BMW M235i P0300 Misfire
“It’s had new spark plugs, coils, and injectors, but the misfire keeps returning.”
That’s what Mrs A said to our technicians when she brought her BMW M235i to JDK Automotive, Camberley.
Her vehicle had a troubling misfire issue would appear unexpectedly, causing a brief loss of power and a flickering engine light before everything returned to normal.
The car ran smoothly for most journeys, but from a cold start or when accelerating, it felt sluggish and hesitant, which is the last thing you expect from a BMW.
Before coming to us, Mrs A had already tried several garages, but despite multiple part replacements, the misfire persisted.
At JDK Automotive, Camberley, our BMW experts take a structured, evidence-based approach to all repairs. Using manufacturer-level diagnostic tools and technical data, we set out to uncover the real cause of the misfire and permanently resolve the issue.
Our Initial Evaluation: Listening Comes First
At JDK Automotive, Camberley, every diagnosis begins with a conversation.
When Mrs A brought in her BMW M235i, we asked her to describe the fault in her own words. She told us the misfire appeared mainly during cold starts and when accelerating, with the engine light flashing briefly before clearing as the car warmed up.
She’d already replaced the coils, spark plugs, and injectors at another garage, but the fault persisted.
By listening carefully to that history, our BMW technicians could form a clear plan before touching a tool.
We began with a visual inspection to check for damage, contamination, or loose connectors; everything appeared to be fine. The next step was to see if we could reproduce the fault.
To do so, a controlled test drive was performed. The misfire occurred at the start, while the engine was cold, and during acceleration. However, things smoothed out once the engine reached its operating temperature.
Back at our garage, our team of experts connected our dealership-level scan tool to Mrs A’s BMW to check for any stored fault codes.
The check revealed the following:
- P0300 – Multiple cylinder misfire detected.
- P0304 – Cylinder 4 misfire detected.
- P0306 – Cylinder 6 misfire detected.
These fault codes confirmed that the ECU recognised the misfires but couldn’t identify the cause. Fault codes highlight the symptoms, but not the reason behind them.
To pinpoint the real cause, we needed to conduct further testing.
Locating the Real Cause of the BMW M235i P0300 Misfire
Now that the fault had been verified, our BMW experts at JDK Automotive, Camberley, moved on to uncover what was truly behind the BMW M235i’s intermittent misfire.
Because the hesitation and misfiring only occurred when the car was cold, our team focused on the ignition system and recently replaced the parts. Mrs A told us that new spark plugs, coils, and injectors had already been fitted at another garage, so that was where we began.
At first, everything looked new and properly installed, but the spark plugs caught our attention.
The spark plugs were non-genuine parts. While BMW’s supplier had manufactured them, they had slightly different tolerances.
Even small design changes can significantly impact performance in high-output engines like the BMW M235i, where ignition timing and combustion stability are crucial.
To confirm our suspicion, we performed a detailed oscilloscope analysis of the ignition system.
Each cylinder was tested carefully to spot any inconsistencies:
- Our team captured primary and secondary ignition waveforms across all cylinders.
- Compared the traces during cold starts and under acceleration.
- Checked the operation of coils, injectors, and wiring.
The results showed inconsistent readings across the ignition signal, but with no real pattern or consistency. This eliminated any suspicion we had for the coils or injectors and highlighted spark plug irregularities as the likely cause of the BMW intermittent misfire issue.
Our testing confirmed that the non-genuine spark plugs were the cause of the BMW M235i P0300 misfire. Although made by BMW’s supplier, they didn’t match BMW’s specification, leading to ignition issues when cold.
We’ve encountered this problem before, and it’s covered in detail in our spark plug blog, where we discuss why using the correct spark plugs is essential for reliability and consistent performance.
BMW M235i P0300 Misfire: A Reliable Repair
Once the diagnosis was confirmed, our BMW experts at JDK Automotive reviewed the results with Mrs A before continuing with the repair.
We explained that although BMW’s supplier made the spark plugs fit elsewhere, they did not meet BMW’s exact engineering standards. Small variations in design were enough to cause weak ignition and cold-start misfires.
Our recommendation was clear: replace all six plugs with genuine BMW parts to ensure optimal combustion and long-term reliability.
At JDK Automotive,Camberley, we prioritise communication and transparency. Every repair is explained clearly, and no work takes place until approved. You’re always in full control from the beginning.
Once Mrs A gave us the go-ahead, our technicians carried out the replacement process step by step:
- Allowed the engine to cool completely before starting.
- Removed the old plugs and inspected the coil packs for carbon or oil residue.
- Cleaned the threads and plug seats for a precise fit.
- Checked each new plug’s gap and resistance before installation.
- Installed the spark plugs according to BMW torque recommendations, using calibrated tools.
- Re-fitted coils and confirmed they were operating optimally.
This detailed process ensured the ignition system operated exactly as BMW designed it, resolving the fault and restoring full, smooth performance to Mrs A’s BMW M235i.
Confirming the BMW M235i Misfire Was Repaired
With the repair complete, our BMW experts at JDK Automotive, Camberley, performed a final round of validation to confirm that the BMW M235i P0300 misfire was fully resolved.
Each repair concludes with this stage to provide clear proof that the fault has been adequately repaired.
Using the oscilloscope, we rechecked the ignition system under different driving and temperature conditions. Each cylinder’s ignition waveform was examined carefully for accuracy and stability.
To verify this in real-life conditions, the car was started from cold and taken on a comprehensive road test around Camberley and nearby routes.
During the test, the BMW’s engine performed faultlessly. The hesitation that had previously appeared during acceleration was gone, and the misfire didn’t recur.
A final diagnostic scan confirmed that no fault codes remained, verifying that the BMW M235i P0300 misfire had been completely fixed.
This last stage provided the final confirmation that the engine was running exactly as BMW intended.
Result: Proven BMW Misfire Repair and Lasting Confidence
When Mrs A collected her BMW M235i, our experts explained every step of the diagnostic and repair process. We showed her the oscilloscope readings, fault code reports, and that final scan confirmed the issue had been completely resolved.
By following a clear, evidence-driven diagnostic process, our BMW technicians at JDK Automotive, Camberley, repaired the BMW M235i P0300 misfire quickly and accurately, avoiding unnecessary part replacements.
Mrs A left with full confidence, knowing her BMW M235i was running exactly as it should and that the misfire fault had been solved.
BMW M235i Misfire? Get It Checked At JDK Automotive
If your BMW 2 Series loses power, hesitates, misfires, or flashes the engine warning light, it’s a sign to have it checked immediately.
Even a minor misfire can turn into a costly repair if left unresolved.
At JDK Automotive, Camberley, our BMW experts utilise advanced diagnostic systems and technical data to pinpoint the root cause of faults, such as the BMW M235i P0300 misfire.
We match BMW dealer-level diagnostic precision with the trusted, customer-first approach of an independent garage. You’ll always receive transparent updates and professional recommendations before any work begins, keeping you in total control.
Why Drivers Choose JDK Automotive
BMW owners across Camberley, Farnborough, and surrounding areas choose us for precision diagnostics and reliable repairs.
With our garage, you get:
- Expert BMW technicians.
- Transparent communication.
- 12-month parts and labour guarantee.
Join the {{review-count}} customers who’ve rated us {{average-rating}} stars on Google for trusted service, knowledge, and value.
Whether your BMW 235i is experiencing a misfire, warning light, or performance issue, our technicians can diagnose and repair it efficiently.
Call JDK Automotive, Camberley, on 01276 535585 to schedule your BMW check-up today.
