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Hi all,

Sorry if this has been discussed already, couldn't find anything on this ongoing issue.

Alfa GT Blackline, 57 plate, 55k

So, the engine won't idle properly and fluctuates between 900-1100 rpm and then stalls on occasion. I also intermittently get a sudden judder or loss of power (literally about 1 second) it's hard to explain, if it happens when I am pulling away it looks like I can't drive properly, or if driving along the rev counter momentarily drops and you feel the loss then the power comes back.

The garage thought it was a split in the air intake but that didn't work, the throttle body has also been cleaned, I could do with any advice as it is really a small but completely annoying fault.

Thanks all:rotate:
 

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I had a similar issue with a previous car,turned out to be the crankcase ventilation system valve.
And yes,you can get stored codes without an eml.
 

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Assuming they fitted a good quality MAF, then it is probably not that.

Still, car could have some codes.

Might be a coil pack if it happens once the car has warmed up and you are putting a load on, up hill or starting off. Usually that would make the car run rough though. I've had 4 cylinder cars run on only 1 cylinders momentarily as I was trying to diagnose a coil pack issue.

Could be oil in the spark plug wells, TS can be prone to that when people top up the oil. Check the plugs near the filler cap I would think first.
 

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As above.
Check cam cover gasket and ensure spark plug wells are dry.
Disconnect breather and block return to throttle body to test.
Clean earth on cylinder head and engine ECM mounting plate.
MAF sensor should return 1.5-4.5 volts (15kg/hr warm idle to 400+kg/hr full throttle 6400rpm).

If that doesn't sort it then oscilloscope analysis of crank sensor wave form or trying another Bosch sensor (as they are quite cheap) should be next. A defective coil should log a fault code. Generally the TS is quite straightforward and reliable.

A check of induction hose and throttle body clean was wise.
 

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While oil in the wells is not a good thing, I can't see it causing a misfiring plug (high voltage travelling to earth via the oil rather than via the plug gap). Because oil is a very good insulator it is often used as a cooling medium for high voltage applications, where the electrical gubbins are submerged and in direct contact with the 'coolant'. I've had plugs that were more or less submerged in oil, and only found by chance, with no misfires.

Water on the other hand will easily cause a misfiring plug, if there is enough of it in the well (perhaps with oil floating on top?).

Rehgards,
John.
 
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