Author Topic: How to lower engine idle speed for MOT.  (Read 813 times)

Offline Jasikasisback

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How to lower engine idle speed for MOT.
« on: 17 November 2017, 19:12 »
Hey everyone,

As you can guess, my car failed emissions due to exhaust engine idle speed being too high

The tester said I can bring the car back for a re-test.

Most likely the idle control valve is damaged as I often have to give light acceleration when starting in the morning or it will just die on me..not always but a lot of the time.

The rest of emissions were fine and if I can get the idle speed down, then the car will pass.

My question is should I take the car in the night before and let them test the idle speed when the car is cold, or should I take the car for a  blast down the motorway and bring it in for testing without shutting off the engine to get the idle speed down within normal limits.

Any advice would be greatly appreciated. Thanks in advance.

The car is not VW....it is 1997 Toyota Previa...(don't shoot me for that...had three VW's in the past so...)

Offline itavaltalainen

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Re: How to lower engine idle speed for MOT.
« Reply #1 on: 18 November 2017, 09:57 »
High idle is usually to do with excessive air - i.e. a leak somewhere.
If it is the idle control valve, what type is it? Might be worth dismantling and cleaning, then put back on. Drive for a short while and see if that brings it down?
Could also be a temperature issue, i.e. temp sender telling the ECU it's really cold and the engine increases idle speed.
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Offline Jasikasisback

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Re: How to lower engine idle speed for MOT.
« Reply #2 on: 21 November 2017, 10:07 »
I'll give it a go today...most likely the valve is dirty and sticks so will clean the throttle body and the valve as best as I can. It runs fine when at temperature so the valve most likely is still working...seen a link on youtube on how to clean it without actually removing it and people have tried it with good results...should work for me...I am loathe to take things more apart than necessary as my luck I usually strip the bolts or something else bad happens...primum non nocere is my motto...