Slightly rough idle only in gear

[Schattenjager]

1997 Lx450 with 144k miles.

Idle is very smooth in park. Once a gear is selected, it is less smooth. Full throttle acceleration shows a low frequency whistle but I cannot find a vacuum leak. Runs fine, plenty of power, no exhaust smoke and mpg appears normal.

Just wondering if there is a common issue here. Did a vacuum check a la starter fluid. Two tanks of good gas and cleaned the MAS. Mobil 1 oil and filter change. Plug wires look to be fine and newish.

Ideas?

 

[40tude]

Check the intake hose. They can crack especially the bottom side. This would also make a whistle. Run a bottle of techron through also.

 

[Klierslc]

Whistle is likely due to the factory resonator. It is a common 80 thing...

 

[nely]

The less smooth feeling in gear is likely motor mounts. Not that they are broken just colapsed and causing vibration.

Sent from my SGH-T959 using Tapatalk

 

[Moody]

The less smooth feeling in gear is likely motor mounts. Not that they are broken just colapsed and causing vibration.

Sent from my SGH-T959 using Tapatalk

I just experienced a similar situation on my LX at 187k, it was the motor mounts.

I get a whine, but that is due to the resonator not being present on my truck.

 

[Rallyroo]

Idle is very smooth in park. Once a gear is selected, it is less smooth. Full throttle acceleration shows a low frequency whistle but I cannot find a vacuum leak. Runs fine, plenty of power, no exhaust smoke and mpg appears normal.

Check the intake hose. They can crack especially the bottom side. This would also make a whistle.

^This.

On my rig, it started out with a small crack in the bottom side of the intake hose (unknown to me). When I went into reverse the rig would shake as if it was about to stall. The movement of the motor during the gear shift caused enough movement the crack would open up on the intake hose; shifting back to park or drive the crack would close up. Eventually the crack got so big that the motor would constantly stall in any gear except for park or if I kept the revs up.

I was out on the trails and didn't know what was the source of the problem. Fortunately I was able to limp back home.

Next day I worked on the rig I discovered it was the intake hose. I replaced it and the problem went away.

Oh, in my case, it sounded more like a turbo sucking in air. My petrol engine was emulating a turbo diesel intake.

 

[Schattenjager]

If it is the intake boot - why would it be smooth out of gear? I think I am being hyper sensitive. The motor mounts are new and it runs great. Think I'll worry about something else, like:

Would a Snorkel get rid of the whistle - provided it is indeed the resonator?
:sombrero:

 

[Schattenjager]

Hose clamps / PCV etc

Just wanted to wrap up this thread, at least as far as my issue was concerned:

Replaced the PCV and grommet and put on a new hose. Problem was nearly rectified - adding hose clamps to the top of the PCV and throttle connection made a huge difference. There are several larger vacuum lines with out clamps, so I purchased a pack at Lowes and will replace the old lines with fresh and add a clamp, however unnecessary, to each connection.

 

[Schattenjager]

One last bit - I was very pleased how smooth the rig became after I replaced a couple of the exhaust hangers - primarily the one just above the rear part of the muffler. Could not tell the rubber was cracked through by looking alone. Apparently the exhaust had enough room and freedom to move that it was passing vibes into the body. After doing the belts, the vacuum lines and PCV and now this, the Cruiser runs like factory new.

 

[ScottyDog]

Thanks for the tips Schattenjager... My trucks doing something similiar. It feels like mildly rough idle when stopped at the light. Not enough to make the tack needle bounce around but enough that my hyper-sensitive, spider senses tells me its not right...

 

[Wheelingnoob]

Mine does the same 155k miles, replaced every tun up parts, intake manifold chemically cleaned when HG was being replaced. It has had a slightly rough idle since I got it before all the tune up work. I have started getting a PO136 (rear O2 sensor) code from time to time but its not effected the millage or the idle roughness. I plan to get a new one once the funds are available.

My next step is the MAF cleaner, I'll give that a shot.

Over on MUD its a common problem with the 96-97's as far as I can see.