misfire under light load

[Bernie Benz]

Mike, IMO most of the possibilities that you suggest would cause more  
of a problem under heavy throttle, high boost than they would at  
idle, which is not the case.

Bernie

On Nov 12, 2011, at 5:06 PM, Mike Miller wrote:

> Check spark plug wires. Make sure no insulation cracks allowing a  
> short to ground. Try revving the engne at night when you can see if  
> any plug wires are "leaking".
>
> You might also try an inductive timing light - put it on each wire  
> and see which cylinder is not firing - that's likely the easiest  
> way to isolate IF you have access to the timing light. I found a  
> totally dead wire that way. Make sure the wires are all seated on  
> both ends.
>
> Could also be the coil wire not seated or arcing under load.
>
> --mike
>
> On 11/12/2011 5:34 PM, Bernie Benz wrote:
>> If no obvious leakage tracks on cap or rotor I would not expect a  
>> problem there. And no problem under heavy throttle. I’d start by  
>> looking at injectors, maybe one is sluggish to open.
>>
>> Bernie
>>
>> On Nov 12, 2011, at 3:01 PM, 200q 20v wrote:
>>
>>> Fellow experts,
>>>
>>> Driving in 4th gear, 2000 rpm, increasing throttle feels like a
>>> misfire in several cylinders. E.g. virtually no power.
>>> It is not very pronounced when engine is cold.
>>> It appeared to start after last track event. Leaving the track I
>>> noticed slightly rough idle and above mentioned misfire while  
>>> driving
>>> home.
>>> Changed several years old spark plugs (found the cheapest F5DPOR  
>>> on Amazon).
>>> Virtually no changes. There are no vacuum leaks (cold engine pulls
>>> full boost with no problems) no codes in ECU.
>>> Strangely enough during recent heavy rain misfires were much less  
>>> pronounced.
>>>
>>> If left on idle a few misfires a minute can be heard.
>>>
>>> Wires and distributor cap are about 5 years old, much less then
>>> average miles per year.
>>>
>>> I wonder if anyone has any ideas. I plan to look at replacing  
>>> cap / rotor next.
>>>
>>> Eugene.
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>>> 200q20v
>>
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>
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