I have recently purchaed a 99 V70 FWD 94k miles. Runs great but 2 weeks ago the Check Engine came on indicating a bad front O2 sensor. Before it was replaced the car started to stall during startup. Outside Temp was in the mid 30's and rainy. Did it a few times from a cold start and also after driving 3-5 miles to go to the store. Car would sit 5 min with engine off and stall upon startup. It catches after several times and runs great after that. Replaced front O2 sensor and car continued to stall even as the outside air temp went to 50 and dry condtions. Check Engine light now comes on 5 min after codes are zeroized. Code now reads rear O2 sensor and Manufacture Fuel Contol Metering in that order. The car does not idle surge when stopped or while driving. My Mech says it is running rich and will need a new Throtle Body for about $1000. I am in the process of checking the fuel milage to see if it is out of whack. Does it just need to be cleaned or replaced?

Help!!

A dirty throttle body is possible, a new one is unheard of. I believe the 1999 had throttle by wire, and if so, may need a new ETM. Lets hope not, they are expensive.
Start by cleaning the TB and inspecting the elbows on the vacuum lines, especially the one that goes from the front of the engine and around the passenger side to the back.

Klaus
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(1975 164, 1995 854T, 1998 V70R)

Thanks for the quick response! My Mech told me this is an electric TB. Would a dirty TB cause the rear O2 sensor to kick off the check engine light? Would a dirty TB cause it to run rich?

After riding it last night I did notice the smell of fuel which makes me think it is running rich. I seem to think the cause of the light is due to this rather than the O2 sensor. I'd rather not spend another $219 for another O2 sensor if that's not the problem.

Have you ever used SeaFoam to clean the system?

I am about to clean the TB on my 1 year older V70. What I use is gasoline and a lint free cloth. I know, no smoking while work is in progress. I also clean the electrical contacts with cleaner and coat with di-electric grease. My turbo air tubes are coated with oil deposits, so they will have to be cleaned along with the vacuum lines that go into the turbo piping.
Carb cleaners are a no-no because of the plastic/rubber bits in the TB.
As far as the ETM is concerned, I was told that only dealers can replace them because of the new software download requirements. Latest I heard was $800, but your dealer may charge more. Always ask for a discount! And keep your service receipts.

Klaus
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(1975 164, 1995 854T, 1998 V70R)

Thanks Klaus, I'll give it a go. Also, I have have been smelling a slight Sulfer (rotten egg) smell right when I get out of the car. Does this add any info to the problem? Why would it smell like sulfer?