I have an 2000 S80 Volvo with 2.9 engine with extended warranty bought new.
At approximately 52,000 miles it has started to surge at idle.

This happens with the Air Conditioner running. I have searched the web for
surging in the Volvo but find very little. There is info on WOT surging but
mine is at idle. I am also having a hard time finding what the
specifications should be when at idle. When I first got the car I am sure
that the tach was showing 750 RPM when at idle. Currently the tach is
showing 675-700 RPM. I get very little if any surging when the air
conditioning is off. When I turn it on, the idle speed drops about 25 RPM
and it appears that the computer has been programmed with a stall indicator
at about 625 RPM thus causing the surge. This is my guess after observing
the tach and when it starts it surging. I have read that the computer is
programmed to increase the RPM to 900 whenever the air conditioning is
turned on. Being in the Alabama, the air conditioner is on all the time. I
don't have any info concerning the S80. Is this correct??

There is no Haynes manual for the S80 or any other similar publication that
I have found. Any info is limited. Even Volvo keeps the specs close to the
vest.
It makes it hard to diagnose a potential problem when you don't know the
specs or tolerances.

This car is used over 80 percent of the time for long trips usually 500 or
more miles at a time.

I just got back from a 2,000 mile trip and watched the tach and operation of
the engine/car very closely. The surging gets worse when the engine is warm
versus when it is just started and not warmed up. I also notice that when
the weather is warmer the surging is more noticeable. This may be due to
the air conditioner cycling more often. I put it on cruise and there is no
problem with hesitation going up hill and it keeps the car moving at the set
speed with little or no change in speed. Acceleration is smooth and no
hesitation is noticed.

I took the car into the dealer and he stated that it was the throttlebody
and that it needed cleaning. He stated that a software download may be
required. He also suggested as an prelude to cleaning to use a gas additive
(44K by BG Products) his suggestion. There was no change in performance
with the additive thus leading me to think that the throttle body may not be
dirty. The software download may mask the problem if it just increases the
idle speed with out correcting the true cause of the problem.
Doing a software download will be charged to me because he stated it was
a maintenance item and not covered under warranty.
However, based on my observations, I think there is a problem either with
the electronic portion of the gas pedal, air conditioner, computer or all
three.

I do not understand the relationship between the electronic gas pedal and
the throttlebody. It appears to me that the electronic connected gas pedal
should be connected to a rheostat (variable resistor) and measures the
current/resistance and then talks to the computer which then talks to the
throttle body to increase/decrease air/gas. In order to accomplish this,
the set current/resistance has to be known. If this value changes due to
wear/resistant change the computer only knows that this is the starting
value until some outside value is reach such as stall and attempts to keep
the engine going by increasing the flow of gas thus surging. However, I do
not understand why the computer does not keep the RPM at 750 if this is
indeed one of the specs for the idle speed.

I am trying to understand the problem and symptoms so that I can correct the
true cause of the problem and not search for possible causes and create
additional
problems. Is there a service bulletin that describes this problem from
Volvo? If
so could some one give me the title or number along with Volvo's corrective
action.
I would also like any information on idle speed and other related specs.
Any information concerning this will be much appreciated and
I thank you in advance.