# Engine problems

Every engine symptom we cover, with its most common cause and how urgent it is.

## 15 engine symptoms

| Symptom | Most common cause | Verdict |
| --- | --- | --- |
| [Why is blue smoke coming from my exhaust?](/symptoms/blue-smoke-from-exhaust) | Clogged or stuck PCV valve | Drive to a shop this week |
| [Why does my car smell like something is burning?](/symptoms/burning-smell-from-car) | Oil leaking onto the exhaust (burnt oil smell) | Drive to a shop this week |
| [Why does my car crank but not start?](/symptoms/car-cranks-but-wont-start) | No fuel delivery (fuel pump, fuse or relay) | Drive to a shop this week |
| [Why does my car hesitate when I accelerate?](/symptoms/car-hesitates-when-accelerating) | Worn spark plugs or failing ignition coils | Drive to a shop this week |
| [Why does my car jerk when I accelerate?](/symptoms/car-jerks-when-accelerating) | Misfire from worn spark plugs or ignition coils | Drive to a shop this week |
| [Why is my car leaking oil?](/symptoms/car-leaking-oil) | Leaking valve cover gasket | Drive to a shop this week |
| [Why does my car lose power when accelerating?](/symptoms/car-loses-power-when-accelerating) | Misfire from worn spark plugs or a failing coil | Drive to a shop this week |
| [Why does my car shake at idle?](/symptoms/car-shakes-at-idle) | Misfire from worn spark plugs or a weak ignition coil | Drive to a shop this week |
| [Why does my car shake when I accelerate?](/symptoms/car-shakes-when-accelerating) | Worn inner CV joint or damaged axle | Drive to a shop this week |
| [Why does my car smell like gas?](/symptoms/car-smells-like-gas) | Loose, damaged or missing gas cap | Stop driving |
| [Why does my car stall while driving?](/symptoms/car-stalls-while-driving) | Failing crankshaft position sensor | Stop driving |
| [Why is my engine knocking?](/symptoms/engine-knocking-noise) | Spark knock (pinging) from fuel igniting too early | Drive to a shop this week |
| [Why is my car getting bad gas mileage?](/symptoms/poor-gas-mileage) | Underinflated tires | Safe to drive |
| [Why is my car idling rough?](/symptoms/rough-idle) | Worn spark plugs or a failing ignition coil | Drive to a shop this week |
| [Why does my car squeal when I start it?](/symptoms/squealing-noise-when-starting) | Worn, glazed or stretched serpentine belt | Drive to a shop this week |

## Other symptom groups

- [Exhaust and smoke](https://diagxcar.com/symptoms/exhaust)
- [Brakes](https://diagxcar.com/symptoms/brakes)
- [Battery, starting and electrical](https://diagxcar.com/symptoms/electrical)
- [Cooling and overheating](https://diagxcar.com/symptoms/cooling)
- [Transmission](https://diagxcar.com/symptoms/transmission)
- [Steering and suspension](https://diagxcar.com/symptoms/steering)
- [Tires and wheels](https://diagxcar.com/symptoms/tires)

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Source page: https://diagxcar.com/symptoms/engine
General information, not a substitute for a qualified mechanic.