Running rough until warm

Tiny
JULIESMITH1
  • MEMBER
  • 1994 CHEVROLET
  • 3.1L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 115,000 MILES
This car was hard to start, then ran rough when it did start. Got to where you could not drive it, did not want to go down the road. Have changed plugs, put on new O2, MAP and TPI sensor. Still running rough until it warms up. Read codes, threw codes 34 and 44. Have not been able to drive long enough to see if those codes still there. Help please.
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Friday, August 5th, 2016 AT 2:07 PM

35 Replies

Tiny
RIVERMIKERAT
  • MEMBER
The code 34 is the MAP Sensor and the code 44 is the O2 sensor reading lean.
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Friday, August 5th, 2016 AT 2:41 PM
Tiny
JULIESMITH1
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How is the lean reading corrected?
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Friday, August 5th, 2016 AT 2:48 PM
Tiny
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It sounds to me as though the MAP sensor is telling the computer to cause less fuel to be injected into the engine. I would replace the MAP sensor first or clean it, and then reset the computer and see if it still throws the code.
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Friday, August 5th, 2016 AT 2:59 PM
Tiny
JULIESMITH1
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We have put a brand new MAP sensor on it already, as well as new O2 sensor and TPI.
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Friday, August 5th, 2016 AT 3:01 PM
Tiny
RIVERMIKERAT
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Ok. Verify that both are the correct part numbers for your truck. Make sure the connections are good and solid. Make sure the MAP sensor is properly installed. Make sure the wiring between the MAP sensor and the computer and the O2 sensor and the computer is good.

Also, have you reset the computer since replacing these parts?
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Saturday, August 6th, 2016 AT 7:39 AM
Tiny
JULIESMITH1
  • MEMBER
No, have not reset the computer. After installing all parts, runs rough until warm. I'm reading articles that says that it could be a MAF sensor, but do not know if a 3.1 even has a MAF sensor. I can't get clear information on that, my Chiltons says for 3.8 motor, but other places say differently.
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Saturday, August 6th, 2016 AT 8:00 AM
Tiny
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What model Chevy is it?
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Saturday, August 6th, 2016 AT 8:20 AM
Tiny
JULIESMITH1
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1994 lumina APV 3.1
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Saturday, August 6th, 2016 AT 8:29 AM
Tiny
RIVERMIKERAT
  • MEMBER
Our reference only lists a MAP sensor for your vehicle. We use Mitchell, which compiles information from the manufacturer.

Do a compression test. Check fuel pressure. I would also run some fuel system cleaner through it. Also check for vacuum leaks.
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Saturday, August 6th, 2016 AT 9:15 AM
Tiny
JULIESMITH1
  • MEMBER
Thank you !
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Saturday, August 6th, 2016 AT 9:24 AM
Tiny
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You're very welcome. Let us know what happens.
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Saturday, August 6th, 2016 AT 10:02 AM
Tiny
JULIESMITH1
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I think I'm losing my mind ! Now it is fluctuating between lean/rich for the O2 sensor ! It keeps going back and forth between the 2 ! What now?
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Saturday, August 6th, 2016 AT 1:18 PM
Tiny
RIVERMIKERAT
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That sounds to me like it's either a wiring or computer problem. Or maybe a faulty O2 sensor. Even new ones sometimes have problems.
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Saturday, August 6th, 2016 AT 2:18 PM
Tiny
JULIESMITH1
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Hush ur mouth ! :-) I'm so darn upset I don't know where to look/check next. Suggestions? P.S. This didn't happen until we ran Sea Foam thru both fuel tank & injectors on top of motor.
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Saturday, August 6th, 2016 AT 2:37 PM
Tiny
JULIESMITH1
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Until we did that, it only still read lean.
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Saturday, August 6th, 2016 AT 2:38 PM
Tiny
JULIESMITH1
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How do you do a compression check? I have a fuel pressure testing gauge available to use but no idea of where hook up for it is located. We have to get this going soon as other vehicle we own has other problems and I'm worried it will go down soon as well. We both depend on it to get to work (different shifts). :-(
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Saturday, August 6th, 2016 AT 4:10 PM
Tiny
RIVERMIKERAT
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Compression is the amount of pressure built up in the cylinders when the piston moves up. To test it you remove a spark plug and crank the engine over. I also like to disconnect the coil to keep the engine from starting. You have to test each spark plug/cylinder. You can borrow a compression tester from places like Autozone and Advanced.

Look for what looks like a tire valve near the throttle body/fuel rail. That's where you check fuel pressure. You should carefully bleed some of the residual pressure off (like throw a towel over the valve first to prevent spray all over) before hooking the gauge up.
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Saturday, August 6th, 2016 AT 5:01 PM
Tiny
JULIESMITH1
  • MEMBER
Codes as follows: 22 1/4 TP volt low reading is.77-.80
24 2/4 VSS no signal
33 MAP sensor high reading is 29 KPA volts.97-.99
45 O2 high volts reading is.07-.99
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Sunday, August 7th, 2016 AT 9:41 AM
Tiny
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Were you able to find a compression tester?
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Sunday, August 7th, 2016 AT 11:14 AM
Tiny
JULIESMITH1
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No. We can't even get the van out of the yard and the other car scares us enough (tie rod ends, resonator and a code for exhaust problems) that we keep it within a 10 miles radius. The nearest auto zone is 25 miles away.
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Sunday, August 7th, 2016 AT 11:25 AM

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