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P0300 Multiple Cylinder Misfire Diagnosis for 1998 Sunfire 2.2L - Ignition, EGR, or Wiring Issues?

Model: 98 Sunfire 2.2L Fault Code: P0300 Posted: 2007-03-16 18:27

I own a 1998 Ford Sunfire with a 2.2L engine. Recently, the vehicle has started running very rough at idle, especially after prolonged driving. The issue occurs intermittently—shutting off and restarting the car temporarily resolves it. However, over time, the misfiring persists and now the engine struggles to maintain idle without my foot on the gas pedal. I've already replaced all coil packs, which did not resolve the problem. Given that the OBD2 code P0300 (Multiple Cylinder Misfire) is present, I'm wondering what other potential causes could be at play. Possible suspects include: the ignition control module, EGR valve malfunction, or wiring harness issues—especially since some 2.2L models have known electrical problems in the PCM wiring harness. The engine may also experience random misfires due to fuel delivery inconsistencies caused by faulty sensors like the TPS (Throttle Position Sensor) or O2 sensor. I'm looking for reliable troubleshooting steps and common fixes specific to this model year and engine configuration. Any insights on how to diagnose these components effectively would be greatly appreciated.

Related fault codes
P0300
Comments (13)
Anonymous 2007-03-17 10:12

The ignition control module is a likely culprit in 1998 Sunfire models—especially if the misfire persists after coil pack replacement. Additionally, a slipped timing chain could cause irregular combustion and should be checked during engine inspection.

Anonymous 2007-03-17 16:40

I removed the EGR valve on my 1998 Sunfire and found it was fully open with carbon buildup stuck inside. After cleaning it thoroughly and installing a new gasket, the vehicle has run smoothly ever since—this suggests EGR-related misfires can be a major factor in P0300 cases.

Anonymous 2007-04-05 09:42

I have a 2000 Sunfire with a 2.2L engine experiencing P0300 multiple cylinder misfire. I replaced the catalytic converter, plugs, and wires—though the code remains. Where is the EGR valve located? I'd like to inspect it next. Could the ignition coil be another root cause?

Anonymous 2007-04-06 13:05

Refer to http://www.alldata.com for detailed diagnostic procedures on 1998-2000 Sunfire models, including EGR and ignition system troubleshooting.

Anonymous 2007-04-06 13:23

P0300 indicates random, multi-cylinder misfires—this can stem from many sources. First, ensure plugs and wires are properly installed and functioning. The EGR valve is typically located near the exhaust manifold, with a tube branching off to the intake manifold. You may need to visually inspect it; if you're unsure, describe its location for further troubleshooting guidance. Some diagnostics require an OBD2 scanner, which can help identify specific fault patterns.

Anonymous 2007-06-18 13:03

Hi, new user here—my 2000 Cavalier with a 2.2L engine has been experiencing random power loss over the past few months. The car doesn’t stall but misfires unpredictably. I recently scanned it and saw P0303 and P0122 codes. After clearing them, the car ran fine for about 15 minutes before returning to P0300. I’ve replaced plugs, wires, and the front O2 sensor. The P0122 code appears related to the TPS sensor. Any suggestions on where to look next? I’m leaning toward a faulty ECU but would appreciate any input.

Anonymous 2007-06-18 14:21

If P0122 is intermittent, it may be causing rough idle and power loss. When the throttle position sensor (TPS) reports an incorrect signal—such as thinking the throttle is closed when it’s actually open—the engine delivers improper fuel mixtures: rich or lean conditions leading to random misfires. Start by testing and replacing the TPS sensor.

Anonymous 2007-06-19 11:28

Thanks for the reply. What's confusing is that previously I saw P0303 with front O2 sensor issues, then later P0122 and P0303 together. After clearing those codes, only P0303 remained. Also, after driving for a while, if I’m stopped in neutral, the RPMs stay around 1500 instead of dropping to normal idle (around 800). This behavior suggests an underlying sensor or control issue—perhaps not just a simple ECU failure, but something deeper like wiring or fuel delivery problems.

Anonymous 2007-06-19 11:50

Some early 2.2L Cavalier and Sunfire models had known wiring harness issues at the PCM. Before jumping to an ECU replacement, verify basic systems: fuel pressure, compression tests, cylinder leakage, EGR operation, and sensor readings. These foundational checks are essential for accurate diagnosis.

Anonymous 2007-06-26 06:31

I’ve replaced the TPS sensor but still experience misfiring. Is there an aftermarket wiring harness kit available that can fix this? I’m especially concerned because the issue worsens during rain—this strongly points to moisture-related electrical faults in the harness.

Anonymous 2007-06-26 06:49

Check with your local Chevrolet dealer for a revised wiring harness or TSB (Technical Service Bulletin) related to P0300 and intermittent misfire issues on 2.2L engines. Resources like http://www.alldata.com can also provide model-specific repair guidance.

Anonymous 2007-06-26 07:13

Thanks Jeff—do you have a recommendation for a Chevrolet dealer in Ottawa? I’m located about 20 minutes east of Orleans.

Anonymous 2007-06-26 10:13

Marcel Belanger (Pontiac/Buick) is directly across from my local dealer, and Mew Chev Olds is just around the corner. Both have solid reputations based on personal experience. If you provide your OBD2 code to a service advisor and mention that sensors have already been replaced, they can estimate their diagnostic process and initial repair costs. The parts department may also have access to relevant TSBs for 1998–2000 Sunfire models.