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2000 Mazda protege with rough idling upon start up. At stops…

2000 Mazda protege with rough...
2000 Mazda protege with rough idling upon start up. At stops engine needs revving to prevent stalling but eventually dies out. Use of the scan tool did ]give any reading of trouble codes even though it worked on other cars. Fuel pump, timing, catalytic, and compression have all been checked ok.
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Answered in 12 minutes by:
3/21/2018
350matt
350matt, Engineer
Category: Mazda
Satisfied Customers: 22,919
Experience: Mechanical Engineer BEng Hons22 years experience
Verified

Hello and welcome to Just Answer

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 causing 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 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 /propaneor 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 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.

Air leaks are very temperature dependent as gaps can open up as things expand with temperature so depending on how the leak occurs ( on a hose joint with a clamp expansion will help seal and on a vacuum hose expansion ill make a leak worse) so leaks can be better or worse as the engine heats up.

1 vacuum leak path that you won't find with the above test is if the brake servo is leaking

so try clamping off servo hose to see if this has any effect

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 cleaning out the throttle body as these get clogged up with carbon and some brake cleaner washed through helps free things off.

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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Thanks Matt

350matt
350matt, Engineer
Category: Mazda
Satisfied Customers: 22,919
Experience: Mechanical Engineer BEng Hons22 years experience
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Customer reply replied 1 month ago
I appreciate your very thorough and technical diagnosis. I will follow your advice step by step and see what happens. I will notify you of our results. Too bad you dont work in vegas.

no problem

just get back to me on here

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350matt
350matt
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Category: Mazda
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