Help with MAF issue

940 turbo everything stock ran fine yesterday, today I stated it up and it idles horribly, dies sometimes at idle, past 3k rpm it revs fine but below that it sputters a ton. When I unplug the MAF it idles way better but stalls out when I try to drive it. I thought the MAF was bad so I ran to auto zone and got a new one, plugged it in and it didn't change anything. Is there a chance that MAF came bad from the factory or does this not sound like a MAF issue?

I bought one from autozone and had issues with it. Got a junkyard one that worked great after that. Maybe see if anyone is local To you with a known working one you could test with. I’m sure there’s way more experienced guys on here that can help but that was my experience. Autozone failed me on any electronic parts for my Volvo including, alternators,starters and maf. That was a lesson I learned early on. Good luck with the fix

It should eventually throw a code.

The most common issue is airleaks. Spray around with brake cleaner and listen for idle changes

If you really wanna know where all the air leaks are--- smoke test.


I would pull the hose from the air box to the turbo and give it a look for holes.

ZVOLV said:

It should eventually throw a code.

The most common issue is airleaks. Spray around with brake cleaner and listen for idle changes

If you really wanna know where all the air leaks are--- smoke test.


I would pull the hose from the air box to the turbo and give it a look for holes.

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The only code OBD1 will thow is for a bad connection or broken hot wire. OBD1 is useless for diagnosing AMM issues.

There is a section on cleanflametrap web site that tells you what voltages he measured on good mass air sensors. I'd get your voltmeter out and check them referencing that article.

dl242gt said:

There is a section on cleanflametrap web site that tells you what voltages he measured on good mass air sensors. I'd get your voltmeter out and check them referencing that article.

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Anything I've got in that regard is specific to LH2.0 and not applicable to anything Volvo put in a 940 turbo. Even so, the measurements are for the AMM at rest, which is only one data point on a long curve, good for a bet on whether to spend $35 or leave it at the pick'n'pull yards I used to visit 15-20 years ago. They didn't accept returns.

I've always said the only way you can diagnose the AMM is by substitution with a known good one. Good advice was to test and keep an AMM and an ECU for every type of Volvo you own, but that advice is useless after the fact.

Best thing to do is look for false air; vacuum leaks, poor electrical connection, maybe even fuel pressure trouble, and if that fails, find someone with the same engine and fuel system and do some swapping. The resistance measurements purporting to read the hot wire that are suggested in the literature are next to useless.

I just fixed my daughter's car using the rest voltage as a hint the AMM went south, but wasn't confident until swapping in a spare fixed it, and only certain when re-installing the suspect unit broke it again.

First, after checking fuel pressure, I checked the battery supply to the AMM. This is an orange wire on a 91 240. Key on engine stalled.



Next, I check the output voltage the AMM produces without any air flow. On a 240, this is a white/red wire. A gentle tweak of the corrugated AMM hose produces a fluctuation indicating the AMM is responsive. By experience, I've learned to distrust the -016 AMM if it shows much less than 1.4V at rest.



Next, I check the output voltage in our 89 245 just to remind me where it ought to be:



My spare stash is getting low on tested units. Swapped one in -- symptoms gone. Swapped the old one back, symptoms return. By the way, the symptoms on her 91 (380K miles) were it wouldn't idle and only ran at all with a lot of footplay on the accelerator.