Stalling at idle
Engine stalls at idle or when coming to a stop; often air/fuel control or vacuum related.
MEDIUM RISK
Common symptoms
- Stalls at traffic lights
- Idle drops then dies
- May restart immediately
Cost expectations
Typical costs vary by car and region. Use this as a ballpark.
- DIY / parts: £20–£80
- Garage / labour: £80–£250
Most likely causes (ranked)
Start at the top. Rule out the common, cheap causes before expensive ones.
- Vacuum leak / split hose — Unmetered air causes unstable idle and stalling.
- Dirty throttle body — Sticky throttle plate; idle control struggles.
- Faulty MAF / MAP sensor — Bad load signal = wrong fueling.
- Weak fuel pressure — Pump/filter/regulator issues show at idle/low load.
- Bad idle control valve (older cars) — Sticks or responds slowly.
Quick checks (fast, low-cost)
Fast checks you can do with basic tools before buying parts.
- Check for obvious split hoses and loose clamps.
- Clean throttle body (correct cleaner).
- Inspect MAF for contamination; log idle trims if possible.
- Listen for hissing; try a light spray test around intake (safe/controlled).
- Check fuel pressure if you have the kit.
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
- If stalling is sudden + no codes, start with vacuum/throttle cleaning.
- If trims are high, suspect air leak; if trims are low, suspect leaking injector/fueling.
- If it stalls when AC loads, check idle control and alternator output.