BMW M235i P0300 Misfire
“It’s already had new spark plugs, coils, and injectors, but the fault keeps returning.”
That’s how Mrs T described the issue with her BMW M235i when she arrived at South Coast Garage, Eastbourne. The misfire she’d experienced appeared sporadically, causing power loss, a flickering engine light, and an irregular idling that smoothed out once the engine warmed.
For the most part, her vehicle drove well, but on cold starts or when accelerating, it became hesitant and lacked power.
Mrs T also mentioned that she’d previously taken her car to other garages, where several parts were replaced, yet the fault remained unresolved.
That’s when she turned to our expert BMW technicians at South Coast Garage, Eastbourne.
Instead of relying on guesswork, our team followed a clear, data-led repair process to identify the exact cause of the BMW M235i P0300 misfire and deliver a lasting fix and excellent value.
The Initial Evaluation: Confirming the Misfire Problem
Before any tools were touched, our BMW experts did one thing… Listened.
At South Coast Garage, Eastbourne, we took time to discuss the issue with Mrs T. She explained that her BMW M235i occasionally misfired when cold or under acceleration, triggering a flashing engine light that cleared once the car warmed up.
She added that new spark plugs, coils, and injectors had been fitted previously at another garage, but the BMW intermittent misfire hadn’t been resolved.
By understanding the vehicle’s history, including what had been attempted previously and the conditions under which the misfire occurred, our team gained a deeper insight into the issue, providing a clearer starting point for testing.
A visual inspection was then conducted to identify any obvious issues, such as oil leakage, damaged wiring, or loose connections. Everything appeared to be correct, so we proceeded to confirm the issue through testing.
A controlled test drive replicated the symptoms Mrs T described. The car hesitated briefly during acceleration, then ran smoothly once it reached temperature.
Back at our garage, we connected her M235i to our dealer-level scan tools to check for stored fault codes (if any).
The scan revealed:
- P0300 – Random or multiple cylinder misfire detected.
- P0304 – Cylinder 4 misfire detected.
- P0306 – Cylinder 6 misfire detected.
These fault codes confirmed the ECU was detecting misfires, but didn’t provide us with the underlying cause, so the next step was to dig deeper.
Finding the Source of the BMW M235i P0300 Misfire
After confirming the presence of the misfire fault, our BMW experts conducted a detailed inspection to identify the underlying cause of the intermittent misfire.
Since the hesitation occurred primarily during cold starts, our focus turned to the ignition system and recently replaced parts. Mrs T mentioned that new spark plugs, coils, and injectors had been fitted elsewhere, making them the logical place to begin and the focus of our investigation.
Upon initial inspection, everything appeared new and properly installed. But one area caught our eye, the spark plugs.
The spark plugs were non-genuine parts produced by BMW’s supplier, but they were made to slightly different specifications.
Even though the design deviation is minor, it can cause ignition irregularities in high-performance engines, such as the BMW M235i, where precise ignition timing and combustion are crucial.
To verify our suspicion, our BMW experts carried out an in-depth BMW misfire diagnosis using an oscilloscope.
Each cylinder’s ignition waveform was reviewed in detail.
Our team:
- Captured primary and secondary ignition waveforms.
- Compared the results for consistency during cold starts and under acceleration.
- Checked coil response, injector timing, and wiring integrity.
The data showed slight fluctuations in the ignition waveform but no signs of coil or injector faults. This pointed to inconsistent spark events, which are a strong indication of a spark plug problem.
Further testing confirmed that the non-genuine spark plugs were the source of the BMW M235i P0300 misfire. Although produced by BMW’s supplier, the design differences prevented perfect ignition during cold operation.
We’ve seen this fault before, and it’s covered in our spark plug blog, which explains why genuine spark plugs are key to maintaining smooth, reliable performance.
BMW M235i Misfire Repair: Getting It Right the First Time
After confirming the presence of the fault, we called Mrs T to review our findings and explain the steps required to fix the misfire.
