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My 1995 850 turbo sedan started giving me grief today.
First indication of any trouble is that it stalled (just stopped running) at the traffic light. Started right up again and seemed ok.
Driving, it is intermittent between perfectly normal, and stumbling/rough running. If at idle, it may die. Other times it runs just fine. Check engine light eventually turned on during a long period of stumbling.
Tachometer does not drop when it stumbles - I'm taking this as indication that ignition (at least on low voltage side) is ok.
When it's stumbling, I can rev it up and accelerate, and it will typically accelerate through it. Thus, probably not a fuel blockage or partial blockage.
Since the tank was very low, (maybe 3 gallons left,) I pulled into a gas station and added 3 gallons. No change.
When I got to work, I did a quick cursory check that all air hoses are in place - did not notice any anomalies, though I was in a dark parking garage and trying to stay clean.
Pulled A2 codes, and got 414 (Boost Pressure Regulator) and 121 (MAF Sensor Signal Absent).
Searching in the archives, others experiences seem to suggest a failed/failing MAF. Not clear if disconnecting MAF will result in a drivable car, or just a car that will idle ok for test purposes.
Any other thoughts or suggestions? Thanks in advance!
Roger
'95 854T 232k miles
'87 245 M47 275k miles
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Update: I replaced the MAF sensor, and it seems to have taken care of it. It still idles a little rough - it was running horribly rich, and I think I need to clean all the spark plugs. I was able to do a few WOT bursts which helped, but it's not yet "all better". At this point, I have ~35 miles on it, with no stalls and no more codes, so it's looking good so far.
Interesting note: When I did the "unplug the MAF" test, it would start, run like a top for exactly 10 seconds, then stumble for 2 seconds and die. It did this repeatedly (4-5 times before I moved on.) I don't know if 10 seconds is the end of the MAF Substitute Signal, or if my plugs were so fouled that when something changed from "start" mode to "run" mode after 10 seconds, it just couldn't sustain running.
Thanks everyone for the help!
Roger
'95 854T 233k miles
'87 245 M47 285k miles
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Check the vacuum lines going to the turbo. There are 3 of them and will turn brittle with age & heat. If you pull them off or replace them, do it one at a time. It can be confusing and crossing them with each other will lead to all sorts of problems.
To verify the MAF as a problem, turn the engine off, disconnect the MAF plug, and start the engine. It should idle fine but run terrible at speed. Do NOT plug in the MAF while the ignition is on, or unplug it for that matter.
Some have used MAF cleaner will limited success. If you replace the MAF, get OEM only.
Klaus
--
Why are Volvos so endearing? Its just a car.
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Thanks for the suggestions. The vacuum lines are in pretty good shape - replaced not too long agon when I had other things apart. I did double check them, and all seemed in order.
I could not definitively conclude MAF last night - in the garage, it performed flawlessly. (The joys of an intermittent issue.) Before departing work yesterday I performed the "clean the contactors by disconnecting and reconnecting 20 times. It ran fine for ~20 minutes (half way home), then started stumbling again. Testing in the garage later, all worked fine. Unplugging the MAF gave the expected result as the ECU used the substitute signal.
Do you know what the MAF failure mode tends to be? I imagine that open circuit or short circuit would be an outright failure that would cause the substitute signal to be used; is there a typical "erroneous signal" failure mode?
Roger
95 854T 232k miles
'87 245 M47 285k miles
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Here's more info then you want, i'm sure...
Code 1-2-1
If the signal from the MAF sensor is lower than 0.2 V or greater than 2.2 V at idling speed, or is considered unsatisfactory according to RPM and throttle angle, this is interpreted by the control module as a fault and DTC 1–2–1 is set.
Substitute value
-The control module uses engine speed and throttle angle to determine the load.
-The IAC valve's idle air trim is inhibited.
-Long term fuel trim inhibited.
-Only initial charge pressure is permitted.
-The EVAP diagnosis is inhibited.
Possible source
Signal too high:
-Signal lead short circuited to voltage supply.
-Break in lead to signal or power ground.
-Defective MAF sensor.
-Contact resistance in connections.
Signal too low:
-Break in signal or voltage lead.
-Signal lead short circuited to ground.
-Damaged or loose fresh–air hose, upper charge air cooler pipe or lower charge air cooler pipe.
-Defective MAF sensor.
-Contact resistance in connections.
Fault symptom[s]
-Uneven idling and/or jerky operation.
-Poorer performance from initial charge pressure limit.
Code 4-1-4
The ECM calculates charge pressure by using the signal from the MAF sensor. When the ECM considers that the MAF sensor is correct and the load signal exceeds a preset level, DTC 4–1–4 is set.
Substitute value
The system only permits initial charge pressure.
Possible source
-Defective MAF sensor.
-Contact resistance in connectors.
-Break in the lead to the charge pressure reduction from AW 50–42.
-Clogged hoses between turbocharger (TC) and TC control valve, and TC control valve and pressure servo respectively.
-Defective TC control valve.
-Defective pressure servo to the wastegate valve.
-Seized wastegate valve.
Fault symptom[s]
-When charge pressure reaches the max. limit, fuel injection is stopped. As a result, the engine becomes very jerky.
-Poorer performance from initial charge pressure limit.
If I'm reading this right, it seems that your computer believes the MAF is right and the load is wrong. So most likely would be a bad MAF, though other things can cause it. It would be more labor on your part to check everything else but easier on your pocket book not to start with the MAF...
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As one who's had to go through this, (and hopefully done with it, but with intermittent things who knows?), MAF's most likely. Check your plugs and see how dark they are, because mine would turn black...
Do you know the last time your PCV system (flame trap) was cleaned? If its been some time you might want to look at it because the dirty system could kill your O2 sensor. A bad O2 sensor could do this too, but with your MAF code its most likely the MAF...
I don't think that taking it out (limp mode) would run much better than it is now, but maybe you could check it. A MAF cleaner might clean it and solve your problem, but you might have to get yourself a new one. Check Pick-n-Pulls near you cause sometimes they have them still on the 850s. Also, if they don't work you can trade back for store credit.
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