I'm new to the site had to make An account just to post because I couldn't find anything that helped me. So I bought a car had problems with a pnp switch dealer said they would replace it took it to their mechanic while he was fixing that he broke my maf but said he replaced it when I went to take it back from the mechanic it had the cel on I asked him he said it would go away when the new one cycled well it never went away I took it back and forth a couple times. The first time he said it was a faulty maf so he warranties it out and replaced it. The next time he said he spent hrs diagnosing it but now we are to where he now says he has no idea and to take it somewhere else. Ok so he said he checked the maf vacuum lines with a smoke test also said he smoke tested the exhaust and said he check the use pressure and t was at around 35 so it was in spec. Told me it could need a fuel trim reset. I'm getting a running lean code (p0171) and very rarely will get a misfire but that's happened like twice. I replaced the fuel filter and fuel pressure regulator. I tried to spray some vacuum lines on my own with no success. I checked the plugs they don't really look like they've been running lean. on the occasion it's hard to start when cold and will die when it comes to a stop not often though. Sometimes it will bog down on acceleration but again not often at all. Any ideas? Could it be a fuel pump going bad or possibly the o2 sensor was bad? I thought that the o2 was actually doing its job here though. Exhaust doesn't smell or anything like that. I don't hear a ping from detonation. Running normal temp so it doesn't seem to me that it's lean at all but I'm also new to volvos. All help is appreciated. Thank you. UPDATE. I also received a misfire on all cylinders this morning from a cold startup it was better after about 10 seconds and ran fine afterwards. Another update hopefully somebody can help. I have replaced the maf 02 sensor fuel pressure reg map sensor cleaned the iacv and throttle body. With my obd2 scanner I have found out it's getting the right amount of air through the maf right pressure in the map air Intake temp reads correct. The 02 bounces between .1 and .8. I'm running out of ideas. Also if I put it in reverse or drive the rough idle goes away right away.
Any help would be nice thank you.

 

A faulty Inlet Air Temp' Sensor (IAT) can affect the fuel mixture especially at cold starting.

 

Bump any help please?

 

coolant temp sensor can do the same. Nothing here is specific to Volvo... VW, Audi, BMW etc all use similar air metering designs.. Have you checked fuel pressure (possible fuel pressure sensor/regulator issue?) Also did you check for positive crankcase pressure ie a clogged PCV system? Also, did you use an OEM or aftermarket replacement MAF?

 

i replaced the fuel pressure reg already. And I did check the pcv it was good. Also I replaced it with an oem maf.