05 Cobalt help needed

[rusty ol ranger]

05 Cobalt 2.2L Ecotec 225,000mi

Went to leave the bank this morning, fired it up it acted funny, then all of a sudden went to running real rough, "reduced engine power" came up on dash display, and was down some cylinders for sure.

Limped it 2 blocks (floored at 20mph) to my mechanic...put it on the scanner and got this code...

P0068 MAP/MAF throttle postion correlation

Now for the past month or two its had an issue where when WOT it would start missing and basically shut down at 4500-4800RPM, check engine would blink to signify a "random multiple cylinder missfire" and i noticed i went from 29-30mpg down to 25-26.

But everything else seemed fine...i was gonna throw a fuel filter in it. But didnt get around to it yet as it was only showing an EVAP code and an O2 heater code. It was throwing a cam sensor code and eveidently these cars dont have a cam sensor...its all done through the ignition module...so i replaced that and that code is gone...but the problem persisted.

Anyway my mechanic cleared the codes and it came out of limp mode but now it will not go above 3000RPM without missing. Ive parked it and am gonna put rusty back on DD duty till i figure this out cause im not driving home at 20mph from anywhere.

Anyways...you think its the MAF? Or could it be the Electronic drive by wire throttle? It has a sensor on the pedal as well as the sensor driven motor on the TB itself.

I have very little experence with this newer shit.

 

[RonD]

Yes, P068 means MAF sensors air flow weight reading is not in correct "Range" based on throttle position as shown by sensor, in this case sensor on gas pedal

Clean the MAF sensor first, easy to do

I would invest $15 in a Bluetooth OBD2 Reader
It uses your smartphone or tablet as the display, android or apple
APPS are free or $5

If its offered I would also buy an OBD2 extension cable for $8, as some OBD2 connectors on some vehicles are behind tight panels so plugging in Bluetooth readers can be a pain, not require just an option

With this you can "see" what the computer "sees" from all the sensors
These work on ANY vehicle sold in the US or Canada since 1996, so not a Ford thing or even North American Made thing, ANY VEHICLE, it was/is the Law

You could then watch the throttle sensors data, key on/engine off, while you press down on gas pedal and released it to see if its stable and smooth, no jumping around

MAF sensor data as well, with engine running, you should be able to find MAF data Ranges for your engine size if you search for it
MAF sensor is there to WEIGH the incoming air, "Mass" Air Flow sensor
Computer is already programmed for engine size, so computer already KNOWS volume of air that's coming in at any RPM, its just Math
The air/fuel ratio for gasoline is 14.7/1 and thats a WEIGHT ratio, not volume
14.7 pounds of air to 1 pound of gasoline
14.7grams of air to 1 gram of gasoline

Air weighs a lot less when its warm, "hot air rises" because its lighter, hot air balloons work, fly, because the air inside them is warmer than the air outside, so big difference between warm air and cold air weight
That's the reason for MAF sensors

 

[rusty ol ranger]

Yes, P068 means MAF sensors air flow weight reading is not in correct "Range" based on throttle position as shown by sensor, in this case sensor on gas pedal

Clean the MAF sensor first, easy to do

I would invest $15 in a Bluetooth OBD2 Reader
It uses your smartphone or tablet as the display, android or apple
APPS are free or $5

If its offered I would also buy an OBD2 extension cable for $8, as some OBD2 connectors on some vehicles are behind tight panels so plugging in Bluetooth readers can be a pain, not require just an option

With this you can "see" what the computer "sees" from all the sensors
These work on ANY vehicle sold in the US or Canada since 1996, so not a Ford thing or even North American Made thing, ANY VEHICLE, it was/is the Law

You could then watch the throttle sensors data, key on/engine off, while you press down on gas pedal and released it to see if its stable and smooth, no jumping around

MAF sensor data as well, with engine running, you should be able to find MAF data Ranges for your engine size if you search for it
MAF sensor is there to WEIGH the incoming air, "Mass" Air Flow sensor
Computer is already programmed for engine size, so computer already KNOWS volume of air that's coming in at any RPM, its just Math
The air/fuel ratio for gasoline is 14.7/1 and thats a WEIGHT ratio, not volume
14.7 pounds of air to 1 pound of gasoline
14.7grams of air to 1 gram of gasoline

Air weighs a lot less when its warm, "hot air rises" because its lighter, hot air balloons work, fly, because the air inside them is warmer than the air outside, so big difference between warm air and cold air weight
That's the reason for MAF sensors

I actually do have an OBD2 bluetooth scanner called "Fixd" but i question its accuracy beyond just the codes. It shows the same parameters on freeze frame data for every code.

Anyways...i ordered a new MAF, 22 bucks. I noticed the air box is pretty screwed. I doubt the air filter is doing a whole lot...could be what fried the sensor.

