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2006 Smart fortwo CDI I have changed the glow plugs and fuel

Customer Question
2006 Smart fortwo CDI...
2006 Smart fortwo CDI I have changed the glow plugs and fuel filter. used injector cleaner as well. Starts hard when its warm. Idle surges up\dwn from 1000 to 700 rpm. Runs great on the highway.. I drive 120K on the highway
JA: Is the fuel filter an external one, or is it inside the tank?
Customer: external
JA: Are you fixing your Fortwo yourself? What have you tried so far?
Customer: myself. I changed the fuel filter and glow plugs
JA: Anything else you want the mechanic to know before I connect you?
Customer: no
Submitted: 11 months ago.Category: Mercedes
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Answered in 3 hours by:
12/16/2016
Mercedes Mechanic: Matt, Engineer replied 11 months ago
Matt
Matt, Engineer
Category: Mercedes
Satisfied Customers: 22,152
Experience: Mechanical Engineer with 23 years experience in the auto industry, 8 yrs in formula 1 engine testing
Verified

Hello

This could be an airleak after the airflow meter, anyair dragged in here isn't 'seen' by the ECU and so not compensated for and canlean the engine out and can also allow the engine to rev up when not desiredcausing rough running.

As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hoseclips 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/propane or brake cleaner around each joint in turn. If the engine rev's up you've found your leak.

Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.

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 oflighter gas to provide a spraying 'wand' and allow a direct blast of gas intoeach area, especially those difficult to reach with large implements.

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.

if the engine condition is the same then chances are the meter or the connection to it is faulty

It’s also worth cleaning the MAF sensor wires, as they can get coated with dirt over time which then offsets the reading

Use some contact cleaner or brake cleaner to spray onto the wires to remove the dirt – on no account touch the wires with anything as they are very fragile

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Mercedes Mechanic: Matt, Engineer replied 11 months ago

Hi

do you still need help?

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Matt, Engineer
Category: Mercedes
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Experience: Mechanical Engineer with 23 years experience in the auto industry, 8 yrs in formula 1 engine testing

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