Code P0172 (not a vacuum leak)
 

Hello everyone. Perhaps someone can help me. This is about my 1995 Volvo 850 Turbo Wagon with 120K miles on it. A while ago I got the P0172 check engine light. I looked it up and found that the most common cause was a bad vacuum elbow. That is what it was. I fixed it and problem solved. Well about a year went by and last week the same code came up. It also has lost any upper end power. At around 2800 RPM the car just stops giving me any real power. The tach just sort of stops and the car feels like all the power is being robbed. Well I brought my car into my mechanic and he pressurized the system with a smoke machine and found the fresh air hose was leaking. I replaced it, cleared the code but still had the no power issue. Two days go by and the light comes back on. I bring it back to my mechanic who re-smokes the car and finds out that the hose I replaced I miss aligned a tab and didn't seat it on the turbo good. He has been great about bringing me into the shop to see what is going on. Anyway, they reattached the hose and replaced one other small vacuum hose. No more leaks now. But the car is running really rich. Hench the code. OBD2 is a little vague but the OBD1 pulls a code for the front 02 sensor. Fuel pressure was good at the rail too. So, yesterday I bought the sensor and all my tune up stuff from Volvo (ouch that was expensive). Yesterday I did plugs, cap, rotor, air filter (the old plugs looked fine. Just a little light gray) and srayed the MAF really good with MAF cleaner. Today I did the front O2. I cleared the code and disconnected the battery for 1/2 an hour. Well, the car is still getting crap for gas mileage and still it hangs up around 2800 RPM and I have no power. Other than the bad mileage and no upper end power the car idles great, drives fine etc. No backfires, no skips or misses, no smoke out the dipstick (unless I rev it with the stick removed). Also, the car has a new fuel pump and filter. There was also some oil (tablespoons amount) under the spark plug cover.

What the heck do I look for now? My wife wants me to bring it to a Volvo dealer and I would rather find someone here who has had this problem or knows what it might be or can ask the proper questions of me to help me figure this out.

Any and all help is greatly appreciated. Thank you for reading.

Kyle

Also with this problem. Once in a while upon start up it runs like crap and I turn it off wait a minute and restart and it starts and idles and sounds fine. Another forum is saying it might be the fuel pressure regulator but I don't know if this makes sense to me. I guess it would if when the pressure regulator was given more vacuum it increased the fuel at a greater ratio than the 1:1 it is supposed to based on vacuum.

Thoughts? Also, I have been reading so many old posts and haven't found the same exact problem. Thanks for the help,

The Maf might be going bad.

Thanks,

They thought so too. We all did. But it kept testing OK. My shop had the car all day today and went through everything. Long story short...they found the problem. The connector at the computer was slightly corroded and was causing a voltage drop from the components (mainly the rear O2). This was causing the computer to compensate and make it run rich. They cleaned the connector really good and it is like driving a new car again. The shop owner took this on as a personal challenge today and spent over 8 hours with it. Had the head mechanic at Farrel Volvo drive it with him with the 850 specific computer reader too. He is only charging me for 1 hour of labor too!!! He was too funny when he called to tell me it was fixed. He said it was like driving a car with a Turbo (which of course it has but felt like it didn't).

So, I now have new vacuum hoses, new front O2, new FPR, full tune up and now a cleaned computer cable. But it runs awesome.

On my drive home from my mechanic (7 miles with stops) I drove it with a real heavy foot and I got 23 MPG. Much better than the 13 when it was acting up.

Thanks for the help.

Glad all is good now.