Thanks ron. I didnt know if it was more likely the MAF or something with the goofy drive by wire shit throwing off the maf.

 

[wildbill23c]

I'd say the MAF sensor definitely would be a possible culprit. When those things go haywire they give all sorts of issues, and can cause a lot of misfire problems due to bad data being sent to the ECM/PCM, which would cause too much or too little fuel being delivered. If the air box is in bad shape it'll definitely cause issues with those sensors inline to the intake as it'll be sucking in dirt and debris which will quickly destroy those sensors. This drive by wire stuff really makes for interesting problems too, and to me makes for a very touchy accelerator pedal, as was the case with my 08 Toyota Tundra, man that thing was touchy, and rough roads made it even worse with your foot bouncing off the pedal...it really should have had some sort of spring on it to keep it from being so easy to press down unintentionally.

Wow you managed to put 200K+ on a Cobalt...mine couldn't even make it past its warranty period without a transmission rebuild and the dealer had to do it twice because their incompetent mechanic had no clue what he was doing. Syncros were plastic apparently from what the service manager was saying, they get hot they start falling apart. That car was driven on the highway all the time and couldn't manage to get past 30k without transmission issues WTH, meanwhile the 89 Mazda B2600i 4x4 pickup with 319k on it that I stupidly traded in on that car still runs around town.

I've heard the Cobalts with automatic transmissions were the better choice, wish I'd known that sooner LOL, I got the stripped down base model with manual transmission figuring it would be more reliable, nope, far from it, and all the electrical anomalies that car had made it unsafe to drive at night as the lights would randomly shut off while driving on the highway.

 

[rusty ol ranger]

I'd say the MAF sensor definitely would be a possible culprit. When those things go haywire they give all sorts of issues, and can cause a lot of misfire problems due to bad data being sent to the ECM/PCM, which would cause too much or too little fuel being delivered. If the air box is in bad shape it'll definitely cause issues with those sensors inline to the intake as it'll be sucking in dirt and debris which will quickly destroy those sensors. This drive by wire stuff really makes for interesting problems too, and to me makes for a very touchy accelerator pedal, as was the case with my 08 Toyota Tundra, man that thing was touchy, and rough roads made it even worse with your foot bouncing off the pedal...it really should have had some sort of spring on it to keep it from being so easy to press down unintentionally.

Wow you managed to put 200K+ on a Cobalt...mine couldn't even make it past its warranty period without a transmission rebuild and the dealer had to do it twice because their incompetent mechanic had no clue what he was doing. Syncros were plastic apparently from what the service manager was saying, they get hot they start falling apart. That car was driven on the highway all the time and couldn't manage to get past 30k without transmission issues WTH, meanwhile the 89 Mazda B2600i 4x4 pickup with 319k on it that I stupidly traded in on that car still runs around town.

I've heard the Cobalts with automatic transmissions were the better choice, wish I'd known that sooner LOL, I got the stripped down base model with manual transmission figuring it would be more reliable, nope, far from it, and all the electrical anomalies that car had made it unsafe to drive at night as the lights would randomly shut off while driving on the highway.

To be fair ive only had it since june or july. Paid 400 bucks for it. My buddy bought it for his daughter and when she went to college she wanted something newer....think she ended up with a cruze or malibu. Not sure.

It had a bad miss and needed brake pads. Drove it on the trailer. I cant bitch to much i pry got 550-600 total into it including the purchase price.

Cruise and AC work and it actually runs pretty decent. Its a stripper model with crank windows and manual locks. Just has an auto trans. Ive driven it on a couple 3 hr trips and its never missed a beat and gets 33mpg hwy. 30 running around to work and stuff.

Biggest complaint i have is the lack of power...but maybe a MAF will help. The new ignition module gave it a bit more (itll squeel the tires now lol) down low.

 

[wildbill23c]

To be fair ive only had it since june or july. Paid 400 bucks for it. My buddy bought it for his daughter and when she went to college she wanted something newer....think she ended up with a cruze or malibu. Not sure.

It had a bad miss and needed brake pads. Drove it on the trailer. I cant bitch to much i pry got 550-600 total into it including the purchase price.

Cruise and AC work and it actually runs pretty decent. Its a stripper model with crank windows and manual locks. Just has an auto trans. Ive driven it on a couple 3 hr trips and its never missed a beat and gets 33mpg hwy. 30 running around to work and stuff.

Biggest complaint i have is the lack of power...but maybe a MAF will help. The new ignition module gave it a bit more (itll squeel the tires now lol) down low.

