2001 S80 - At idle w/o AC the engine rpm repeatedly drops to approx. 500 then surges to 1200. If lights are ON the lights dim at rpm decrease and return to normal at surge. If AC is under load the surge does not occur. If the engine is under only slight load, as at very low throttle position and creep speed, the surge does not occur. Blipping the throttle is useful to avoid undesired surge when leaving stopped position - as at trafic light.
Thanks.
You could have a bad or contaminated Mass Air Flow (MAF) sensor. You can get a used one online for less then 100. You can also purchase a can of MAF sensor cleaner at a local auto supplies store and clean it. It located right at the air filter housing.
Most likely the surging is due to a contaminated electronic throttle module (etm). If it is the throttle module Volvo has a 10 year 200,000 mile extended warranty that could cover the problem.
There is also the chance that there is a vacuum line loose and/or leaking. I would take it to the dealer and for a nominal fee they can diagnose the problem.
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