Help Me Diagnose a Rough Idle

[Charlie hermens]

Hey y’all, so I just finished throwing a new transmission and doing a clutch on my 05 lgt and I’ve noticed that after the cars been sitting for awhile it’s developed a really horrid idle, where should I start in diagnosing this, plugs? Injectors? Any help would be greatly appreciated I just want this thing running like new after all my recent work lol.

[Charlie hermens]

I also should add that there’s no roughness when I’m moving in gear that I’ve observed it’s just at idle.

[Pleides]

Spark plugs would be the place to start. I recommend doing them with the car jacked as high in the sky as you can get it. Much easier to do them from underneath.

[Infosecdad]

I would check for a disconnected or loose vacuum hose. Clamps or zipties help.

 

When you say "sitting a while" you mean the time that it took you to replace the transmission and clutch or it's idling for a while, then falls off the wagon and gets jumpy?

[Charlie hermens]

I’ll start there, I also went for a few laps around the block last night and I noticed I’m making like half of my peak boost aswell.

[apexi]

I've heard #7 / the blue T seems to be a common leak point

https://legacygt.com/forums/showthread.php/intake-vacuum-leaks-and-you-pics-inside-235626.html

[Charlie hermens]

I've heard #7 / the blue T seems to be a common leak point

https://legacygt.com/forums/showthread.php/intake-vacuum-leaks-and-you-pics-inside-235626.html

 

Sure enough, just got looking through everything and bingo there’s no hose connected to that blue T just like you said, thankyou all so much for the help I really appreciate it.

[JoeInOregon]

Just had this happen after I had my clutch and tranny swap done , would die out at idek , with throttle it it was fine

 

Took it back to the shop right away.

 

They used scan tool to do a throttle body re learn and it it fixed it.

 

They said I probably should do plugs as well but sometimes after pulling the battery it's need to do a relearn especially if you have a less ideal idle to begin with that the ECU has learned to deal with

 

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[Charlie hermens]

New development lol, so I did what JoeInOregon said which worked, kinda, my accessory isn’t showing any cylinder roughness, but it threw a code, which is PO171 Fuel system lean (bank 1), I’m at a loss here, any advice would be greatly appreciated.

[Pleides]

Could be a bad cat, a bad O2 sensor, or a vacuum leak. All three would give you rough idle but a bad cat you would probably hear. Anybody been out stealing catalytic converters in your neighborhood?

 

O2 sensors seem to go bad on our cars with some regularity. Our cars are also ok’d and have a decent chance of developing vacuum leaks because of the age of seals and rubber.