misfire under light load

[Mike Miller]

Quite true, Bernie - I went back and re read the OP.  Missed the part 
about the cold engine working fine.

I would say check the Intake Air Temp sensor.

I would still use the timing light to see if it can be isolated to a 
specific cylinder or if all cylinders randomly and I would do that with 
both a cold and a warm engine. Things do expand when they get warm.

No explanation why the moisture from rains would lessen the issue.

--mike

On 11/12/2011 6:34 PM, Bernie Benz wrote:
> 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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