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Old 07-29-2014, 10:22 PM   #1
fullmetal779
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2000 Grand Am SE rough idle problems

I have a 2000 pontiac grand am with a 2.4 L engine it is automatic transmission. Th issue is i just bought the car from a lot thinking it was an easy fix. What happens is when i start the car it goes from a 1k idle to a 500 or lower and sounds like it might die or if i am at a stop light and decelerate too fast it also feels like its going to die and has a few times unless i keep the gas pedal pressed down. I read the codes at my local store they said it was a engine misfire, o2 sensor the front one, and the map sensor. My farther works at a pull and save which is a lot to pull used parts from cars hes brought a used igniton coil, used boots , i bought new spark plugs and nothing was fixed there. we have replaced the maf sensor and the map sensor both with used parts neither fixed the problem. im at my wits end here i cannot afford to take it to the shops around here and am trying to get this fixed to get back and forth to work. Any help is appriciated i may have left out parts that have been replaced please ask also as far as lights are concerned the check engine soon light is on .
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Old 07-30-2014, 01:28 PM   #2
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Re: 2000 Grand Am SE rough idle problems

The O2 and MAP codes could be caused by the misfire....

You replaced the coils? Just the coils or the whole top(coils, ignition tower, ICM and metal top of engine)?
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Old 07-30-2014, 01:51 PM   #3
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Re: 2000 Grand Am SE rough idle problems

Yes I have
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Old 08-19-2014, 01:16 PM   #4
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Re: 2000 Grand Am SE rough idle problems

bump i had looked at it and im still stuck its still misfiring after changing the sensors
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Old 08-19-2014, 08:48 PM   #5
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Re: 2000 Grand Am SE rough idle problems

As I stated before, the misfire could be causing those codes....so replacing the sensors the codes are named after, was not the answer.....

One thing you have to realize....when a code is set, replacing the part the code is named after, is just shot gunning parts without diagnosis.....

For example.....you could have an O2 sensor code....you replace the sensor and the code comes back.....but that code is based on not just the sensor, but also the circuit that the sensor is in, and also, anything that would affect the output of the sensor......for example, a vac leak can skew the data of the sensor......the vac leak is the problem, not the sensor.....

If you have a misfire, you you have a rough idle, especially on a 4 cyl engine....that rough idle will affect the reading of the map sensor.....also, a misfire sends unburned fuel and oxygen into the exhaust....unburned fuel is bad because that catalytic converter is hot to begin with, and adding fuel to it, can overheat it and damage the catalyst.....But O2 sensors do not detect fuel., they detect oxygen......because you have excess oxygen from the misfire entering the exhaust, the O2 sensor sees a lean condition....guess what the computer does? Runs the engine richer......this could contaminate the O2 sensor or skew it's data, causing a code....

You have to take care of the misfire, which should be setting a P0300 code....

Hopefully, the coils and boots you used were ok.....you replaced the plugs....still have the misfire........

Two things to check....engine compression and checking the vac line to the f/p regulator for fuel(ruptured diaphram of regulator)......if both are ok, the number one solution for misfires on these engines is the coil tower........that is the plastic tower, that the coils sit in, and is attached to the metal top of the engine......do not use a used one.....these tend to carbon track.......put a new on on.....on occasion , I have seen an ICM be the problem, but it is rare......if you had a scope, you would see the spacing on the ignition output is not evenly spaced.....

My money is on the tower if those two things check out.....
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Old 08-19-2014, 09:33 PM   #6
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Re: 2000 Grand Am SE rough idle problems

And the tower is the big plastic thing attached to the ignition coil. correct?

Last edited by fullmetal779; 08-19-2014 at 11:49 PM.
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Old 08-20-2014, 07:53 AM   #7
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Re: 2000 Grand Am SE rough idle problems

ill also get those two tests done today and update after
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Old 08-20-2014, 08:41 AM   #8
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Re: 2000 Grand Am SE rough idle problems

Yes....
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Old 08-20-2014, 08:55 AM   #9
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Re: 2000 Grand Am SE rough idle problems

So I was told my car doesn't have enough vacuum the tech put a gage on to my map sensor hose and tested from there saying I wasn't getting enough suction I would imagine that could also be the problem tho he gave no solution on how to fix it
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Old 08-20-2014, 03:19 PM   #10
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Re: 2000 Grand Am SE rough idle problems

So I did a compression test and it was at 175 psi each
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Old 08-20-2014, 07:32 PM   #11
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Re: 2000 Grand Am SE rough idle problems

i found out the mechanic i went to probably had no intention of fixing my car he didnt test it just said run techron through your engine and it will probably get better and shipped me off on my way
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Old 08-20-2014, 08:01 PM   #12
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Re: 2000 Grand Am SE rough idle problems

If your car is misfiring, vac will be low....
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Old 08-20-2014, 08:12 PM   #13
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Re: 2000 Grand Am SE rough idle problems

Oh that i did not know. I was told that my fuel pressure pump is working cause if it wasn't then the car wouldnt even run.

So i guess im back to the start again wondering if its my ignition housing or the coil this is the part we are talking about correct?
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