2003 Chevy Impala possible MAF sensor malfunction

Tiny
NBEAM
  • MEMBER
  • 2003 CHEVROLET IMPALA
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 204,000 MILES
My car randomly has engine surges/stumbles that, once they begin, will get worse and eventually become so severe that it will stall. I have to try and try to get it restarted and then limp home. Sometimes the car is better the next day, sometimes in two or three days. Then I can drive it again, but sooner or later the trouble starts again, usually within about 50-60 miles of mostly highway driving. There is no check engine light and no trouble codes even when it cuts off. I have changed the fuel and air filters. It passed all the fuel sys and vacuum tests I did on it, even when having the problem so bad I would sometimes have to restart it to continue the tests. I suspect a bad MAF sensor, but can't prove it. When running, none of its numbers seem noticibly off on my scan tool. However, I get readings from it when the engine is off and the key on--when I assume it should read 0.0 like my Mazda and Toyota. It usually scans betwen.2 and.5 lb per min with teh engine off, but has given readings of 6.4, 11.7, and even 20.4 (not accurate even if I was running 100 mph). The reading stays steady as long as I have the key on, but turn the key off and then on again and the reading changes to another random number. Crank the car, and it goes to normal idle numbers like.4 to.6 lb. This continued even after I cleaned the sensor wires. Are the false engine-off readings a sign of a bad sensor or is there another problem with the car?
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Saturday, April 11th, 2009 AT 3:55 PM

6 Replies

Tiny
JAMES W.
  • MEMBER
From your description I would have to lean towards a bad mass air. When the engine seems to be running normally, had you tried giving the MAS a rap with a screwdriver?
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Saturday, April 11th, 2009 AT 10:57 PM
Tiny
NBEAM
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Yes, I tried the screwdriver thing. It did not seem to affect the way the engine ran or the scantool readings with the engine on or off. That was one of the reasons I still wasn't sure if the sensor was bad or not. Unplugging the MAF also did not affect the running as far as I could tell, but I did not drive it like that, just revved it in park.
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Sunday, April 12th, 2009 AT 6:33 AM
Tiny
JAMES W.
  • MEMBER
My wife drives an '04 Impala and just for the heck of it I tested her MAF and at a warm idle it read.55 and with key off it was 0.0. And her car runs great.
Everything you describe points to MAF and if I were in your shoes, I'd change it. Keep in mind, we can't rule out the ECM here either, but that's usually the last thing I blame. Let me know.
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Sunday, April 12th, 2009 AT 12:52 PM
Tiny
NBEAM
  • MEMBER
Thanks so much for the info. Since your wife's reads 0.0 with the key off, I've got a replacement MAF on the way. Will let you know how it goes in a few days when I get it on and test drive it.
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Sunday, April 12th, 2009 AT 8:04 PM
Tiny
JAMES W.
  • MEMBER
OK, let me know how it goes. I can always use the info to pass onto others.
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Sunday, April 12th, 2009 AT 8:15 PM
Tiny
NBEAM
  • MEMBER
Sorry, it took so long to get back to you on this, but its been an interesting time with the car. I got the MAF changed no problem and it ran fine for about 200 miles, then had the problem again and died on the way to work. Couldn't get it home this time and so I had it towed to a shop. Figured they could diagnose it while it had the problem. They said ECU bad so replaced it. Once they replaced it, found that crank sensor wire had gotten against the rear exhaust manifold and melted and shorted. Said that killed the ECU. Not sure about that last part. I can believe the bad crank sensor caused the performance problem and may have sent a reading to the ECU that told it to go into limp home mode, but kill it? Shouldn't it be tougher than that or blow a fuse or something first? Maybe they just told me that cause they already had the new ECU in the car. Anyway, picked it up yest, drove it 90 miles today and it ran fine for 50. However, while doing some in-town driving, the check engine light came on. Set two of the same code for catalyst not performing at peak efficiency. Think it set them when the catalyst monitor ran first time after reset, but not sure. I reset it with a scan tool and it hasn't come back in 40 miles of driving since. I can't tell if this is related to the prior problem. I am a little afraid it ran so poorly (very rich at times) or shook so violently (it was REALLY shaking hard when it malfunctioned) when the ECU went that it damaged the catalyst. Or it could have nothing to do with any of that or just be an O2 sensor. Got to love 200K cars.... So, that is the update. If you have any thoughts, let me know. Otherwise, I hope this helps someone else.
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Thursday, April 30th, 2009 AT 10:41 PM

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