Random misfire

Hello,

Can you please pull the Direct Trouble Code[s] for us? Here is a link below explaining the process using a code reader:

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Please get back to us with the DTC[s] and we can go from there. Happy Holidays.

Thanks,
Alex
2CarPros

P0300.

Hello again,

Okay, so this could be a problem with an intake or vacuum leak. Here is a link below explaining how to test and track down a vacuum leak. Please pay special attention to the intake manifold section.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Please go through this guide and get back to us with what you find out. Happy Holidays.

Thanks,
Alex
2CarPros

Tried spraying around the brake vacuum and it made the idle a lot worse.

Hello again,

Okay, so there is probably going to be your vacuum leak. Please inspect the vacuum line going to the brake booster and get back to us with what you find.

Thanks,
Alex
2CarPros

Sure will and thank you!

I'm changing the vacuum hose Tuesday.
Do I need a new elbow and washer on the booster? If this doesn't solve the problem, what would be next? Thanks

I have new headgaskets and bolts and all new gaskets on the lower intake and plenum gasket and I rings on injectors also.

Hello again,

If the problem still persists I would move on to the ignition system next. New spark plugs is what I would recommend first. In the diagrams down below I have included the Original Equipment Manufacturer[OEM] part number for your reference and the recommended gap for you as well. Please keep us informed as to the results, and we can go from there, if needed.

Thanks,
Alex
2CarPros

Can't thank you enough, I put a new power brake booster vacuum hose and immediately saw and felt the difference. No more rough idle! I was ready to buy a new throttle body. You saved me a lot of time and money. The check engine light is still on, do I need to unhook the battery for a bit to clear it?

Hello again,

That is one method, but not the preferred one. It will work but the problem with unhooking your batteries negative battery cable for 5 minutes is that not only will it clear the DTC, it will also wipe clean the entire Keep Alive Memory[KAM] where your vehicle's PCM keeps all the learned adaptive memory and fine adjustments learned to make the engine run smoothly. The PCM will relearn these values, but it might run a little rough and have a few hiccups until then. The preferred method is to clear the DTC using a code reader. This will keep your PCM's KAM intact. Please let us know how it turns out. Have a Happy New Year.

Thanks,
Alex
2CarPros

I replaced the booster line but I can't find a replacement part for where it connects to the intake manifold? I have a PCV valve on the left side of motor (standing in front of car) and a fitting on the back of the upper intake and it's a little loose, and I want to replace it but no one knows what this part is? 2005 GM Buick 3800 series 3 3.8l engine(non turbo).help!

Hello again,

Okay, if it's a tube coming from the exhaust manifold then it is the Exhaust Gas Re-circulation[EGR]. If it's a hose it could be Idle Air Control[IAC], Evaporative Emission[EVAP], or Positive Crankcase Ventilation[PCV]. It could also be a coolant line going either into or out of the heater core. Where does whatever that attaches to it go to?

Thanks,
Alex
2CarPros

Sorry to keep bothering you.

Hello again,

You are not bothering me, this is what I do. Where does the other end of the hose go?

Thanks,
Alex
2CarPros

This the the upper intake. Picture is upside down. You can see the edge of new plenum gasket (black line). I just put some permatex high temp around the outside edge and a new o-ring on the black plastic piece.This should make a good deal.

Hello again, I see the upper plenum, what I am asking, my friend, is where does the other end of the hose go to, or come out of, depending on how you look at it. So not the end the goes into the upper plenum, but follow the hose and let me know where the hose leads to, please.

Thanks,
Alex
2CarPros

My mistake, it goes into the upper plenum. I was calling it the upper intake. The vacuum hose is coming from the brake booster down to this hole into the upper plenum. (My mistake. I'm a back yard mechanic)

Hello again,

I'm sorry too. I thought you were another customer. This looks like it will seal fine. You did a good job it looks like with the permatex. Very nice bead. Happy New Year.

Thanks,
Alex
2CarPros

Thank you for all of your help! Saved me a lot of money. I will have to let others know about this. Can't believe this doesn't cost anything like other sites. Amazing

SCGRANTURISMO is one of our best! Use 2CarPros anytime, we are here to help. Please tell a friend.

I changed the brake booster Vacuum line, drove it for a hundred miles and it's back to a rough idle at stop light?

Have you tried servicing the throttle bore? this guide will help:

https://www.2carpros.com/articles/throttle-actuator-service

Please run down this guide and report back.