BMW M235i P0300 Misfire
“It’s already had new injectors, coils, and spark plugs, but the misfire won’t go away.”
That’s what Mr R told our BMW experts when he arrived at RS Autotechnik, Dursley. The misfire wasn’t constant; power would drop suddenly, the engine light would flicker, then the fault would disappear.
Most of the time, the BMW M235i seemed to run fine, but under load or from a cold start, it hesitated and felt unsteady.
To add to the frustration Mr R was experiencing, he’d already replaced several parts trying to resolve the issue, but nothing worked.
That’s when he visited our BMW experts at RS Autotechnik, Dursley. Rather than replacing additional parts, we employed a precise, data-driven diagnostic process to thoroughly investigate the issue and identify the underlying cause of the misfire once and for all.
The Initial BMW Misfire Investigation
At RS Autotechnik, Dursely, our investigations begin with listening.
Our BMW experts spoke with Mr R to uncover more about the symptoms. He explained that his BMW M235i misfired when starting from a cold state or while accelerating, flashing the warning light before returning to normal.
He also mentioned that the spark plugs, coils, and injectors had been changed elsewhere, but the issue continued.
Understanding what had already been attempted and when the fault occurred allowed our technicians to prepare an accurate testing plan.
A complete visual inspection followed, checking for loose connections, wear, or contamination. No issues were found, so we moved on to confirm the fault through a controlled test drive.
During the test drive, our team experienced the issues Mr R had described; the hesitation appeared briefly under load, then cleared as the engine warmed.
Once the vehicle was back at our garage, we connected Mr R’s vehicle to our dealer-level scan equipment to look for stored codes.
We found the following fault codes:
- P0300 – Random or multiple cylinder misfire detected
- P0304 – Cylinder 4 misfire detected
- P0306 – Cylinder 6 misfire detected
These codes confirmed the misfire but didn’t reveal why it was occurring. More detailed testing would be needed to find the exact cause.
Pinpointing the Cause of the BMW M235i P0300 Misfire
With the fault confirmed, our team began investigating the misfire to find the exact cause.
Since the hesitation occurred mainly during cold starts, our technicians examined the ignition system and the new parts Mr had replaced at another garage. He’d explained that the new spark plugs, coils, and injectors had already been fitted elsewhere, so that was our first area to check.
At first glance, everything looked to be in order; the new parts were new and had been installed correctly. However, the spark plugs quickly caught our attention. They were non-genuine items made by BMW’s supplier but produced to slightly different tolerances.
Even these minor design differences can influence combustion performance in engines like the BMW M235i, where accuracy and timing are critical.
To verify our suspicion, our experts carried out a BMW misfire diagnosis using an oscilloscope.
Each cylinder’s ignition waveform was reviewed carefully. Our team did the following:
- Recorded both primary and secondary ignition traces.
- Compared readings across all cylinders under load and cold start conditions.
- Checked coil operation, injector performance, and wiring signals.
The data revealed irregularities in the ignition waveform, with no consistent pattern; this ruled out coil and injector faults, pointing directly to inconsistent spark formation – a strong indication of a spark plug fault.
Our findings confirmed that the non-genuine spark plugs were the cause of the BMW M235i’s P0300 misfire. While made by BMW’s supplier, they didn’t match BMW’s exact specification, causing ignition instability during cold operation.
Repairing the BMW M235i Misfire
Once the fault was identified, our BMW experts called Mr R to review our findings and to offer our recommendations.
We explained that although BMW’s supplier had produced his vehicle’s new spark plugs, they didn’t meet BMW’s precise design specification. This subtle variation caused unstable ignition, particularly during cold starts.
Our recommendation was to replace all six spark plugs with genuine BMW components, ensuring proper combustion and long-term reliability.
At RS Autotechnik, Dursley, we believe in complete transparency. No repair begins without your approval, and every step is explained clearly from start to finish. You’re always in complete control with us.
Once Mr R gave us the go-ahead, our experts completed the work following BMW’s exact repair procedure. Here are some of the steps taken:
- Allowed the engine to cool fully before plug removal to prevent thread damage.
- Removed the spark plugs and inspected the coil packs and plug wells for contamination or carbon build-up.
- Cleaned and prepared each plug seat for accurate torque and sealing.
- Checked electrode gap and resistance on each new plug prior to installation.
- Installed the genuine BMW spark plugs to BMW’s specified torque using calibrated tools.
- Re-fitted and tested the coils to ensure correct operation.
This thorough process ensured the ignition system performed exactly as BMW designed, permanently resolving the BMW M235i P0300 misfire.
Ensuring the BMW M235i Misfire Was Fixed
Once the repair was complete, our BMW experts at RS Autotechnik, Dursley, performed a detailed validation to confirm the misfire had been eliminated. Each completed repair undergoes this stage to provide clear proof that the fault has been resolved.
Using the oscilloscope, our technicians rechecked the ignition system under different conditions. Each cylinder’s ignition waveform was examined to confirm stable and consistent performance.
To verify these results on the road, the BMW M235i was started from cold and taken on a comprehensive test drive.
Throughout the test drive, the BMW’s engine performed smoothly. The hesitation that had once appeared under acceleration was gone, and the intermittent misfire did not return, suggesting that the BMW intermittent misfire had been solved.
To double-check, a final diagnostic scan confirmed that no codes were present, verifying that the BMW M235i P0300 misfire had been repaired successfully.
This part of the process confirmed that the repair was complete and that Mr R’s car was performing exactly as BMW intended, ready to be handed back.
A Proven BMW Misfire Repair
When Mr R came to collect his BMW M235i, our BMW experts walked him through every step of the diagnostic and repair process. Using detailed oscilloscope traces, test data, and final diagnostic scans, we confirmed that the misfire had been completely resolved.
Through a clear, data-led diagnostic process, our team identified and corrected the BMW M235i P0300 misfire, delivering a precise and lasting solution.
Mr R left certain that his BMW M235i was running exactly as it should, with smooth, consistent performance restored and the fault fully resolved.
BMW M235i Misfire? Book an Inspection with RS Autotechnik
If your BMW 2 Series feels uneven, loses power, or triggers the engine light, it could be an early sign of a misfire. Getting it checked promptly can prevent further complications and expensive repairs.
At RS Autotechnik, Dursley, our BMW technicians use dealership-level equipment and official BMW technical information to locate and repair faults such as the BMW M235i P0300 misfire.
You’ll receive the same technical accuracy as a BMW main dealer, combined with the honesty and personal service of a trusted local garage.
Why BMW Drivers Choose RS Autotechnik
BMW owners across Dursley, Bristol, Tetbury and the surrounding areas choose RS Autotechnik for expert diagnosis and reliable repairs. Here are a few other reasons why:
- BMW experts.
- Friendly, transparent customer service.
- 12-month parts and labour guarantee.
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Whether your BMW is experiencing an intermittent misfire, displaying a warning light, or showing reduced performance, our team can help.
Call RS Autotechnik, Dursley, on 01453 796345 to book your expert BMW misfire diagnosis today.
