P0300, P0171 and Vacuum Leaks

[twdmar]

Hey everybody,
I just replaced the lower intake gasket and upper intake plenum and gaskets on a 98' monte carlo with the 3800. Just a couple days ago it developed a rough running condition. I pulled up a code indicating the MAP sensor was bad as well as p0300 random misfire and p0171 lean bank 1 code.
I replaced the MAP sensor and that code went away. I pulled the MAF sensor and cleaner it. I pulled the EGR valve off and sprayed a little carb cleaner in there.
I also looked around for vacuum leaks. One showed up where the throttle body attached to the upper intake. The lean condition makes sense with the vacuum leak. The car ran fine for a couple weeks after the intake replacement before this rough idle appeared. After cleaning the MAF and spraying off the EGR, the roughness is only apparent at idle. Is there a reliable way to test the EGR valve with common tools? Also, could a vacuum leak cause a sudden change in the way the car is running?

[maxwedge]

Yes, and make sure you have both o rings in place under the map sensor where the pcv mounts. A bi -directional scanner is the usual way to test the egr, it can be done using a wiring diagram to ground the proper wires at the egr. BTW I am moving this to the MC forum below.

[twdmar]

The MAP and PCV should be put in and sealed properly. The haynes manual states that the egr can tested with an ohm meter which doesn't seem totally correct to me. Can the EGR be tested by putting 12V to it? How about plugging the EGR passage momentarily to determine if it richens up my fuel mixture?

[maxwedge]

The egr can be tested by grounding the proper terminals do not jump 12v to the egr, it has 12v all the time the pcm grounds certain terminals.

[twdmar]

Thanks Max. I have changed plugs and wires, and sealed up any possible vacuum leaks. I checked resistance in all the fuel injectors and all were very close. Each plug for the injectors also had the same voltage. I then ran the engine and disconnected each injector. When removing the #1 and #4 the car's performance didn't change. Seems like likely culprits to me. Is it worth running any more tests?

[maxwedge]

See if those are the paired cylinders on the coil pak.

[twdmar]

They were the same cylinders on the coil pack so i switched a couple of the coils around. Car still ran the same, then i tried disconnecting the fuel injectors. Again, it was the same cylinders as before i switched the coil packs.
I then pulled off the fuel rail and switched each fuel injector on the problem cylinders with one that was unaffected before. Again i ran the car and tried unplugging injectors. Same result as before all the switching, no change when the number 1 and 4 cylinders had their injectors removed.
I also tried running the car without the number 1 and 4 wires attached to the coil and the car ran the same as before. I have pretty much resigned myself to taking it in to the dealer.

[maxwedge]

Do you have spark to those plugs?

[twdmar]

I didn't have anyone to help me check for spark earlier but i did just check them for spark and found none. Its possible that its the ignition module or the computer. Maybe the dealer can figure out definitively for me.

[maxwedge]

When you switched the 1/4 coils around you still had a miss because you still had no spark, sounds like a bad coil no?

[twdmar]

When i switched the coils, the dead cylinders did not migrate. Switched out the ignition module with a new one, checked the resistance on the coils and popped everything back in. The motor is running smooth again.

[nycemsmedic67]

also dont forget the vaccume lines from the throttle body that commect to the fuel pressure and evap perge. that was a pain for me took forever to get it