Voltage to Mass Air Flow sensor on 99 V70XC

warcraftjunkie · Post by **warcraftjunkie** » 10 Aug 2012, 14:05

So I'm troubleshooting a possible Electronic Throttle body issue on my 99 V70XC.

The problems I'm having are basically a rough idle in park for about 5 seconds after it starts and it then settles in at about 900 RPM. When I drive the acceleration is extremely sluggish and many times there is no correlation to the accelerator pedal position and the RPM's of the car. It seems to slip in and out of Limp Mode. Sometimes I get the acceleration I'm used to, but then at about 3000RPM's the bottom falls out and it limps. If I back off the gas and let it coast a bit I can often get it back up to speed, but usually it will limp along as though I had just taken it out of Park and am not pressing the gas pedal... cruising along at 3-4 miles an hour.

I've checked the vacuum tubes, Turbo tubes from the valves on the side on the airbox, etc. All look good. I sprayed starter fluid spray around all fittings while car was running and didn't experience any surging or stumbling.

I've been following the XeMODEex ETM flowchart as my guide. I've pulled the codes at my local autozone and came back with P0102, P0453, P0135. according to the flowchart I need to troubleshoot any MAF codes first as they can often present problems that appear to be Throttle body. First I removed the MAF Sensor and cleaned it with Air Flow Sensor cleaner and let it air dry for about 30 minutes in the warm sun. Put it back in, and the problems are the same.

Next I probed the wiring harness to the MAF... wire 1 and 2 are ground, when I connect to the positive terminal of the battery and pierce the wire jacket, I get 12v on both first and second wire. The third wire is supposed to be the power supply to the MAF with the fourth wire being the signal wire. When I have the ignition on (but engine not running) I measure about 2.10v on the power wire (3rd). Shouldn't this be 12v going into the MAF?

warcraftjunkie · Post by **warcraftjunkie** » 11 Aug 2012, 01:53

Also forgot to mention that as part of my troubleshooting, I changed the fuel filter... well that was over due and not really part of this effort, but it can be removed as a possible problem. I also forgot to mention in my description of the problem I am getting the classic RPM hunting when idling during that initial period after starting the car... revs from 500 to 1200 RPM for about the first 5-8 seconds after car is started then seems to settle in where it should....albeit a rough idle.

warcraftjunkie · Post by **warcraftjunkie** » 14 Aug 2012, 18:13

No input on what the voltage should be to the MAF?

In the meantime, I pulled the Throttlebody and it was a little dirty, but honestly I didn't think it was that bad. I'm most likely looking at a replacement if the culprit isn't the MAF. It's been replaced before by previous owner cause the label is yellow. If I replace it, it will be a XemodeX rebuild. Don't want to have to do it again.

Post by **JimBee** » 14 Aug 2012, 20:32

The voltage numbers I've seen for the MAF are right around 1.0 on pin 4 at idle; smoothly up to around 4.5 at 3500 rpm. 5.0 v. is supposed to be the max output and that's on pin 4.
Check out this tech writeup:
http://easyautodiagnostics.com/Volvo-MA ... est-c.html

Using a digital multi-meter, you should see stable numbers at whatever rpm level. If the numbers are too low or too high and especially if they're unstable (which would really show up on an oscilloscope but are pretty obvious on digital meter, too) then the MAF is bad.
UNLESS you aren't getting steady 12 v. in on pin 3 (I think). I believe pins 1 and 2 are grounds. One is an internal ECU ground, the other is an external ground. If those are faulty, you probably can't know if the MAF is capable of putting out the right voltage.

I use a 1 1/4" brad with a head on it. Just slide it along the wire into the plug until you hit metal. That will give you a good contact and correct reading.

warcraftjunkie · Post by **warcraftjunkie** » 15 Aug 2012, 01:59

On Pin three using the method you describe above I'm getting about 2 volts. so there's some electrical loss somewhere? When I connect the + terminal of the battery to that brad I'm measuring a solid 12volts.. actually it's a little higher than that. I need to come up with a rig that connects the MAF to the battery for a road test to see if it improves the performance.

After cleaning the Throttle body and reassembling it all together it seems to run a touch better, but it's honestly probably just wishful thinking. Still hunting for RPM's at idle. Loss of power. Its as if the Turbo is completely taken out of the picture... I don't feel that punch kick in at about 3000 RPM. Is it possible that a failed Turbo could be culprit... or would that basically disable the vehicle?

I think it's time to take it to my local independant Volvo shop for a better mind than mine.

Post by **JimBee** » 15 Aug 2012, 05:53

The voltages and grounds I know about were quoted for a '98, I'm assuming they're the same for others using similar system. Try to confirm that.
Hopefully, your Volvo mechanic will be able to solve it. In my experience, they don't measure pin voltages or even know what they should be, just go by codes. If the code says it's a bad MAF they replace the MAF and that's supposed to fix it. The thing is if you have a bad/flaky ground in your computer box, that could mess with the voltage. If you're getting 2 volts max out of your MAF, the engine is starving for fuel b/c the computer thinks much less air is coming in than really is. From what you describe, it looks like the issue might be the 12 volts to the MAF is a partly open circuit or poorly grounded.
I guess I would start there with the Volvo mechanic. If he doesn't get that, you don't want him throwing away time and money on "well let's try this part" forays. If he has a known good MAF lying around and wants to try it without charging you for it, great. Or if he'll let you try your MAF in another car he has there, you could check it that way.
You can pull the computer box and check wires to the MAF from there. If he knows how to do that, you can probably get to your solution faster. If you have multiple probes in the MAF wires, be careful not to short anything back to the computer.
Good luck.

warcraftjunkie · Post by **warcraftjunkie** » 15 Aug 2012, 13:22

Ok, took it out for a spin this morning and have a few more details to add. Perhaps I'll just cloud the troubleshooting, or give that missing piece of info.

I got it up to the interstate speeds, it was sluggish getting there, and the turbo definitely didn't kick in. When I got off the freeway and was approaching a light, it started stumbling again with the RPMs. The brakes suddenly got soft as I came to a stop and the Arrow light that indicates that it's in Winter mode came on for about 2 seconds. No matter what I did, it wouldn't acclerate more than just rolling speed. I was able to limp it off the road into a gas station. When I hit the transition from the road to their entrance that bump seemed to do something because my power was suddenly restored. Not all of it mind you, but it was back to what it was just before it bottomed out.

Puzzling....

warcraftjunkie · Post by **warcraftjunkie** » 21 Aug 2012, 18:15

Well, they said it's the Throttle Body. Looks like it's time to order my rebuilt one. I'll post with my results once it's in.

warcraftjunkie · Post by **warcraftjunkie** » 21 Sep 2012, 20:53

So, I installed the rebuilt throttle body from Xemodex, and I'm sad to say, the problems are the same. In fact I got a new error code of P0121 (Throttle position sensor). I swear this is starting to feel more and more like an electrical issue. When I go over a bump sometimes the power returns and I'm able to drive great, and then I hit another bump and its as though the rug has been pulled out from underneath me.

Post by **Pauloil** » 22 Sep 2012, 05:35

did you unplug MAF to see if runs better unplugged? did you reset adaptives?