My 01 volvo s40 runs fine with the air on as long as im driving. When i come to a stop like at a light within a couple seconds the battery light comes on, the radio cuts off like the cars going to die (which it has before and i had to get it jumped) If i turn off the a/c real fast it goes back to being fine...any suggestions on what this could be?

better just to replace them you could damage the others taking them out

ok everyone not trying to be unappreciative of your input and ideas however only w couple of you are even looking in the right area. generaly when your check engine light comes on its telling you your car is misfiring (obviously). its basically a caution light not so much a stop pull over and run type of light. yes you can damage your cat over a prolonged amount of time with no repair. so my thoughts on this are that is has to be the ignition coils. I drive a 90 vw and a 96 monte carlo. i just recently had this issue with my monte and first thing i did was replace the coil packs (ignition coils). result...light went out and not flashing or anything and perfermance is restored, all is well and it runs great. give that a shot, im 98% sure that will take care of your problem, and in your s40 there should be 2 coil packs, typically only one is bad but im that type of guy who doesnt wanna worry about the other one at all so i just replaced them all. they're typically around $50 each. my monte was $36 for 1 and there are 3. your s40 will only have 2 and there located directly under the plastic cover on top of the motor. hope this helps, good luck and dont waste your time searching in the wrong placed, check engine lights are usually sensors of an ignition misfire so if your not sure which one then just limp the car down to autozone and have them plug it in for free.

MOST TIME IF YOU GOT MISFIRE ON ALL CYLINDERS.YOU COULD HAVE AIR LEAK IN INTAKE MANIFOLD.OR PROBLEMS WITH EGR VALVE.ALSO YOU COULD HAVE A DIRTY OR STICKING FUEL INJECTOR AND A BAD COIL OR SPARK PLUG.

I think it may be the battery or the alternator not the maf sensor.Sounds like its not charging thats why it runs rough when you are running multiple things at the same time.Have your battery and alternator checked first.Hope this helps

the maf is located on a black plastic pipe 50mmdia beside the air filter (the air filter is located in a black plastic box 300mmx150mm approx)the maf is held in with two screws

could also be a "CEM software upgrade" but I recently found a pinched wiring harness in a passengers side door creating an instrument panel going out in an 01 s40. go figure. If its a software upgrade, it would run about $60-100 depending on the dealer.

turn the key on to position 1 preset miliage trip button anh hold for 2 second release and turn key to position 2 hold within 4 secods and hold til manitance info clears.

mine did this.lift the back seat and remove the fuel sender out the tank.youll see its full of gunk..

you probably have air on the lines or the brake booster is bad.
try purging out the lines first and see if that helps

your IAC valve, idle air control valve is under the black plastic cover on the front right corner on the engine, remove cover undo valve, renew gasket and re install. ade 13 years volvo tech