I own a 2002 2.9 S80. I have a intermittent problem with rough idling. It happens right after I start the car or shortly after. The engine will idle rough but not stall out if I accelerate the engine it smoothes out. This usually last for a minute or two then it will go to normal idle. I noticed that if I turn the car off and restart it goes away also. There are no error codes from the computer although my service engine system required does go on. I thought of changing one or more of the following crank position sensor, cam position sensor, spark plugs, fuel filter but have not done any of these. I prefer not to guess at what is wrong. it does not seem to be a major problem but I am concerned about it getting worse. The car has 128,000 miles on it. If anybody has any ideas about the problem I would appreciate it.
Thank you

 

Clean your MAF sensor and perhaps a cleaning of the ETM is due also.

 

My Volvo is the 2.9 I6 non-turbo I believe the ETM is located between the air filter and intake manifold, closer to the manifold that the air filter. If I am right it is easily accessible. All I would have to do is detach the rubber hose and take the 4 bolts off the attach it to the intake manifold to clean it. It looks like detaching may not be nessary. I saw on line someone cleaning one but it was a turbo version and the ETM it was further down towards the bottom of the engine bay which made it harder to get to. I don't know where the MAF sensor is. I am assuming it is also located between the air filter and the intake manifold. Is this correct?

Thanks

 

let me guess...

it's worse when it's cold out?

I've run into this twice, car runs bad for the first 30-sec to 1 min, then comes to life.

first time is when i changed the plugs replacing the stock 4 point to platnium--bad all
i quickly put the 4 point back in.

second time my indy thought he would be nice and replace the original with "his favorite brand" car runs bad initially. He threw the 4-prong out. I'm just going to live with it.

not sure this is your issue, but it was mine.

 

I bought new plugs but haven't put them in yet. I am scratching my head thinking how can something be so intermittent. The car runs fine 99.9% of the time. As you can see from my previous message I thought of all different kind of sensors and plugs. However I believe if now that #1 I would have an error message and #2 the rough run would happen more often. I now believe that the reply that 537playing wrote probably has some merit. Inside the ETM there is a flap that opens and closes if that flap gets hung up slightly it will give a signal to the computer that is slightly off thus causing the motor to idle roughly. Running the car a little bit longer will loosen the flap to the point where it no longer gives a bad signal or turning the car off and restarting it returns the flap to its original position (since it has been loosened up by starting it once it is now no longer out of sync and will give a proper signal). That’s why turning the car off and restarting it resets the system. If the problem were plugs I don’t think it would reset in such a manner. I am not a mechanic and I am still essentially guessing I am planning to clean the ETM personally this week end and wait and see if the problem occurs again.

 

These two are common maintenance areas as the car gets into some higher mileage. 128k is not all that high, but perhaps some TLC is required. Your description suggests the ETM may be not operating as smoothly as it has. Both devices are critical to air flow management. In my opinion you'll be able to better clean the ETM if you unbolt it from the intake manifold. The MAF is on the air feed tube coming off of the filter housing. It's footprint size is roughly 1 x 2", remove the two screws and wiggle up and off.

 

you might have a leaking injector or leaking fuel pressure regulator. It will flood one or more cylinders with fuel creating a misfire. That is until the extra fuel is expelled thru the exhaust or burnt. Then all is fine.