Running rough on initial start

[L82shark]

In the morning or anytime the engine is cold, when you start her up the motor runs really rough, missing, like its running on 4 cylinders for about 30-45 seconds. Then it smooths out. No codes anywhere. Any ideas?

[sethjamesrimrodt]

Mine ran really rough when it had a vacuum leak. Look on the top of the valve covers where the hard plastic lines are attached. My rubber couplers were dried out and leaking. Be careful all the plastic is very fragile. Mine still runs rough at times, it runs like a camed 350.

[CMNTMXR57]

Some roughness is normal on an open loop cold start. If it goes away as it runs/warms up, Doesn't trigger any misfires (which would command your MIL on), I wouldn't sweat it.

[L82shark]

ok, now it will trigger the occasional misfire code and throw the SES on. Any ideas? Runs really rough for about 30-40 seconds, then smooths out fine. Its like the choke is sticking closed if was a carb car. I'm not real up to date on the Northstar fuel injection.

[dpnewfie]

You might have a coil going out. How is the car under load? Take it out and do a quick WOT. If a coil is going bad the SES may flicker and the engine may stumble a little.

Another thing to try would be a bottle of Techron on your next fill up.

[L82shark]

You might have a coil going out. How is the car under load? Take it out and do a quick WOT. If a coil is going bad the SES may flicker and the engine may stumble a little.

Another thing to try would be a bottle of Techron on your next fill up.

that may be it. I nailed it a few times a week or so ago and once or twice I had the SES light up temporarily. How do you check to know which one if its intermittent?

[CMNTMXR57]

Bad coil or cracked plug. If it's intermittent, I don't think it could be anything in the feed from the PCM (the main harness it all plugs into). There isn't much to these ignition systems. It is a coil pack module all in one, that upon tightening down, caps over the plug directly (It has a spring loaded contact inside that adjusts to the plug end), and perhaps that's broken.

This of course is predicating that it is ignition. It could be fuel also. Could be something as simple as bad or watered down fuel, a bad/plugged injector, low fuel pressure, etc. If you can get the misfire code (it should throw a generic P0300 and then a cylinder P030x for the specific cylinder(s), causing the problem, that would help point one down the right road. We'd always get this with low quality fuels (Citgo for example), especially during the winter months with RFG fuels. Before doing an injector balance test, we'd pour in some GM fuel system cleaner (relabelled Chevron Techron), in the tank and if the problem didn't come back, problem solved.

Try running some Chevron Techron or even Sea Foam.

[L82shark]

I have gotten the P0300 code, but no others. Been running Shell fuel in it only. May switch it up if I can find another non-ethanol brand close.

[sethjamesrimrodt]

Well I got a p300 code when my coil was bad, I never got the p30X code.

[Bill's GXP]

I got the dreaded SES code this morning upon start up. As soon as it started, I knew something was amiss. (no pun intended) The SES was blinking which told me that there was a miss somewhere. It was running rough, to say the least. After work I headed to Autozone to have them pull the code. He said it showed an intermittent miss on cyl #4. They wanted $266 for a Chinese branded set of coils. I told him thanks but I'd burn the car before I put Chinese parts on it. I went online an bought an AC Delco coil pack D593A for $115. I'll get them Wednesday and swap them Sat. BTW, car has 57K in mileage. I'll do spark plugs at this time too.

[CMNTMXR57]

They're all made in China, even the GM parts, but you have the GM piece of mind at least. These are a coil module setup that includes a spring loaded adjuster in the tip of the module that accomdates the plug. I bet that is where the fault is in the original. It's not serviceable really. Today's stuff is "modular" and meant to be R&R'd.

[Bill's GXP]

Just to make sure, the factory plugs were iridium. Right? I'm going to do the even bank now and then the rear odds in a few weeks. Thanks for the help. BTW, is there a Youtube video for replacing the coils? If anyone has a direct link that would be great. Thanks.

