Posible Mass airflow sensor
Thread Starter
Heel & Toe
Joined: Jan 2013
Posts: 16
Likes: 0
Posible Mass airflow sensor
My car went from running strong with no signs of problems to acting like it's not running on all cylinders. All this in a matter of several minutes. It began with just a slight roughness to loosing considerable power, enough that the car would not drive. I shut it off and let it sit for 10 to 15 minutes and restarted it. Although it ran rough I managed to drive it a couple of miles. The rough running went from mild to slowly losing all power again. I repeated what I did again and managed to drive the 1/4 mile to my home. My mechanic feels that the problem is the Mass Airflow Sensor. Is what I wrote sound like that's the problem?
Last edited by mroxford; Jul 15, 2014 at 11:21 AM. Reason: sent the thread unfinished by mistake.
Team Owner
Joined: Sep 2001
Posts: 62,139
Likes: 1,727
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
First, what year car.
2nd, are there any SES lights? We need to know if theres a code set. If its dropping into Limp Home mode the Code should be set.
2nd, are there any SES lights? We need to know if theres a code set. If its dropping into Limp Home mode the Code should be set.
Thread Starter
Heel & Toe
Joined: Jan 2013
Posts: 16
Likes: 0
Thank you for responding. It's 1989, the ck engine light did go on when I drove it. The mechanic told me the light is not on now. No code is showing.
Pro
Joined: Mar 2009
Posts: 702
Likes: 259
From: Middletown Delaware
I get concerned when mechanics start to 'feel' and 'sense' a bad sensor. There is only one way to do it right... find evidence to the problem and then replace what is defective. Especially someone who is supposed to be a 'professional'!!
Instructor
Joined: Oct 2013
Posts: 213
Likes: 23
From: Fond Du lac Wisconsin
MROXFORD, My 90 coupe has gone from running perfectly to limping along on 5 cylinders and then back to running great in the last 3 days. I explained the symptoms to a local C4 repair shop. He is 99% sure that the mass air flow sensor is simply dirty based on his experience with multiple 90 Corvettes. Car is going in for a $26 cleaning later this week and he will read the codes . The engine service light is not on. Injectors, plugs, wires were replaced 18 months ago, along with a new fuel pump last week. If the unit is bad, the replacement cost is $200. Did you check for any "arc'n unt der spark'n" under the hood in a dark garage? The under hood light fuse is the top left one.
Team Owner
Joined: Sep 2001
Posts: 62,139
Likes: 1,727
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
First thing to do then is drive it until you see the SES light come on, or simply let it idle up to operating temperature. It'll drop into closed loop operation.
It should then set an SES light as it sees something is going on with the MAF voltages. You need to pull the code right then. Likely it is Codes 33-34-36, all or a combination of them, if it is MAF-related. You can get a code reader, or use the paperclip trick. A search in the archives will show you how to do the trick.
Then there are procedures in the manual to sift out the culprit. It could be the MAF, in which case you need to replace the relays (behind the battery) as well, or simply the relays. It could be something completely different, but you have to pull a code to know where to go.
Do not throw $200-300 at the problem, pull the code.
It should then set an SES light as it sees something is going on with the MAF voltages. You need to pull the code right then. Likely it is Codes 33-34-36, all or a combination of them, if it is MAF-related. You can get a code reader, or use the paperclip trick. A search in the archives will show you how to do the trick.
Then there are procedures in the manual to sift out the culprit. It could be the MAF, in which case you need to replace the relays (behind the battery) as well, or simply the relays. It could be something completely different, but you have to pull a code to know where to go.
Do not throw $200-300 at the problem, pull the code.
