98 v70 with occasional loss of power and bucking

[Volvo_240_Atari_2600]

Weeks later, NEW Crank Position Sensor (OEM Siemens) and we still have the same problem.

Wife won't drive the car anymore. I don't blame her with the kids and all.

I ended up taking it to our local VOLVO independent shop (not a dealer).
Afraid this was going to lead into big $$$$ they found nothing after keeping the car for a day and a half. It never acted up on them. All then did was a throttle body cleaning and inspection and test drives.

So I get the car back on Tuesday night. Car ran fine.
Drove home... Nothing. Yesterday, Drove to work, nothing. Then I had to pick up my son at school at 2PM and it started happening again. Car stalled three times, ran rough, had to rev the engine up.

I forgot to mention Saturday. I had to drive this automatic like a manual all the way home in stop and go traffic (city streets) of about 15 miles.
Car wanted to die every time I came to a red light. Slip the car in neutral and applied pressure to keep the idle up. My wife would definitely not drive the car like that.

Shop did not think it was the MAF.... I am more inclined in that direction now more than ever.

When I quoted them what my wife said "the car some times surges at a traffic light"

What does that mean? She said that with her foot on the brake at a light sometimes the car would intermittently rev... She would se the tachometer jump.

Well this never occurred while I drove it but the mechanic said it could be the idle control valve.

HELP!!! I am tired of dropping money in this car at a moment that it is scarce and nothing I replace or tackle seems to be the problem. This car has been good to us for the two years of ownership until now.

Today I will try driving it w/o the MAF plugged again to see.

By the way… the gas mileage on this car has NEVER been more than 18-19 mpg city-highway… Sometimes on a long distance (highway) drive we were able to get maybe 21
MAF sensor? Even though this problem started now? If it is the MAF sensor causing the stalling and rough idle. Just a thought.

Thanks
Eric

[jblackburn]

It's pretty much a rule of thumb that any time you take a car to the mechanic it'll act like a little angel and your problems won't show up for them. My Honda would do the same bucking thing occasionally, and then worked fine all 3 times I took it to the mechanic. Finally, after much insisting that they keep it for a day and drive it around, it acted up for them, and it turned out to be a loose valve in the carburetor.

Looking back, though, your problem does sound like a MAF sensor. Since you already had a code for it, and describe the twitching RPM and random loss of power, I think it's entirely possible that the sensor's just flukey. Sometimes cleaning it will work, sometimes it won't. Both cars I've had that actually had MAF sensors outright died on me.

The idle control valve could probably use a cleaning and may help your idle a bit, but it wouldn't cause your car to buck or lose power under acceleration.

I'm not saying I'm 100% sure on this, but the symptoms certainly do seem to point in that direction. See how it behaves running with the sensor unplugged and maybe it will give you a better idea.

The bad gas mileage really depends on what kind of driving you do more than anything. 18-19 is normal for city, I get ~20 mpg doing mixed 45-60 driving and stop and go driving. Out on the highway for long periods of time, though, you should be getting more than 21.

[Volvo_240_Atari_2600]

jablackburn

Thanks again for the input.
Back to the MAF... I have cleaned it on several occasions (3) exactly and I am not going to bother anymore.

I unplugged the MAF yesterday afternoon and back and fourt driving yesterday for a total of about 35 miles with three times parking the car at my destinations.

The car is still unpluged.
Here is what I got:

No stalling or bucking at all
Car ran rough (more like hesitation) on acceleration but no caughing as it did before.

So with this reading? Are we inclined to say my issue is the MAF?
I will continue driving today to see if any of those old issues return.

Thanks
Eric

[jblackburn]

Sounds like you found it!

The car will run rough under acceleration without the MAF because it can only guess how much air is getting into the system based on the throttle opening, and it is doing its best to guess about the amount of gas that needs to be used. And it way over-compensates, I was getting black smoke out the exhaust any time I took off from a stop.

Change it as soon as you can before it takes out the oxygen sensor with a too-rich mixture!

[Volvo_240_Atari_2600]

jablackburn...

Thank you for the tip in the 7th race.
Ran the car since my last post on the 5th w/othe MAF and it ran just like I described,"hesitant on acceleration" w/ slight rough idle but never did it cut out or buck lke it was going to.

Bout a new Bosch MAF sensr from FCP but w/ their snowstorm, priority shipping was delayed (understandable) and I got it yesterday. I replaced it and checked for the code. Came up with one code for the MAF

Cleared the code and went on my way.
On the way home w/ the gas guage just under 12, I topped it off with high octane MOBIL gas and at the gas station the CEL came back.

I checked it and ran the following codes: (6) all together

P0300
P0301
P0302
P0303
P0304
P0305

All are misfires... Cleared them again and so far nothing has come back.
The car seems to run fine w/ no hesitation and or bucking or stalling.

Since I ran it through the limp mode for over a week, any chance these codes are just a fluke?

Like I said, it appears to run fine and will need to run it a few days before I fel safe to hand it back to my wife. Her issue was of course the car stalling all the time.

Thanks
Eric

[jblackburn]

It may help to completely reset the computer's long-term fuel-trim, etc. and have the computer re-learn itself with the new MAF sensor installed. If you get any more running issues, it may help to pull off the battery cable and completely reset the computer. Now that it's working properly again, it might not know how to run correctly, and it's taking it some time to get used to that. If you don't normally use 89 or 93 gas, maybe that's something it was trying to get used to as well.

My advice would be to drive it a few days and not worry about it, and see if any more issues pop up. Any more random unexplainable issues (like the misfires on all cylinders) could be dealt with by a good hard-reset of the computer. But hopefully you've knocked them all out, keep your fingers crossed!