Loss of engine power: common causes

Loss of power shows as sluggish acceleration, difficulty revving or holding speed on hills. Causes vary from the simplest (clogged air filter) to the most expensive (turbo, catalyst). Here are the most common causes.

Air filter and intake

A very dirty air filter limits airflow and the engine “suffocates”. Replacement is simple and cheap (€15–50). An air leak after the mass air flow sensor (detached hose, crack) can skew injection calculation and cause lack of power or hesitation. A clogged or stuck EGR valve (especially diesel) reduces performance and can trigger the check engine light.

Turbo and exhaust

On turbo engines, loss of power can come from a faulty turbo (wear, oil leak, stuck variable geometry), a boost hose holed or detached, or a wastegate fault. A clogged catalyst or particulate filter (DPF) restricts exhaust flow and chokes the engine; the vehicle lacks response and may go into limp mode.

Injection and ignition

Clogged or faulty injectors (petrol or diesel) give incomplete combustion and loss of power. On petrol, worn spark plugs or ignition coils can cause misfires and reduced performance. An electronic diagnostic (fault code read) and pressure checks (turbo, injection) help pinpoint the cause.

What to do in practice

Do not push an engine that lacks power: a struggling turbo or DPF can get worse. Have the vehicle checked (diagnostic, air filter, hoses, turbo, exhaust). Depending on cause, costs range from a simple filter change (tens of euros) to turbo replacement (€1,000–2,500 and more) or DPF (€800–2,000). My Auto Check-up helps you prepare your visit by gathering useful information for an initial cost estimate.