A judder, kangaroo-hop or hesitation when you press the throttle almost always points to a misfire — one cylinder isn't producing its share of power, so the engine shakes as it pulses unevenly.
Top 6 UK causes
1. **Failing coil pack or spark plug** — most common on petrol cars over 60,000 miles. Listen for a "fluttering" idle. 2. **Dirty or failing fuel injector** — common on direct-injection petrols (VW TSI, Ford EcoBoost) and all diesels. 3. **Blocked DPF or EGR valve** (diesels) — judder often happens between 1,500–2,500 rpm. 4. **Failing mass airflow (MAF) sensor** — judder worst when warm. 5. **Vacuum leak** — split intake hose or perished gasket. 6. **Dual-mass flywheel** — judder felt through the clutch pedal on pull-away.
How to narrow it down
- Engine management light on? Get codes read first (£20–£45) - Judder only under load? Coil pack or injector - Judder at idle too? Misfire — check plugs/coils - Judder with clutch slip? Dual-mass flywheel - Diesel with black smoke? EGR or DPF
Typical UK costs
- Spark plugs (set of 4): £80–£160 fitted - Coil pack: £80–£200 each fitted - Petrol injector clean: £90–£180 - Diesel injector replacement: £250–£500 each - EGR clean: £180–£350 - Dual-mass flywheel + clutch: £900–£1,800
Is it safe to keep driving? — Short journeys yes, but a long-running misfire can damage your catalytic converter (£600+ to replace). Get it diagnosed within a week.
Could it be the fuel? — Occasionally. Bad fuel from a contaminated forecourt can cause a temporary judder that clears after 1–2 tanks of fresh fuel.
Bob's Mechanical Repairs — independent family-run garage in Birnam, Dunkeld, Perthshire. Call 01350 727 276 or email bob@bobsmechanicalrepairs.co.uk.