Car stall when MAF plugged in? '98 V70

Post by **bmdubya1198** » 03 Jul 2017, 10:22

I've been tracking this random miss/sputter since I first started driving this car, and I think I'm down to two things now.
I have an older thread about the issue here for further details if anyone cares to read: viewtopic.php?f=1&t=79374

Anyway, I just ordered a Bosch fuel pump (got a killer deal on Rockauto... $16 before shipping!) and that should be here sometime this week. I thought up until now that's what has been causing this problem, being that the car has 178k miles on it and it was sitting for almost a year before I bought it, then a couple months after I bought it. And before someone hounds me, yes, it's the OEM Bosch 69693.
But a little bit ago, I thought just for the hell of it, I would disconnect the MAF sensor and see how it runs, being that that's one thing I never actually "tested" other than cleaning it a couple times before. I had the car running, it was warm since I had been driving it, and I disconnected the MAF. Idle surged a very slight bit (less than the typical ~500 RPM surge it has) and it steadied out. It ran the same, if not better than before. CEL came on, of course, but it was running and revving fine. I plugged it back in and the car immediately stalled. I got in and started it back up and it took a second, but it ran alright after that.

So what I'm asking is if this is normal, or could this be a sign of a bad MAF? I'm almost certain this one is original, and I know they tend to go bad on these cars.
I'm still going to replace the fuel pump because I know it'll need it sooner or later anyway with almost 180k miles.

obayha · Post by **obayha** » 03 Jul 2017, 12:07

Mine did that for a while. Took three MAF's to get one that worked. Still have the one off the '98. You can borrow it to see if that is it before buying one. They are not cheap. It is a Bosch and I think should work on yours.
Came off my V70 T5.
Shane

Post by **bmdubya1198** » 03 Jul 2017, 13:56

obayha wrote: ↑03 Jul 2017, 12:07 Mine did that for a while. Took three MAF's to get one that worked. Still have the one off the '98. You can borrow it to see if that is it before buying one. They are not cheap. It is a Bosch and I think should work on yours.
Came off my V70 T5.
Shane

I had a feeling the MAF had something to do with this. Like I said, I don't know why it took me so long to bother checking it. I think I might get one from the junkyard, although it is a bit of a gamble with a part like that.

Post by **abscate** » 04 Jul 2017, 05:01

Unplugging electronics while powered up generally not good for them and not a good diagnostic.

Turn car off , then disconnect or reconnect

Without a signal from the MAF, the ECU runs in a default table of fuel injected per engine rpm. If it runs okay without MAF, but not with, there are still many possible failure modes.

Post by **erikv11** » 04 Jul 2017, 22:54

If you test it the way abscate describes, and it runs better unplugged, the problem is either a bad MAF (most usually) or unmetered air getting in after the MAF (sometimes). Swapping in a MAF from the junkyard (or from obayha!) is the easiest way to test, IMHO.

Post by **bmdubya1198** » 05 Jul 2017, 07:16

I'm away for the rest of the week, but I'll check on that when I get home. Maybe the fuel pump will fix it, but if not, I think I have an idea of what else is wrong.

Post by **bmdubya1198** » 18 Jul 2017, 17:13

Replaced the fuel pump and it's been running alright, but now the car has developed an intermittent pulsing idle when warm. It's only when it's in park, but the idle goes up and down between probably 800-1100 RPM. Not constantly, but every couple seconds it'll surge, sometimes to as low as 600 RPM.
I've only experienced one little hiccup since changing the fuel pump (while coming to a stop like it has always done), which is not good enough for me to call fixed.
I tried running with the MAF unplugged, and it runs the same. The problem is when I went to test it, it was running well. I drove it, got it up to temp, and it idled just fine (as always when you're trying to test something). Turned it off, unplugged the MAF, started it up, and it ran exactly the same. I have NOT been able to replicate the pulsing idle with the MAF disconnected.
Unfortunately this issue is intermittent, and it's very hard to test anything. I can't know for sure if I stop the engine and start it back up after unplugging/plugging in the MAF that it will still have the pulsing/surging.
Anything else I can check, or is there a way to test the MAF sensor other than using a known good one? My only other ideas are O2 sensor and IACV. I had an issue after cleaning the IAC back in February where when I put the car in park it idled at probably 1,200 RPM. I fixed that by cleaning it and "unsticking" it (I think a brush bristle had gotten stuck in the valve). So that doesn't need to be cleaned.

Post by **abscate** » 19 Jul 2017, 04:20

Can you monitor fuel trim on your scanner when the problem comes back? Might lead to Volvhanna

Post by **erikv11** » 19 Jul 2017, 04:55

bmdubya1198 wrote: ↑18 Jul 2017, 17:13 ... I have NOT been able to replicate the pulsing idle with the MAF disconnected...

If this continues to hold true, you don't need another test. How long does it usually go without a surge? I would unplug it in the morning and drive it all day (or two) unplugged, you're not going to burn any valves from a couple days of running rich. To be fair though, a bad MAF more usually stumbles randomly, independent of idle speed. But it's a cheap test!

I have never had a problem with a P80 junkyard MAF, you can safely expect almost all of them are good. Well, any Bosch MAFs from the JY.

Post by **bmdubya1198** » 19 Jul 2017, 07:26

abscate wrote: ↑19 Jul 2017, 04:20 Can you monitor fuel trim on your scanner when the problem comes back? Might lead to Volvhanna

I can do that at some point today. I need to reseat an axle seal at some point this morning, then I will get onto that.
I know my fuel trims were all over the place last week right after I changed the fuel pump because the pump wasn't sealed all the way. P0455 has since disappeared, but I haven't re-checked fuel trims.

erikv11 wrote:If this continues to hold true, you don't need another test. How long does it usually go without a surge? I would unplug it in the morning and drive it all day (or two) unplugged, you're not going to burn any valves from a couple days of running rich. To be fair though, a bad MAF more usually stumbles randomly, independent of idle speed. But it's a cheap test!

I have never had a problem with a P80 junkyard MAF, you can safely expect almost all of them are good. Well, any Bosch MAFs from the JY.

Good to know, because I'd rather not pay for a new one!
Like I said, it's intermittent, very unpredictable. It didn't do it at all yesterday, but Monday it happened twice. It's usually when I get home and put the car in park that within probably 30 seconds it begins surging, at which point it's constant until I start the car the next time.