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2004 Pontiac Grand Am SE 3.4L - Idle Revving, Trouble Starting


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steeledriver
New User

Sep 3, 2015, 7:52 AM

Post #1 of 7 (1029 views)
2004 Pontiac Grand Am SE 3.4L - Idle Revving, Trouble Starting Sign In

Okay guys, this one's been a real pain for me. I've been having trouble with an automatic 2004 Grand AM 3.4L with 325,000 km on it for a few weeks now.

Symptoms:
- Car often will not start without being fed fuel.
- While parked or in neutral, engine swings from 600-800rpm, then the swings grow to 100-1100. This often (but not always) settles down to 600rpm when you put the car in drive. If you leave it in park for a minute, the engine will swing off and die.
- Code reads as P0300 - random cylinder misfires.
- Fuel smells like rotten eggs.
- Car occasionally dies when it comes to a stop, and has frequently died while doing a sharp turn.
- Car sometimes shifts gears at the wrong time while accelerating.
- While on the highway, it may shift down and then back up.
- Surging while driving slowly.

What's Been Done:
- Completely cleaned idle control valve. Tested the valve, and it moves in and out when the car starts. Could still be bad anyway.
- Tested resistance between pins of idle control valve. Approximately 50 Ohms between pins 1-2 and 50 Ohms between 3-4, and all others are open.
- Replaced all spark plugs, checked gap.
- Replaced spark plug wires.
- Cleaned the mass air flow sensor.
- Completely cleaned the throttle body.
- Tested idle position sensor. Getting a supply voltage of 5V, and the wiper to ground voltage ranges from 0.5V when closed to 4.5V when fully open. Smooth transition from closed to open. Seems good.
- Blocked the EGR, no difference.
- Tested the PCV valve - if you remove the valve altogether partially block the hose with your thumb, the engine settles at 600rpm. Replaced with a new valve, still have the same problem.
- Checked for vacuum leaks with propane, none found.
- Replaced the air filter.

Noteworthy:
- If you disconnect the mass airflow sensor and start the car, it idles properly at 600rpm. As soon as it's connected, the engine hunts.
- Putting propane into the airflow after the MAF doesn't accelerate the engine.
- Revving the engine makes it return to 600rpm, but a few seconds later it will begin hunting and spin out.

Any ideas?


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Sep 3, 2015, 8:49 AM

Post #2 of 7 (1022 views)
Re: 2004 Pontiac Grand Am SE 3.4L - Idle Revving, Trouble Starting Sign In

? What was that test on the TPS? It should sweep a range of ohms just by itself and may not. Anything like that a zillion more can set off a chain reaction of poor info to other control and runs lousy. Those misfires are your converter trying hard while killing it too making the odor.


I'm not sure you code readings came out complete and probably should go for a higher end reading than just one code that showed with that much going on,


T



steeledriver
New User

Sep 3, 2015, 9:12 AM

Post #3 of 7 (1017 views)
Re: 2004 Pontiac Grand Am SE 3.4L - Idle Revving, Trouble Starting Sign In

I hooked a multimeter up to the TPS and tested the resistance between and voltage across the terminals. I forget the exact resistances off the top of my head, but it swept smoothly to above 2000 ohms. The voltage reading from the high terminal to ground was 5V, and the voltage reading from the center terminal to ground swept from 0.5 to 4.5 volts smoothly with no spikes.

I had the code read at a mechanic's shop with a high quality tester - their code reader also only read one code - P0300. The problem is symptomatic of the TPS or IAC, but they both seem to be working fine from external tests. That doesn't necessarily guarantee they're working.

A quick scan of forums for things I haven't tried yet yields these possibilities:
- Crankshaft position sensor
- Ignition coil pack
- Fuel pump


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Sep 3, 2015, 9:44 AM

Post #4 of 7 (1012 views)
Re: 2004 Pontiac Grand Am SE 3.4L - Idle Revving, Trouble Starting Sign In

Copies from a site as to what a TPS is doing and what can go wrong...........
">>
  • Throttle position sensors send voltage to the computer to indicate throttle angle
  • When not replaced, vehicle may experience poor idle, pinging, lack of power, inconsistent transmission shift points, rich or lean running, spark plug fouling, poor fuel economy, catalytic converter failure and/or CEL/MIL illumination<<"

  • I didn't find a chart right away to check ohms or volts sent on to computer but it "sweeps" changing ohms is one way on the bench just watch it change from home to its WOT position. Bet it doesn't change at all.


    You said you need to "feed" it fuel to start it. YOU ARE NOT FEEDING IT FUEL IF YOU MEAN WITH YOUR GAS PEDAL IT ONLY ALLOWS MORE AIR THRU which may more closely match the misinformation the TPS is sending along.


    Your code readings can't be good. I think this engine thinks and is delivering fuel and adjustments for one set throttle position righ now? Want a code just unplug it and see it if changes anything AND throws a code,


    T



    Discretesignals
    Ultimate Carjunky / Moderator
    Discretesignals profile image

    Sep 3, 2015, 1:07 PM

    Post #5 of 7 (1005 views)
    Re: 2004 Pontiac Grand Am SE 3.4L - Idle Revving, Trouble Starting Sign In

    What is the fuel pressure while all this is going on? I would revisit the MAF sensor. You will need to measure the frequency of the sensor using a lab scope to see what it is doing while the engine is acting funky. That is unless you can swap a known good MAF sensor to see if that changes anything.





    Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

    (This post was edited by Discretesignals on Sep 3, 2015, 1:10 PM)


    Tom Greenleaf
    Ultimate Carjunky / Moderator
    Tom Greenleaf profile image

    Sep 3, 2015, 7:07 PM

    Post #6 of 7 (998 views)
    Re: 2004 Pontiac Grand Am SE 3.4L - Idle Revving, Trouble Starting Sign In

    Ditto with DS on tests and parts. 325Km = 201,000 Miles so personally I don't find some cheaper items a waste to be new now if you want to go for more. That's about a turning point to me for vehicles for miles/Kms when crap could just start going all over vehicle. You are already at a point of care, luck now. More dependable gets real iffy IMO,


    T



    kev2
    Veteran
    kev2 profile image

    Sep 4, 2015, 9:45 AM

    Post #7 of 7 (969 views)
    Re: 2004 Pontiac Grand Am SE 3.4L - Idle Revving, Trouble Starting Sign In

    first thoughts-
    CODES- will the code reader you are using show ALL codes? P0999 and up?
    FUEL pressure AND then with KOEO observe fuel press drop-
    Try using a vacuum gauge - post results - and @1500 RPM steady watch gauge does it drop?
    you installed new AC DELCO plugs - how did old plugs look, wet dry black tan- might be a clue

    you blocked the EGR- and unplugged the MAF - did those actions set codes?


    (This post was edited by kev2 on Sep 4, 2015, 9:57 AM)






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