Mass Airflow Sensor?
 

Here's another question for you wise ones of all things Volvo:

My 1993, manual 240 wagon usually runs beautifully, but recently it would run rough, die when idling, stall out when I tried to accelerate, and the upshift arrow dash light would flash. In the beginning, this would only happen after it had been out in the rain for a while, once every few weeks. I then replaced the distributor cap, rotor, plugs and wires, but the problem did not go away. It only happened once in a while, and I learned (from this forum) that disconnecting the negative battery cable can reset things, so I started doing that, and the problem would go away for a while (a week to a month).

Today I had the problem again (without the upshift light flashing), and -- for the first time -- it happened in dry weather and -- also for the first time -- disconnecting the battery did not help. So I remembered something else I read on this forum about a mass airflow sensor causing this type of problem, so I completely removed the mass airflow sensor (physically and electrically), and the car ran fine (however the upshift light was flashing). I drove to an auto parts store, bought some mass airflow sensor cleaner, and cleaned the sensor and put it back in. I also took out the air filter (which was quite dirty) and tried to buy a new one, but they didn't have one, so I knocked a lot of junk out of it, and it looks a lot better.

I put it all back together, and it runs great now with no dash lights.

So here's my question: should I trust that the problem is fixed, or is there something else I should do or check?

Thanks for sharing your wisdom,

My guess is no, it isn't sorted out. When you say your dash lights are out are you referring to the idiot lights or the backlight used to see the instruments when the lights are on?

If the idiot lights are out, I think you have a bad connection somewhere. All of your symptoms seem to indicate either low battery or intermittent bad electrical connection. All 240s up until '93 had a 25 amp blade fuse mounted on the inside of the front drivers side fender that was always a common culprit for bad connections. Moisture would get in causing corrosion. Since yours is a '93, I doubt you have this. Check the positive connection from the battery and verify all the main connections and fuses looking for corrosion. Check the negative connection at the battery and where it connects to car and/or engine. Make sure all are clean.

Also check your battery voltage. Low voltage can cause all kinds of weird symptoms.

Also note that if you drive around with the idiot lights not working on the dash, your battery will not charge.

I've done hours of research into exactly how the MAF works so a test for this is warranted.

1. Back probe the connector on the MAF from pin 1 and ground, you should have 0 Ohms

turn the ignition ON with the engine OFF

2. Back probe pin 5 and Ground, you should have 12 volts
3. back probe pin 5 and 1, you should also have 12 volts
- if you don’t get this the MAF is bad

4. Back probe pin 3 and ground should yield 2.3 volts
- if you don’t get this the MAF is bad


Unplug the MAF

Ohms between pin 2 and 3 should read 2.5-4 ohms
- if you don’t get this the MAF is bad



MAF plugged back in

Probe pins 6 and 7 on the ECU should read the same 2.5-4 Ohms
- If you don’t get this at the ECU but you do at the MAF, fix the connection

Probe pins 5 and ground from the ECU should yield 0 Ohms
- if not fix the connection


because this does not explain the UP arrow as well,
My guess if you are having some corrosion issues in the ECU connector, or damaged wiring
mainly because this typically happens when wet

thanks
 

To Nichals:
Thanks, this is very valuable information. I will try this test of the mass airflow sensor. I'm not familiar with the ECU. I will research this.

To act1292:
My "idiot" lights are working, but the "up arrow" light that normally turns on only when the car is telling you to upshift will sometimes flash constantly when the car is running rough or when I have the mass airflow sensor disconnected.

change or test your your crank position sensor. It sounds a bit like this is getting improper input and telling the ECU that the engine is spinning much faster or slower than it is, this could trigger the flashing arrow.

CPS issues are typically manifested as stalling and unable to restart when the engine is hot. If it was sending signals that the engine was spinning faster you would have all kinds of ignition issues since the engine timing is driven off of the CPS.

Since you have an upshift indicator, I assume that you have a manual transmission, correct? Take a look at this thread on turbobricks. It sounds like a similar issue:

240 Flashing dash (shift indicator) - why? [Archive] - Turbobricks Forums

Thanks for this. BIG help. I wanna sticky this.

Wait, you drove without a MAF at all? That's almost impossible. I had to do it once, I did it by choking the intake with a tool pouch tied over it and I couldn't go over 15-20.