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 412
From: WV
Vader is correct, 
these are not the cars you want to start throwing parts at, there are to many things that could be causing this problem to just guess... You need to eliminate possible causes one at a time...This is the only way to find whats causing your problem...It could be the MAF sensor, but it could also be the coil, ICM, or any number of other things...Hooking the car up to a scanner is the first thing your mechanic should do, he could check the readings on the device and see if anything was off spec...Using a scanner you can see how many grams/sec of air the MAF sensor is reading at the different rpms, and see if the sensor is working correctly.The Maf sensor reads from (0 to 255) grams/sec when operating normally, if the maf sensor isn't working smoothly within this range, then you have a bad sensor.....WW
these are not the cars you want to start throwing parts at, there are to many things that could be causing this problem to just guess... You need to eliminate possible causes one at a time...This is the only way to find whats causing your problem...It could be the MAF sensor, but it could also be the coil, ICM, or any number of other things...Hooking the car up to a scanner is the first thing your mechanic should do, he could check the readings on the device and see if anything was off spec...Using a scanner you can see how many grams/sec of air the MAF sensor is reading at the different rpms, and see if the sensor is working correctly.The Maf sensor reads from (0 to 255) grams/sec when operating normally, if the maf sensor isn't working smoothly within this range, then you have a bad sensor.....WW
Last edited by WW7; Jul 15, 2014 at 09:53 PM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
Instructor
Joined: Dec 2013
Posts: 100
Likes: 20
From: Port St Lucie Florida
MROXFORD, My 90 coupe has gone from running perfectly to limping along on 5 cylinders and then back to running great in the last 3 days. I explained the symptoms to a local C4 repair shop. He is 99% sure that the mass air flow sensor is simply dirty based on his experience with multiple 90 Corvettes. Car is going in for a $26 cleaning later this week and he will read the codes . The engine service light is not on. Injectors, plugs, wires were replaced 18 months ago, along with a new fuel pump last week. If the unit is bad, the replacement cost is $200. Did you check for any "arc'n unt der spark'n" under the hood in a dark garage? The under hood light fuse is the top left one.
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 412
From: WV
May be time for a new mechanic....
Le Mans Master
Joined: Jul 2004
Posts: 6,224
Likes: 697
From: Clifton Park, NY ............Clearwater, FL ... 85 Original Owner
My car went from running strong with no signs of problems to acting like it's not running on all cylinders. All this in a matter of several minutes. It began with just a slight roughness to loosing considerable power, enough that the car would not drive. I shut it off and let it sit for 10 to 15 minutes and restarted it. Although it ran rough I managed to drive it a couple of miles. The rough running went from mild to slowly losing all power again. I repeated what I did again and managed to drive the 1/4 mile to my home. My mechanic feels that the problem is the Mass Airflow Sensor. Is what I wrote sound like that's the problem?
Pro
Joined: Oct 2012
Posts: 672
Likes: 2
From: Cheltenham, England
Don't forget, it doesn't have to be the sensor itself, it's just as likely to be the wires or plugs that connect to it,they can get brittle and fracture inside the insulation, when I fitted my new MAF I fitted new connections at the same time, just for peace of mind.
Le Mans Master
Joined: Dec 2006
Posts: 5,139
Likes: 482
From: H-Town Texas
I'll start off by qualifying that I'm more in tune with the LTx cars than the L98 cars. That said...
Typically anything related to intake and exhuast sensors will throw a code pretty quick. Along with misfires etc.
I would be a little leary of a mechanic that does the "I have a hunch" diagnosis, or at least of that diagnosis. Granted, maybe he's seen this before, but he should also know that there are a plethera of systems on a car that could create similar symptoms. It's like going to your doctor for knee pain, and before you even sit down he says you have a pinched nerve in your neck.
It could be the maf, it could be the distributor, it could be the fuel pressure regulator, it could be the fuel pump, it could be a bad spark wire or plug, it could be a clogged catalytic converter, it could be a valve train issue, it could be the timing chain, it could be a head gasket, it could be the ecm, it could be bad gas... I think you get the point.
Typically anything related to intake and exhuast sensors will throw a code pretty quick. Along with misfires etc.
I would be a little leary of a mechanic that does the "I have a hunch" diagnosis, or at least of that diagnosis. Granted, maybe he's seen this before, but he should also know that there are a plethera of systems on a car that could create similar symptoms. It's like going to your doctor for knee pain, and before you even sit down he says you have a pinched nerve in your neck.
It could be the maf, it could be the distributor, it could be the fuel pressure regulator, it could be the fuel pump, it could be a bad spark wire or plug, it could be a clogged catalytic converter, it could be a valve train issue, it could be the timing chain, it could be a head gasket, it could be the ecm, it could be bad gas... I think you get the point.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
No code is showing.
If you/he thinks it's a MAF issue see if you/he can find a good MAF from a mid-late '80s F-body car for a swap.
Another item to check is fuel pressure.
Last edited by 65Z01; Jul 16, 2014 at 09:07 AM.