We explained that although the spark plugs installed at another garage were produced by BMW’s supplier, they didn’t match BMW’s exact specification. This slight variation affected ignition consistency, particularly when her M235i’s engine was cold.
Our team recommended replacing all six plugs with genuine BMW components to restore optimal ignition and prevent the P0300 misfire from recurring.
At South Coast Garage, Eastbourne, we believe in open and honest communication at every stage. We keep you in the know throughout the entire repair process, and no work begins without your full approval.
Once authorised to proceed, our BMW experts carried out the repair with precision, following these steps:
- They allowed the engine to cool fully to avoid thread damage during removal.
- Removed the existing plugs and checked the plug wells and coil packs for oil or carbon build-up.
- Cleaned and prepared each plug seat for correct torque and sealing.
- Verified the electrode gap and resistance on each new spark plug.
- Installed genuine BMW plugs using manufacturer torque settings and calibrated tools.
- Reinstalled and tested the ignition coils to ensure correct performance.
This methodical approach ensured the ignition system operated exactly as BMW intended, resolving the BMW M235i P0300 misfire and restoring smooth engine performance.
Confirming the BMW M235i Misfire Was Fixed Correctly
After the repair was completed, our BMW experts set out to verify that the BMW M235i P0300 misfire had been completely resolved. At South Coast Garage, Eastbourne, every repair concludes with a validation stage that provides clear evidence the fault has been corrected.
Using the oscilloscope, our technicians rechecked the ignition system under different operating conditions. Each cylinder’s waveform was reviewed carefully to confirm steady ignition performance.
To validate these findings in real-world conditions, Mrs T’s M235i was started from cold and taken on a comprehensive road test.
The vehicle performed flawlessly throughout the drive, with all signs of hesitation and misfire gone.
A final scan revealed that all previous fault codes had cleared, confirming the successful repair.
This process verified that the BMW M235i P0300 misfire had been repaired completely, and the vehicle was performing as designed. It was now ready to be handed back to Mrs T.
BMW M235i Misfire Fixed and Performance Proven
When Mrs T came to collect her BMW M235i, our BMW technicians at South Coast Garage, Eastbourne, took the time to explain every part of the process. The oscilloscope traces, live data, and final system scans all confirmed the BMW intermittent misfire fault had been eliminated.
Through a structured and methodical diagnostic process, our team pinpointed the actual cause of the BMW M235i’s P0300 misfire and effectively repaired it, avoiding unnecessary part replacements.
Mrs T drove away knowing her BMW M235i was running perfectly once again, its smooth performance fully restored and the misfire issue resolved for good. She’d even received better than dealership value with us.
BMW M235i Misfire? Visit South Coast Garage for Expert Care
A slight hesitation, loss of power, or flashing engine light in your BMW can indicate a misfire that should be addressed promptly. Fixing the issue in a timely manner helps maintain performance and avoid costly damage to your vehicle.
At South Coast Garage, Eastbourne, our BMW experts use advanced testing and dealer-grade technical data to identify and resolve the cause of faults such as the BMW M235i P0300 misfire.
We combine technical accuracy with straightforward communication, ensuring every repair meets BMW’s exacting standards and that you stay informed throughout.
Why Drivers Choose South Coast Garage
BMW drivers across Eastbourne, Brighton, and Lewes choose South Coast Garage for professional diagnostics and dependable repairs. Here’s why:
- Experienced BMW experts.
- Transparent communication at every stage.
- 12-month parts and labour guarantee.
Join the {{review-count}} customers who’ve rated us {{average-rating}} stars on Google for trusted advice, quality repairs, and great value.
Whether your BMW has an intermittent misfire, a warning light, reduced power, or something else, our experts are here to help.
Call South Coast Garage, Eastbourne, on 01323 734473 to arrange your BMW diagnosis today.