The automatic makes them a bit more sluggish of course, but with a MAF and tune up and probably replace the fuel filter too, it'll wake it up quite a bit when its not misfiring LOL. The little 2.2L 4 cylinder had quite a bit of power it seemed to me, but the Cobalt is pretty small, smaller than my Ford Tempo and Ford Taurus in comparison, I think even a little smaller than the Ford Contour. Never complained about fuel economy with my 06 Cobalt, just the terrible manual transmission apparently they were Getrag brand transmissions, obviously the rejects that VW didn't want so GM bought them, total garbage...the automatics turned out to be the better way to go in the Cobalt. I think the best fuel economy I got was 34mpg on a long trip of all freeway miles from Boise, Idaho to Salt Lake City, Utah and back. It did pretty well, except after the transmission was rebuilt, by the time I got back home, it was doing the grinding between 2nd and 3rd gear, and most times to get the car into reverse and occasionally 1st, I'd have to shut the car off, put it into 1st or reverse then restart the car, horrible transmission, worst manual I'd ever driven, the transmission in the 89 Mazda B2600i 4x4 pickup I had with over 300k on it shifted flawlessly, and my Cobalt I had bought brand new only had 21k on it when I finally had enough of the transmission issues and finally told the dealer to either fix it or come get the car I was done with it, it was under warranty, and they refused to even look at it every time I'd take it in for service. Other than that and the weird electrical issues with the headlights and instrument lights randomly turning off, and the fuel gauge getting stuck on E after putting gas in it...it wasn't a bad little run around car....wish I would have paid the extra $1,000 and got the automatic transmission...one of the somewhat rare cases where the automatic proved to be better than a manual LOL.

 

[rusty ol ranger]

Ok guys need more help.

Replaced mass air flow sensor....runs *ok* (but weak) till about 3500-4k. Then it starts missing to beat all hell, runs like total shit, etc. If i keep the hammer down all it does is wanna stall, if i let off it returns to normal at idle.

No check engine besides the blinking for missfire but i scanned it anyways...

The other code did mention the MAP, wondering if that is what was bad instead of the MAF?

Any input??

 

[snoranger]

Ok guys need more help.

Replaced mass air flow sensor....runs *ok* (but weak) till about 3500-4k. Then it starts missing to beat all hell, runs like total shit, etc. If i keep the hammer down all it does is wanna stall, if i let off it returns to normal at idle.

No check engine besides the blinking for missfire but i scanned it anyways...

View attachment 85535

The other code did mention the MAP, wondering if that is what was bad instead of the MAF?

Any input??

Random misfire at high RPM… I’d check the ign system first. When it starts to get dark, take a spray bottle of water and lightly mist the coils. If you’ve got any kind of voltage leak, you’ll find it. (I didn’t read the rest of this thread) I’d also check your plugs. Are they gapped right and the porcelain isn’t cracked. Start with the basics.

 

[rusty ol ranger]

Random misfire at high RPM… I’d check the ign system first. When it starts to get dark, take a spray bottle of water and lightly mist the coils. If you’ve got any kind of voltage leak, you’ll find it.

Coil pack, plug boots, and module are all new. That was the cause of the inital missfire when i bought it.

 

[scotts90ranger]

Next step is crank sensor, if there's any metal on the snoot of it all bets are off timing wise, it's probably run better than that if the cam sensor had issues but maybe check that too...

 

[rusty ol ranger]

Next step is crank sensor, if there's any metal on the snoot of it all bets are off timing wise, it's probably run better than that if the cam sensor had issues but maybe check that too...

Wouldnt i get a code for a crank sensor? I had a cam sensor code...the ignition module fixed that

 

[snoranger]

Wouldnt i get a code for a crank sensor? I had a cam sensor code...the ignition module fixed that

Not always. If you’re getting the correct signal, but at the wrong time, you may get a misfire without a code… you may get a cam/ crank signal correlation code.

 

[rusty ol ranger]

Ok guys i actually had time to go do some diagnosis today.

I did replace the MAP, 9 bucks and took 15 min.

Either way.

I got the OBD II scanner on my phone and was watching the throttle position meters.

It seems "relative postion" would be the pedal sensor...and "throttle postion" would be the actual throttle body?

Cause when im totally off the throttle the "relative postion" drops almost to zero while the "throttle postion" stays at 25-30%.

If i hammer on it all is well untill i hit about 4500rpm...when "relative postion" stays up around 95% but the "throttle postion" drops to like 60%.

I also noticed that if i run up the RPM without being into it (as in, shifting manually to first and riding it up) it stays smooth till a bit over 5000 before it acts up. But if i floor it under those condtions at 4000 or so it will instantly go to bucking and missing and all sorts of shit. But if i lay off to 3/4 throttle or so it smooth out untill 5 or 5200. at which point i have to go harder on the pedal.

Im really thinking its the throttle body motor or the pedal sensor. What do you guys think?