Hard start (cold)
Cranks longer when cold, then runs rough. Often fuel/air/ignition issues that show up at cold start.
MED RISK
Common symptoms
- Long crank when cold
- Runs rough for 10–30s then improves
- Fuel smell on start
- Worse in winter
Cost expectations
DIY: £0–£80. Garage: £80–£300+.
Note: prices vary by car and region. Use this as a planning range.
Most likely causes (ranked)
- Weak battery — Cold cranking amps low.
- Leaking injector — Floods cylinder overnight.
- Ignition weakness — Plugs/coils struggle when mixture is cold.
- Air leak — Leans mixture at start.
- Sensor bias — Coolant temp sensor reporting wrong temp.
Quick checks (fast, low-cost)
- Check battery voltage and crank speed.
- Smell for fuel after cold start; check oil for fuel dilution.
- Scan coolant temp reading when cold (should match ambient roughly).
- Check plugs condition and correct spec.
- Watch trims and idle stability after start.
Recommended tools
These tools make diagnosis faster and stop you buying random parts.
Related fixes
If your symptoms don’t match perfectly, check these next.
What to do next
- Start with battery and basics.
- If fuel smell is strong, treat injector leak as priority.
- If misfire codes appear on cold start, focus ignition/fuel.
AutoSolveHub helps you narrow possibilities. Always confirm critical repairs with proper testing and safe procedures.