Pressure: Use a fuel pressure gauge to check that your fuel system is delivering the correct pressure to the engine. Low fuel pressure can cause misfires.
5. Compression Test: Perform a compression test on all cylinders to check if the engine has proper compression. If there are low readings on cylinders 2, 3, and 4, you may have internal engine issues like worn rings or valves.
6. Check Sensors: Inspect the MAF sensor, O2 sensors, and coolant temperature sensor. Clean the MAF sensor if necessary and check for any unusual readings from the O2 sensors using a scan tool.
7. Scan for Other Codes: Use an OBD-II scanner to check for any other related codes or freeze-frame data that might provide additional insight into what might be causing the issue.

Possible Solution Based on Common Issues:​

• Replace Spark Plugs: If they're old, replace them with quality plugs.
• Replace Ignition Coils: If coils are worn or faulty, replace them. Sometimes it’s worth replacing all the coils if multiple cylinders are affected.
• Clean Fuel Injectors: If you suspect clogged injectors, use injector cleaner or have them professionally cleaned.
• Check for Vacuum Leaks: Fix any vacuum leaks you find.
• Perform Compression Test: If compression is low, you might need a rebuild or repair work.

By following these steps, you should be able to pinpoint the issue and get your 420A engine running smoothly again. Let me know if you'd like more details on how to carry out any of these tests!

Some of the things you mentioned I did replace like the coil pack, I did go ahead and replace the spark plugs they had less than (20k miles). My mechanic didn’t clean the injectors or do a compression test which I was hoping for. I will buy fuel injector cleaner and try that I’ve done that in the past.

The car seems to still run rough especially at idle but surprisingly the check engine light hasn’t returned in the 2-3 weeks since I replaced the spark plugs and coil pack. It might just be my motor mounts they are shot even though they’re about a year old. It was the Autozone brands they were no good for me.

By the way my mechanic also checked the timing belt he said it looked fine. Thanks for the response.

 

[BLACK'98DSM]

Your next step should be a compression test. Low compression with a 420A will cause random misfire codes and hesitation. Since your mileage is up there, give it a check. 150psi-250psi is a strong healthy engine. Reading less than 150psi, the engine is usable but plan for the rebuild soon. Reading less than 130psi, the engine will have some problems and should be put out of commission until repairs are performed. It's also a problem to have too much variance between cylinders, which should not exceed 15%. Report back with the readings from all 4 cylinders and we can move forward from there. Diagnostics are better than guess work.

 

[97egl]

Sounds like an EGR partially sticking open. I'm not sure why your mechanic would not be recommending to replace it if its leaking when he tests it

 

[BLACK'98DSM]

A leaky EGR is definitely an issue. However it's open at idle regardless, and the OP was worried about a rough idle. So that would be another issue. He's got a misfire of some sort. Perhaps combined with a leak or excess exhaust gasses.