02 pontiac grand am with p0305 code

Im having trouble with my 02 pontiac grand am 3.4 engine. It started idling rough and then the the rpms would go down and then level out every couple of minutes and it is hard to start and the engine would stumble. I had no engine light on so it was hard to tell what was wrong. I changed out the MAF sensor and the pcv valve and, now the idle is normal and it starts good when its cold., the p0305 code came on and off after those changes now i checked the spark plugs and the coil for spark and changed out the wires and the light came off but the car still has a hard start and stumbles after it reaches its running temperature especially after 5 minutes of being parked. I suspect that it its an oxygen censor because it gives off a little smell of sulfer but it might also be an injector. will an oxygen sensor make the car have trouble starting and cause it to stumble? the car runs great after it starts.

I think that an o2 could do that but i would check the compression on that cylinder and see about changing the plugs and wires how long have they been on the vehicle for? it could be also a dirty injector check the injector pulse and clean them with fuel injector cleaner also check for burned valves intake leaks

I was reading on another post that it might be the o2 sensor so im going to try that next. I recently changed the plugs and wires so it wasnt that. If that doesnt work then im going to check my injectors. Thanks for the reply.

You are very welcome and if its not the injectors then i would try either the coil going to #5

Check the fuel pressure regulator it could be leaking this would cause a hard start when cold and after it sits for a while.

pull the pvc tube off the valve cover with it running an see if there is a vacume at the valve cover hole with your finger.if yes then check for bad intake gasket,that will cause the same simtoms you describe. if not you will have to look for other problems.
good luck

Ok today I changed out my fuel filter checked the fuel pressure reg for leaks and i disconnected my o2 sensor and drove around started the car to see if i noted any changes. nothing worked! I had already checked my pcv valve for vacum and its good and i also replaced the hole tube. now im ruling out that its the injectors or a leak in my intake gasket cause i do have a pinging sound that sounds like a lifter. Oh! and it starts hard cold or warm now with a stumble.

Check the compression and see what that is then the #5 injector or it could be a fuel regulator also an intake leak indicatication of an intake gasket also check the condition of the valves and the valve springs

I am trying to fix this problem before I have to do any major work like remove the intake. cause I dont know my way into the engine so I will have to take it to the shop. Im going to try an injector cleaner and if that doesnt work then to the shop I will go.

Since my last post i have taken the car to the shop all they can tell me was that everything looked good but they would service my TB for $200. I took it home tested and serviced my Iac and TB. The car turns on good when cold, and runs good at operating temp. Once i park and leave it for about 20 to 30 min it will have a hard start and the idle will be at about 650 to700 rpm on park then the idle will drop and go up and down trying to level out till it stalls or levels out. it will do this every couple of minutes but it only does it on park not while on drive. any SUggestions?

The smell is Hydrogen Sulfide, as an educated guess, your Catalytic is going bad. You can get random misfires, EGR Codes, or Cat not reaching operating temps along with rough idle loose of power, slight over temp like 220 F or so, no acceleration and many other issues with plugged up Converters, sometimes not even a code!

I am guessing that you have the 3.4 V6 on it.

I heard several ways to test it, take the O2 Sensor off and start the car so gases can escape and reduce the back pressure, other is to drill a hole before the Cat and if that not is the issue, place a Self Tapping screw to plug it up. Another is replace the Cat but that could be expensive, like $65 to $200 depending which one you buy plus labor if a muffler shop does it. For an old car I recommend the $65 that all you need to do is cut the old one and weld the new one so you need some to weld with, the other, you need to unbolt the Cat and you can shear a nut or stud at the manifold and you are going to have a world of trouble for that.

Now, Cats does not fail easy, excess oil, fuel and Glycol can destroy a Cat. On these cars they have the bad tendency to have Lower Intake Manifold gasket leaks, that means, that some Glycol can get to the intake manifold and get sucked in the combustion chamber and hinder the combustion on one cylinder. the water galleries are on the corners of the Manifold, the 5th Cylinder is the last one on the bank. If Glycol gets there even in small amounts, little by little will plug the Cat.

There is class action suit on leaking LIM Gaskets, so you might get a refund on the repairs. Call few dealers about it.

Now you have 2 issues to investigate... good luck !

Today I changed out my upper 02 sensor changed out my coils cause i got a p0300 code and I tried the hole in the cat trick and nothing worked the car still does the same thing. Im thinking maybe it has a vacum leak or the egr valve . Ay suggestions?

How the exhaust smells like, does it have a weird smell? If is a leak, I can say the Lower Intake Manifold gasket is the one to blame.

Is weird, I had the same code and the EGR Malfunction on my Grand Am and the Cat was the one to blame.

but if its a leak then why does it do it after the car is warm and has been parked for 20 min wouldnt it do it on a cold start also? I have to let the car sit for 20 min off then turn it on for it to do this. I also tried what cricket said about pulling the pvc and check for suction from the valve coverand i didnt have any so i take its good. I also changed out my egr valve and nothing! no changes. Tmrw im going to change out my coolant temp sensor, hope it works!

Of course, no vacuum from the valve cover, just from the manifold.

As far temps, metal expands and contracts with heat and pressures.