1998 v70r vacuum leak

[tardcart]

also, the bugaboo on the 95 and earlier 850's is the EGR valve. but I cant help with that since I avoid so equipped 850's

[erikv11]

you cant loose enough vacuum on the line to the PTC to upset the MAF. It may cause some idle roughness but no code. ...

This is inaccurate - a break in that line from the nipple to the PTC throws p0172 on these cars with very high frequency.

Cleaning the MAF is usually a waste of the few bucks you spend on MAF cleaner, unless the MAF is visibly oily or dirty. At the least test the MAF first: with the car off unplug the MAF, then drive it around for a while. If the MAF is broken (or dirty) then the car will run fine with it unplugged. This test will of course throw a MAF code that will need to be cleared.

p0172 is almost never a MAF problem - first line of investigation is to look for vacuum leaks.

The factory line from the IM nipple to the PTC is hard plastic and also known to get brittle when aged and break somewhere in the middle, buried under the IM. I would try running a replacement bypass line see if that fixes it (e.g. the post by matthew1 here viewtopic.php?t=47383), that's a cheap and easy test. You can just leave that line in place, too, or route it under the manifold etc.

[erikv11]

also, the bugaboo on the 95 and earlier 850's is the EGR valve. but I cant help with that since I avoid so equipped 850's

I hear ya! I got rid of the EGR on my 95.

[tardcart]

Erikv11, Did you change to a 96-97 ECU so the absence of the EGR wouldn't cause a check engine light? Or did you put a resister on the line?

[erikv11]

I changed the ECU, that's also how my 95 is running Motronic 4.4. Changed the intake manifold to get rid of all EGR plumbing. Only the EGR solenoid connector in the wiring harness remains.

[dcmike]

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I unplugged the MAF and the car ran worse. The car threw 2 codes P0172 and P0102, a miss fire. Plugged it back in and no more miss fire

I removed the hose from the IM to the PTC when the car was running and the idle calmed down. So I am assuming the hose is good. The crankcase breather system was replaced 2 years ago and the hoses are still soft and pliable.

All of this started after I replaced the master cylinder. I sprayed brake clean in the area below the master cylinder to remove excess brake fluid. The connectors for the O2 sensors are there. Could the O2 sensors connectors been damaged to create this problem?

[RickHaleParker]

P0102 is MAF. Misfire is P0300 - P0305.

[dcmike]

Still nothing, but new codes. P0175, 0131, and 0141. This is getting very frustrating. Any other ideas or advise.

[tardcart]

just a thought, the booster uses a lot of vacuum, if the line were off or rotted out or the booster leaking that would account for your problem. My booster line was hard and broke when I removed the intake manifold. also check the one way valve so you arnt turboing the booster. ( no bearing on this problem) also dont spray break cleaner around it it destroyes rubber and paint but probably not related to problem. also break fluid eats up paint and rubber. but the chances are good you moved something to cause this while working on the master cylinder.

[dcmike]

My last hope before taking the car to the volvo repair shop worked. I added a can of 44k fuel system cleaner and for the last hour of driving no problems.

The car sat for a month while I did a bunch of work to it and must have went bad.

Could an injector been stuck? I was getting about 35 psi at the fuel rail.

I’m still getting the p0131 and p0141 codes but no more 0172. I have had the other codes for awhile.