Hey, first time poster here.
My 1998 S70 GLT with about 91k miles has a very strange idle and I have no explanation for it.
While idling (Park or Neutral it doesn't matter) the revs' will suddenly drop for a second, then will go back to idle. When this happens I'm usually not looking and only notice it when the engine shudders so I don't know how much the revs drop but it can't
be more than 150 rpm. It's very infrequent, so infrequent in fact that my dealer couldn't replicate it to figure out what it was, and not 5 minutes after I got the car back, it happened TWICE.[sm=headbang.gif] Strangely though it seems to happen much more when I have the A/C on.
My dad thinks its the fuel/air mixture making the engine more fuel efficient while sitting, and the engine is just hiccuping, but I don't know. If anyone can tell me what the problem might be and how to fix it would be amazing.

Thanks

 

Has the throttle and idle motor been cleaned?

 

Not that I'm aware of, I've only had the car since December 2007 and if I'm honest I'm not a wiz with cars, yet, so any suggestions would be greatly appreciated and I could talk about them with my dad
or the dealer to figure out what's wrong. It could be what you said. to maybe the spark plugs to a serious problem with the engine, I don't know, but thank you for your suggestion, I'll tell my dad about it.

 

I would start by cleaning the throttle body then take it from there.