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Discussion Starter #1
My son has a 135 multi-air and idle is about 700rpm. Whilst it is not and obvious judder, to me it feels like it has a misfire at idle or the idle is too low and therefore makes the engine vibrate but it is a very small amount.

I'm sure a lot of people wouldn't notice but I am sensitive to mechanical issues and a competent mechanic. I see lots of threads that this could be early signs of multi-air failure but this car had a new unit fitted about 4,000 miles ago.

The car has about 60,000 miles on it but no real service history.

Today I have checked and changed the spark plugs (looked like they were original) and checked for oil in the plug recesses but no oil there.

I removed the multi-air filter (the one that needs a 10mm allen key) on the front of the cylinder head and cleaned that but it wasn't dirty so no problem there.

I have spotted that the O ring on top of the cam cover that the air re-circulation control has a very small weep of oil so that will need replacing.

When driving the car pulls like a train, especially in D, so I don't think there is a major problem.

Questions are:-

What is normal idle speed for a 135 multi-air?
Is there anything else to check that might be causing this low rpm and very slightly lumpy idle?
Where are the MAF or MAP sensors on this engine as I think a clean of those might help?
The air filter is clean and relatively new, so not a problem there.
 

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Discussion Starter #3
JnL - fantastic, thank you.

Do you know what the normal idle speed of this engine is? Any thoughts on what may be causing the low idle / small judder?
 

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I had problems during idling when the membrane inside the oil separator had a leakage.
It is in the black plastic box just left of the MAP sensor.
 

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Discussion Starter #5
JnL. Thanks again. Is there anything obvious to look for to see the damaged membrane or way to test it? I know the seperator that you mention 3x M10 bolts and a hose clip lets it be removed.
 

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Just visual inspection is enough. I had a small crack in it and so the sealing function had not been guaranteed anymore.
Mine (although 170HP) runs around 800 rpm in idle btw. So I think 700 is also fine.
 

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Discussion Starter #7
Thank you JnL. It seems not so many mechanically minded people on the newer car forums here. I have had Sud, 75, 33, 164, 147, 156, 159, Giulietta, Alfetta GTV and now my son's Mito. Had I asked on the 147 forum or other forum I would have been inundated with suggestions.

Thanks again, you have been very helpful.
 
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