The engine produces more symptoms than any other system, and it is also the one where guessing gets expensive fastest. Misfires, rough idling, knocking, oil consumption and power loss all have short lists of realistic causes once you know when the symptom appears.
What Usually Goes Wrong
Misfires and rough running
Uneven idle, flashing check engine light, a stumble under load. Usually ignition, fuel delivery or a vacuum leak — in that order of likelihood.
Knocking and ticking
Timing-related ticking, lifter noise, pre-ignition knock under load and the deeper bottom-end knock that means stop driving.
Oil consumption and leaks
Where the oil is actually going: valve stem seals, piston rings, PCV faults, and the gasket leaks that only show up when hot.
Starting and stalling
Cranks but won’t fire, starts then dies, stalls at junctions — fuel pressure, crank sensors, idle control and immobiliser faults.
Guides in This Section
All engine guides ›-
How to Find a Vacuum Leak: Simple Checks and Smoke Test
Find a vacuum leak step by step: free hose checks, fuel trim at idle vs 2,500 rpm, a vacuum gauge and the…
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How to Tell If an Ignition Coil Is Failing
A failing ignition coil usually shows up as a misfire on a single cylinder. Here’s how to recognise the symptoms, swap-test the…
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How to Clean a Dirty Throttle Body (When It’s Worth It)
Carbon around the throttle plate can cause a rough, hunting or stalling idle. Here’s when cleaning is worth doing, how to do…
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How to Tell If Your Fuel Filter Needs Replacing
A clogged fuel filter starves the engine under load. Whether it’s a cheap in-line part or a sealed in-tank unit depends on…
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Rattling Noise on Cold Start That Goes Away
A rattle that appears only when the engine is cold and fades within seconds can be normal — or the first warning…
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Car Smells Like Burning Oil
A hot, acrid oil smell almost always means oil is reaching the exhaust or engine block. Here’s how to find the source…
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Smoke Coming From Under the Hood (Steam vs Smoke)
Not everything rising from under the hood is dangerous, but some of it is. Here’s how to tell coolant steam from burning…
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Engine RPM Surges Up and Down at a Steady Speed
When revs rise and fall while your foot is steady, the engine or transmission is changing something it shouldn’t. Here’s how to…
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Car Idles Too High (Revs Stay Above 1,000 RPM)
A warm engine that idles well above its normal speed is usually drawing in extra air or has been told it’s cold.…
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Car Stalls While Driving (Engine Cuts Out at Speed)
An engine that cuts out at speed is a different problem from one that dies at idle: fuel, spark and sensor faults…
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P0012 Code: Intake Camshaft Timing Over-Retarded (Bank 1)
P0012 means the intake camshaft is lagging behind where the computer wants it. Low or dirty oil and a sticky VVT solenoid…
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P0441 Code: EVAP System Incorrect Purge Flow
P0441 means fuel vapor isn’t flowing the way the computer commands during purge. A stuck purge valve or blocked line is the…
Chock the wheels, use axle stands rather than a jack alone, let hot components cool, and disconnect the battery before touching wiring. Brakes, steering, fuel lines, airbags and the orange high-voltage cabling on hybrids and EVs can cause serious injury or death if handled incorrectly. If a job is beyond your tools or experience, stop and book a qualified mechanic — there is no shame in it and it is always cheaper than the alternative.