Question about 2004 Pontiac Grand Am

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2004 pontiac grand am replaced O2 sensor, spark plugs, plug wires and fuel pressure regulator. starts easily. idles very rough. When accelerating car runs well. When cruising on freeway with engine under light load engine misses. Any ideas what to look for? Thanks

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  • ksouthoc Nov 12, 2010

    Randy:

    Please take a look below. I added some additional information. Thanks
    I have a 2004 pontiac grand am. Replaced O2 sensor, fuel pressure regulator, plugs and wires. Engine idels rough starts easy. idle speed is all over the place. When accelerating under load engine runs well. When cruising on freeway with engine under light load engine misses. Sitting at stop light engine idles very rough and you can smell CO inside. Any suggestions?

    Also replaced the idle sensor that controls the air valve position

    NOTE: With engine running I disconnected the plug to the air flow measurement (not sure exactly what it is called) The engine idle speed jumped to about 1500 and engine smoothed out. With engine still running I plugged it back in and the engine speed did not change. Turned off motor and restarted and it was back to a slow rough idle.

    Thank you

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  • Pontiac Master
  • 14,585 Answers

Idle air control motor(IAC). EGR valve. And vacuum leaks to include the brake booster and if you have a plastic intake, that too. this is a start there are other things that will have the same symptoms. let me know
Randy

Posted on Nov 12, 2010

  • 1 more comment 
  • Randy Ohler Nov 13, 2010

    That is called the mass air flow sensor. This could be your problem, but before you change it( high dollar) Was there any codes on the computer, Was the check engine light on. What I woould do is have the codes erased, and start from there. Run the car and when the check engine light comes on , have it checked , get the codes and description. I know some , but there are to many to remember. let me know
    Randy

  • ksouthoc Nov 13, 2010

    Randy:

    the check engine light is on. The code says multiple cylinder misfire. Not other code can be found. i found a MAF on line for about $55 plus freight. When the fuel pressure regulator failed there was gasoline everywhere. When I took off the rubber boot from the air filter to the intake manifold about a cup of gas poured back into the air filter box. Could gas have gotten into the MAF? Is there any way to test the MAF to see if it has failed?

    Thank you

    Kevin

  • Randy Ohler Nov 13, 2010

    This is the way a maf works. the are two thin wires that you can see in the maf. one mearsures the temperture of the air coming into the hole, the other is heated up to 200 plus degrees. the faster the air comes in cools dow the heated wire, thus giving the effect of how much air (in cubic feet per minute) that is traveling thru it. telling the computer, so the computer adjusts the fuel to meet a 14.7 to 1 ratio. If you ave a vacuum leak between the maf and exhaust system it will throw off the maf reading( not pulling enough air) This will cause your random misfires. I have checked many maf sensor codes and have not replaced one yet. The only way I check the maf is against a new one. You can check it with an ohm meter. Check the resistance on each lead, check all leads with all leads. meaning that if there are eight leads comming off the sensor,then you haveto measure it 64 times. the numbers can be off alittle, but not much. Look at the wires that I mentioned and see if they are broken (You may have to use a magnifing glass). If not then I would look for vacuum leaks before I would put out any more money. Also just to say I clean maf sensors with highly flamible liquid, because they can get contaminated with dirt and oil, and this cleans them the best. let me know
    Randy

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Priority Action Part Type Cause
1 Inspect Spark Plug Fouled, Damaged, or Broken Spark Plug(s).
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3 Inspect Wireset Worn, Damaged or Faulty Spark Plug Wire(s).
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---
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Diagnosis and Testing Secondary Spark Test These spark tester looks just like a spark plug, attach the clip to ground and crank the engine to check for spark 91052p10.jpg
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