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If the engine shakes at idle but runs well when driving, there are two typical causes: worn engine mounts or one cylinder working less than the others. Telling them apart is simple by reading the corrections per cylinder.

How to tell which of the two

• Engine mounts: vibration at idle that increases with the air conditioning on or when a gear is engaged, but a smooth engine under acceleration
• Irregular cylinder: vibration accompanied by slight jerking, rising consumption or the engine light

Most common causes

• Collapsed hydraulic engine mounts
• Injector with flow out of tolerance
• Worn spark plugs or coils (petrol)
• Dirty EGR making the idle rough
• Encrusted throttle body
• Intake leaks
• Low compression in one cylinder

What to do right away

• Try switching the air conditioning on and off: if the vibration changes a lot, suspect the mounts
• Have the injection corrections per cylinder read: they identify the injector responsible
• If the idle is only rough when cold, mention it: it is a useful diagnostic clue

How MasterTuning helps

We do not replace parts by trial and error: we read the real values from the ECU (pressures, flow rates, corrections, temperatures) and identify the component responsible. Then we repair and recalibrate the software where needed. Centres throughout Italy.

Read more: vehicle database · what is ECU remapping · find an installer

Does your car have this symptom? Book a diagnosis at your nearest MasterTuning centre.

Frequently asked questions

Why does the engine only vibrate with the air conditioning on?

The compressor increases the load at idle: if the engine mounts are worn, the vibration becomes obvious.

Can vibration at idle be caused by the injectors?

Yes: an injector out of tolerance makes combustion in that cylinder irregular, especially at idle.

Does cleaning the EGR fix a rough idle?

It can, if the valve is encrusted and not closing properly, but it should be checked with a diagnosis first.