200 10V stumbles, poor mileage

[Konstantine Bogach]

Hi Huw,
forgot to mention O2 sensor:  it is only one year old, maybe two.   
But... who knows, you are right, that would be an explanation.  I 
checked duty cycle and it sweeps around 50% - same as it was before the 
car started to stumble.   Would it be a proof of good oxygen sensor?
Can I disconnect oxygen sensor connector when measuring?  Would using a 
scope give more definite test?

Thanks a lot.
Konstantine


On 12/19/2009 05:49 PM, Huw Powell wrote:
> A failed oxygen sensor could cause such symptoms.  Put a voltmeter on 
> its output at warm idle, while connected, and check what it's doing.
>
> Konstantine Bogach wrote:
>> Hi all,
>>
>> my 200 MC2 stumbles at idle or when I increase RPM, until I am at 
>> 3000 rpm.  Above 3K I don't feel stumbling.  All plugs are same wet 
>> and black. Coil resistance,  CIS system and control pressure are 
>> within the spec.  Can not see a vacuum leak anywhere (also did carb 
>> cleaner spray test).  But I don't think it is a leak b/c at higher 
>> boost it runs better rather than worse.  Inspection of ignition 
>> distributor cap did not reveal a clue (I tried the spare one too.)
>>   Almost not working in cars last 2 years I forgot what I had learnt 
>> before (mostly from this list).  What I should be looking next?  Can 
>> broken soldering in the throttle switch cause such symptoms ?  Hall 
>> sensor?  RPM or crank position sensor?  There is no codes stored.
>>
>> All ideas will be appreciated.
>> Thank you.
>> Konstantine
>> 200 '91 & UrS4 '93.
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>