OBD2 P0300 Multiple Cylinder Misfire Diagnosis for 2004 Dodge Neon - Fix & Solutions

The brand and quality of your spark plugs and ignition wires matter significantly. Using low-quality parts—even if they're not the cheapest—can cause persistent misfires in a 2004 Dodge Neon, which is known for being sensitive to ignition system components. The engine may run fine under load but still produce a P0300 code due to misfiring. I've worked on many Neons at dealerships and can confirm this issue. Please share the exact part numbers you used so we can verify compatibility. Keep me posted—good luck!

I had my oil changed recently, and during that visit, I also had a fuel injector cleaning service performed. Afterward, my car actually started acting worse—when stopped at traffic lights, the check engine light would flash and the idle became unstable. So today, I took it to a mechanic who ran diagnostics using an OBD2 scanner. They confirmed the issue is still present. I’ll update you once I get their findings.

If your check engine light is flashing, that indicates severe misfiring—this is a serious warning sign. Who performed the last tune-up? Were all spark plug wires securely connected at both ends (coil pack and plug)? Did you properly gap the spark plugs according to manufacturer specifications? Knowing exactly what parts were installed would help diagnose this accurately.

The shop ran diagnostics and confirmed that the coil packs are functioning correctly. I’m now replacing the spark plugs with higher-quality ones, as recommended. I told my boyfriend about your earlier advice—he didn’t believe it at first and spent $50 to have a mechanic check the parts. Well, it turns out we were both right: proper parts matter. Once I install the new plugs, I expect the issue to resolve. Thanks for the help! If it doesn't work, I’ll update you.

The correct spark plugs for a 2004 Dodge Neon are typically Champion brand (specifically part # 13796), and they cost less than $20 each. The Neon engine is very specific about ignition components—many people don’t believe me when I say this, but using inferior parts or improper installation can cause misfires. It’s frustrating how often people waste money on unproven services. I’ve fixed dozens of these cars—most times the real issue lies in part selection and installation quality. I’d love to see more users trust expert advice over store-brand recommendations. Good luck, and keep me posted!

I installed Champion Platinum spark plugs as suggested, and my car has been running smoothly ever since. Thanks for the helpful guidance—this fixed it completely.

How much did the fuel injector cleaning service cost?

It was $80!

I hate to see people spend their hard-earned money on services that only fix misfires about 3% of the time. While it's not a bad service, it’s often ineffective—especially when the root cause is incorrect parts or installation. I’m glad your issue was resolved with proper spark plugs and diagnostics. If you have any further issues, let me know. By the way, have you checked your control arm bushings yet? They can wear out over time and affect engine performance.

I agree—what are control arm bushings? Should I consider replacing them?

The front control arms’ rear bushings tend to separate and create a clunky, noisy sound in the front end. If your car hasn’t had these replaced, at least one is likely worn out. I might be able to share an image if needed.

The check engine light came back on just a week after installing new spark plugs. It seems the issue wasn't resolved—what else could it be? Alison

Is the same P0300 code still present? A 2004 Dodge Neon engine is highly sensitive to ignition components. Using platinum spark plugs—even from reputable brands—is not recommended; they can cause carbon tracking and misfires. Sometimes removing wires to inspect plugs breaks the connection, leading to a misfire. Other common causes include improper plug gap, loose wire connections at coil packs, or oil contamination on spark plug boots—this can cause immediate misfiring. If there’s engine oil on the boot, you’ll need a tube seal for that cylinder. Also verify that the coil pack is properly functioning and that compression tests are normal. The garage that said it was just the plugs may have missed key details—diagnosing and repairing requires professional expertise. I recommend having a qualified mechanic re-check all components: proper part selection, correct installation, and full diagnostics (head gasket, injectors, coil function). A P0300 code is one of the easiest to diagnose but can be costly if not handled correctly. Always confirm the exact code with an OBD2 scanner before proceeding. If you’d like, I can help find the correct part numbers for factory-approved plugs and wires. Keep me updated—good luck!