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Matt, Engineer
Category: Mercedes
Satisfied Customers: 20395
Experience:  Mechanical Engineer with 23 years experience in the auto industry, 8 yrs in formula 1 engine testing
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I have a vibration while driving my car cold or first start

Customer Question

i have a vibration while driving my car cold or first start up
Submitted: 3 months ago.
Category: Mercedes
Expert:  Matt replied 3 months ago.


this sounds like it may be misfiring on 1 or more cylinders, which then cease misfiring as the engine warms

So I'd begin by replacing the spark plugs if any of them fail this checklist:

You can also try spraying some water on the coil pack with the engine running. It is possible the coil is faulty and causing the misfire. If you see sparks arcing with the water, then replace the coil.

I'd check the condition of the injector plugs / connections as this could be a lean misfire if an injector isn't firing properly - the best way to check this is with a 'noid' light

Then check all the connections to the engine sensors one at a time, remove each one and examine for signs of corrosion or damage and a squirt of contact cleaner ( not WD40) will also help.

This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and leans the engine out causing rough running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas around each joint in turn. If the engine rev's up you've found your leak.

Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

Expert:  Matt replied 3 months ago.


do you still need help?

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Customer: replied 2 months ago.
The diagnosis was incorrect , it was the Transmission Mount
Expert:  Matt replied 2 months ago.

thanks for letting me know