I noticed about 2 months ago that my montero was not getting the MPG its supposto be getting, yesterday my wife altered me that the service engine light came on. Today i took it to a friend who has a scan tool. He hooked it up and this code popped up.

PO173: Fuel Trim Malfunction (Bank 2)

My buddy said most likely vacuum leak. When i got home i checked all the vacuum hoses, i sprayed carb cleaner all around the intake manifold to try and see if i could get an idle difference, no luck.

I do notice when its in idle, it has a slight rough idle, it feels like a miss fire but its not. Whats first to check? MAF sensor? how would i go about checking that out? also i did replace the bank 2 (one before the CatConverter) O2 sensor about 4 years ago, the original one went out. My Montero has 121000 miles on it.

Suggestions please, hope others have come across this engine code.

 

Hi Granny, It sounds to me that you have a valve hanging problem.. How is the timing belt .. I had to change mine at 120,000 just food for thought...

 

Connect the scan tool and check for misfires. Hopefully you can ID the cylinder that is giving you trouble. Can have multiple reasons for a misfire, but that can explain the fuel trim code.
You can also check the O2 functionality while connected.