Feels like missfire, but very slightly
 

Last couple of says i have noticed while standing at a red light the idle would go down once or twice and then get back to normal, the car would vibrate slightly at the same time. maybe the lights slightly dim for that split second too

2 coils were replaced by previous owner, two by me this summer, 2 original, and all new plugs this summer

today on the way home from work, it did that twice again and then the check engine light came on, last time i had a missfire the power went down really bad, acceleration was very soft, and if i accelerated hard the check engine light would flash (codes said two coils were bad, replaced both and had no codes and no problems), now it feels a lot less affected by whatever is causing it, check engine does not flash just stays on solid, going to mech tomorrow to scan the code, have a good feeling its the coils again - at least i hope so cause its an easy fix ... if not what else could it be ?

question: does check engine light always flash for a missfire (for me it did only under hard acceleration)? or if its a mild missife only by once coil pack then it doesnt flash ?????

I've had rpm drops at idle before on my 2000 S80. Turns out it was a very dirty throttle control valve, (the butter fly valve where the plastic intake hooks on to the intake mainfold.) Was very easy to remove and cleaned it with carb and choke cleaner. The PCV vent is right before the valve. If the pcv system is clogged, or if you have a little blow by getting through it really gums up the valve. Kind of causes the engine to "choke" and not get enough air. Then the electronics kick in and send the rpms back up again. I even had a few scary moments when the rpms jumped and it caused the car to lurch forward!

i have the same symptoms exactly that you have (even though my car is finally fixed now lol) and i can tell you that if your engine is misfiring, the light will flash no matter what. i think this is one of those imfamous ETM failure symptoms.

no its not an etm issue, i wish people just stopped throwing out etm at every problem out there,,

look at my other thread, i made it after i made this one, (after i scanned the car and realized what it was)

anywaysi did have miss fires before when 2 coil packs went bad and that was not fun, but an easy fix nonetheless

kevmcrae; got any instructions on how to remove the TB and clean it ? do i need to buy a new gasket from volvo ?

i did this on another car and it was easy, just had to replace the gasket

Hi andrei3333,
Sorry I haven't been on in a while. Throttle body was very easy for backyard mechanic. Even without any instructions it is pretty simple. There are two gaskets. Best to buy and replace both.
Kevin

Sorry Andei3333. There are NOT two gaskets. For some reason I was thinking you were asking about taking off the intake manifold. For that there are two gaskets.

For the throttle body there is only one gasket. It is reusable if you're careful with it.

To remove the TB, remove the air filter box, then all the plastic intake tubing leading to the engine intake. The TB is the first metal piece where the plastic tubing ends just under the intake manifold itself. Disconnect the wiring harness from the TB. Be careful to remove it correctly so you don't damage the clip. There are 4 bolts holding the TB unit on to the manifold that you access from the bottom of the unit. A 1/4 inch ratchet works great. After removing the bolts the unit comes right off. Use carb & choke cleaner to remove the carbon build up around the butterfly. Be sure to clean the butterfly hinge points really well. You don't want any little particles of carbon to interfere with the operation of the valve. Re-assemble in reverse. The torque setting on the four bolts is VERY light, 18lbs I think. It doesn't take much to hold it.

niice, thanks for the instructions, pretty cold to do that right now, so i will copy paste this and save it for later,

sounds just like other car i used to own, if its a metal crush gasket it can be reused, but if its not too expensive is rather replace it....