[CMNTMXR57]

Platinum. AC Delco 41-987 I believe. No YouTube videos. This is pretty easy to replace. Pull off the engine cover, disconnect the electrical feed to the second coil pack from the passenger side on the front bank, remove the two torx bolts holding it down, remove. Be mindful of the little green rubber sleeve that sits between the bracket that the coil mounts to, and the cam cover. It helps seal off the coil from the outside elements.

[Bill's GXP]

Thanks. Did the job in about 45 mins. Car runs great now. Cleared codes and we're off to the races. The rear plugs look they are gonna be fun. What is that module? just above it with the black hose running to it? Does water run through this? What is procedure for removing to do plugs? Thanks in advance.

[CMNTMXR57]

EGR.

Remove it and the bracket by unbolting, then 2, 10mm nuts that mount it to the exhaust manifold. It's kinda hard to get down there, but if you have a "wobble" extension it, helps. U-joints are too flexible for the angle unless you can get another finger down there to stablize it. You can disconnect the rubber hoses (if I recall), that go to it. I think I did.

Once that's off, it's pretty much the same process as the front.

[Bill's GXP]

Thanks. I was hoping that it wasn't a water line. BTW, I used Bosch Iridium plugs. I bought a new set of coils for the rear. Don't want to do this again if I don't have to.

[CMNTMXR57]

They'll be fine. The harder the metal, the longer they last.

[L82shark]

Been awhile since I posted, I had gotten so disgusted with this car I just wanted to forget I ever bought it. Only 33k miles on it now, pulled the plugs and took a compression check, kept getting varying readings from different cylinders, replaced the plugs and both coil packs and still having the miss on startup, 45 seconds later it would run fine, but then began gradually overheating, replaced thermostat and water pump,(figured it was gonna be the heads but had crossed fingers) flushed cooling system, only to have it run hot every other day when it felt like it. Due to the varying compression readings I finally bit the bullet and carried it to the only shop around that would work on the Northstar and had them to diagnosis it. Local GM dealer said it would take them two months to repair if it was the head gaskets, but they do give a 12 month 12 thousand mile warranty now when they do it. Then I found out GM dropped the motor and carried it to they guy I had fix mine to do the head work. They dropped the motor and pulled the heads after conducting their own tests and verified the headgaskets were leaking. Keep in mind this car had passed the sniffer test for the headgaskets and wasnt putting antifreeze out the tailpipes. $3600 later I now have a trouble free GXP that runs great. This has been a love hate relationship over the last few months, I love the rest of the car, I fit in it like it was made for me but that *dang* Northstar has got to go. I am shopping it around this week to trade for something with an LS or LT engine for my new daily driver.

If I could get an extended warranty on it I might keep it but I dont see the value of throwing more money at this thing when the other issues arise. Working up a swap for a 78 T/A with a 4 speed right now, hope I can pull it off. Pontiac screwed up with the Northstar, should have put an LS1 or something else in this otherwise great car.

[CMNTMXR57]

The LS4 wasn't yet available in 2004 and since the platform of the Bonneville is psuedo-shared with the STS of that generation, it was a cost thing for GM. Why reinvent the wheel when what you have works already. While we all rag on the N*, your issues seem to be an exception. Early N*'s had the head issues, by 2004, they had for the most part worked them out and for hte most part, the engine is/was fairly reliable. It'll leak oil, but still reliable. Other than being a size 10 engine in a size 5 dress, the N* is also a "modular" setup in that most parts are pretty easy to R&R also, which was a factor.

And FWIW, the LS4 isn't much easier to work on in a FWD platform. It is a size 8 engine in a size 5 dress, and those vehicles with LS4's (Impala SS's and Grand PRix GXP's) also come with weaker 4T65E transmissions. So pick your poison.

If you want an LSx motor, you need to get it in a GTO, G8, CTS-V, TBSS, current Camaro (or 4th gen Camaro/Trans Am if going back that far), or Corvette.