Volvo Repair: Volvo S70 1999 ETS light intermittently comes on, mass air flow sensor, mass air flow

Question
I bought my Volvo S70 1999 back in January of this year.  I just
this past week started having problems where the ETS light
would come on almost exactly in the same place of my commute
(it's done this twice now).  I get a rough ride as soon as I start
slowing down. I pulled the car over and turned it off, then I
turned it back on.  The ETS light goes off and then it runs fine
again.  Also, if I put the car in neutral while slowing down (and
the ETS light is on) it doesn't idle so rough.  Is there something I
can do to fix this myself, or do I really need to take it to a
mechanic?  If so, what kind of $ am I looking at?

Thanks,

Robert

Answer
Hello Robert,
Firstly, sorry this late response, but I was not in office, so I could not reply, sorry...
Your problem is regarding with Electronic Throttle System (ETS). It is a part of emission system that is a combined system of inlet and exhaust side. At inlet side, the parts are mass air flow sensor, Electronic Throttle Module at exhaust side the parts are oxygen sensors (fron t and rear)
All of them work together, they effect eachother. So if one of them is defective the car should not be driven more, the others can be effected.
For your case, the ETM started to break down, so do not drive the car with this problem more. Firstly solve the problem. As first, the ETM clean can be tried, it takes approx 2 hours so you will pay only 2 hours labour. If it can not be saved with cleaning replacement of it will be necessary, it is expensive approx 800 USD as I can remember.
Also, when you go to the dealer, ask from them there is a Software Upgrade for ETM, Part no is 30677007, it will be beneficial for this car.

Regards...