Why is my idle rough (1 Viewer)

[Brick]

Hey guys, my idle has been a little rough in my fj80.

In park my idle is normal and good at around 650 rpm. When I idle in drive (like at a stop light), however, my idle drops below 600 rpm and sounds really rough. My oil pressure gauge also drops but I figured that was just a normal thing for low rpm. Here is a video of the idle

Is this a normal feature of an 80 series? Or is there something I need to look into fixing?

 

[proteolytic]

Not normal. Possibly un-metered air via a vacuum leak. Check/replace all vacuum hoses. What year is your 80?

 

[Brick]

1991. I’m currently missing one of the hoses that is a part of the smog pump/air injection system— would that cause this?
*see picture for what hose*

 

[proteolytic]

I don't think it should as my smog pump was removed when I got mine. Not sure how that overall affects the engine. Is the part where it connects to the air injector tube (metal part in upper left part of the picture) capped off or open to the air?
A common culprit for air leaks is the large rubber intake hose connected to your throttle body (along with any of the other rubber tubing past your air flow meter).

 

[Brick]

Both places the hose was connected to are open to air

 

[UsedLuxury]

Check the torque on your intake runners. I had to tighten all of mine down. Your valve cover gasket can also be a leak. I replaced mine and that helped a lot.

 

[jonheld]

Any unmetered air entering the system will cause a rough idle. However you stated that it only happens in with torque applied, like sitting at a stop light while in DRIVE. This would point to a tear in the intake plenum that flexes when the motor shifts on the mounts.

 

[Brick]

Ok. I’ll have to check all of that when I get the chance

 

[Brick]

I just went and looked at the car— I don’t see any obvious problems with leakage. Is there anyway to diagnose some of the stuff you guys were talking about? Or do I just to do it and hope it solves the issue?

 

[Tedward]

It may not be obvious.
I think what Jonheld is getting at is a possible tear in the rubber intake tube pipe black bellows thing.
Goes from the air cleaner on the inner fender (body) to the throttle body on the motor (motor mounts/frame)
When your motor flexes and rotates a bit under load, the intake tube flexes at a possible crack/tear that may be allowing extra air in.
When it's all in the resting position the tear may be sealed up.
You could remove the intake tube and really look for any crack/tear with a light and flexing it a bit like it does in real life.
I'd start there. It's pretty low hanging fruit.
Can be temp fixed with tape or whatnot if you do find a tear.

 

[Brick]

Ok. I’ll make sure to check really well next. It looks great from the visible parts when it’s on, but I’ll take it off and check

 

[Hornd]

It may not be obvious.
I think what Jonheld is getting at is a possible tear in the rubber intake tube pipe black bellows thing.
Goes from the air cleaner on the inner fender (body) to the throttle body on the motor (motor mounts/frame)
When your motor flexes and rotates a bit under load, the intake tube flexes at a possible crack/tear that may be allowing extra air in.
When it's all in the resting position the tear may be sealed up.
You could remove the intake tube and really look for any crack/tear with a light and flexing it a bit like it does in real life.
I'd start there. It's pretty low hanging fruit.
Can be temp fixed with tape or whatnot if you do find a tear.

Take it off. Put One end on Table and Blow in Other End. You will find Leak if there is one.
Purists are gonna Flip, but have heard Good things about the Ebay Hose (~$40)
It serves a Simple Purpose.
Last I saw OEM was over $100.