Just yesterday morning my wifes 1999 V70 XC started running rough and the Check Engine Light came on. Due to the loss of power and the shake, it seems like its not firing on all 5 cylinders. I also can smell a faint gasoline smell, which could explain a cylinder not using the gas. I took it in to AutoZone to get the CEL code, and the code was: P1171. Doing a google search it says its either a bad MAF (mass air flow) sensor or a dirty throttle body. The autozone guy also said that there was a cylinder 1 misfire, which leads me to my original theory.

Tonight I plan on doing some troubleshooting by replacing the spark plug, disconnecting wires one at a time to narrow down the cylinder, and perhaps swapping coil packs to determine if the coil pack is faulty. Based on your experience would you think that it could just be a bad MAF instead of a firing problem? About 4 months ago I did clean the MAF with typical maf cleaner so being dirty is not an issue. Also, is the car safe to drive while I determine the problem and get it resolved?

Thanks in advance for any help you are willing to give.
Ryan

 

The fuel trim code could be a vacuum leak in either the intake system or exhaust system. But it isn't likely to cause the misfire. That is much more likely to be plugs or a coil. Check to see if the coil is firing and if not, switch it with one that is to isolate the problem to the coil. If its not firing, replace it and I would suggest new plugs at the same time. Then clear the codes and drive it and see if the other returns.

I would drive it minimally in the meantime so you don't damage the cat.

 

Unclip the MAF, see if she runs? then clip it back on and see if its different..

That would either diagnose or eliminate MAF for ya.

 

Thank you everyone for your responses. I was able to fix the shaking / loss of power issue by replacing the ignition coil in cylinder 1. I do have another CEL code even after resetting them. P0014, which references a camshaft position sensor. This code was on at the time of my original ignition coil issue, but I thought it may be related and go away once I fixed the issue. The car runs completely normal, so I am curious on why this code came on at the exact same time as the one for the ignition coil. Do you think this has anything to do with my original issue with the ignition coil, or is this just a coincidence it came on with the other one? Let me know if you have any ideas. I appreciate the help so far.