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Chasing a vibration

 
Old 03-15-19, 05:28 AM
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TrueGS300
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Default Chasing a vibration

I am having a slightly annoying vibration at idle. Mostly stopped in drive with a/c on (as loaded as possible). I have gone after if from both engine performance and mounts. The car was idling low and had occasional no-starts and rough idling. I did a full intake removal to replace my knock sensors. At this time I did plugs, coils, PCV valve, deep clean of the throttle and intake plenum, and IAC valve. The car runs way better and almost perfectly smooth, but not quite as smooth as I had hoped. Picked up a lot of power too.

I have replaced all three engine mounts, which I didn't notice much of a difference from. But did not do the transmission mount as it looks good and solid, nor did I do the shock looking thing in front of the radiator. I was wondering about that shock looking thing. It never even comes up when I search for mounts. What does it have to do with the engines stability? It hooks from engine to sub-frame. Could it or a weak trans mount be the cause?

I also ran into something not covered in the IAC DIY's when cleaning mine that could have to do with it. When you remove the electrical portion and can move the flap, no one says where the flap needs to sit when re-installing the actuator. It seems to put it where it wants, but maybe it's not perfectly lined up? This vibration really is "slight". Any car this age is expected to have some imperfections, but I feel I have mechanically restored too much for it not to be near perfect at this time. As a tech maybe I am being to sensitive to it.

Im leaning toward the IAC still being the culprit. The PCM should make up for loads by raising the rpm accordingly when say a/c is on. It does drop the idle lower when a/c is on and the vibration can be felt. I think the IAC is what is used to make up for this.
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Old 03-15-19, 06:31 AM
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JohanH
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These cars are way less refined than the GS300, being V6 they are inherently instable.
Coming from a GS300 myself I found the vibrations annoying at first as well.
My engine mounts seem ok, so I tend to look at the vibrations as a feature, not a defect....

I would get rid of them if there was a cure, but judging from the threads on this forum, it's a hit and miss.

Not helping your problem, just adding my 2 cents.

Cheers
Johan
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Old 03-16-19, 07:26 AM
  #3  
salimshah
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Originally Posted by TrueGS300 View Post
I am having a slightly annoying vibration at idle. Mostly stopped in drive with a/c on (as loaded as possible). I have gone after if from both engine performance and mounts. The car was idling low and had occasional no-starts and rough idling. I did a full intake removal to replace my knock sensors. At this time I did plugs, coils, PCV valve, deep clean of the throttle and intake plenum, and IAC valve. The car runs way better and almost perfectly smooth, but not quite as smooth as I had hoped. Picked up a lot of power too.

I have replaced all three engine mounts, which I didn't notice much of a difference from. But did not do the transmission mount as it looks good and solid, nor did I do the shock looking thing in front of the radiator. I was wondering about that shock looking thing. It never even comes up when I search for mounts. What does it have to do with the engines stability? It hooks from engine to sub-frame. Could it or a weak trans mount be the cause?

I also ran into something not covered in the IAC DIY's when cleaning mine that could have to do with it. When you remove the electrical portion and can move the flap, no one says where the flap needs to sit when re-installing the actuator. It seems to put it where it wants, but maybe it's not perfectly lined up? This vibration really is "slight". Any car this age is expected to have some imperfections, but I feel I have mechanically restored too much for it not to be near perfect at this time. As a tech maybe I am being to sensitive to it.

Im leaning toward the IAC still being the culprit. The PCM should make up for loads by raising the rpm accordingly when say a/c is on. It does drop the idle lower when a/c is on and the vibration can be felt. I think the IAC is what is used to make up for this.
Lets start by establishing if the idle rpm is correct or not before we look at other possible causes.
The slug in the IACV is the computer->magnetic-coil -> electro-megnatic field affecting the position of the slug -> opens up air channel is all part of the electronically controlled idle. You should assemble that based on the spin zone of the slug and then let the computer control it.

Once the passages are clean and the slug can twist freely under electromagnetic field, you let the vehicle learn/adjust. A few days of driving.

Please list the cold idle rpm.
Hot idle rpm with no load.
Hot idle rpm with A/C on.
Hot idle rpm with A/C on, lights on, brake applied [note the idle adjust as load is increased]

Salim

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Old 03-16-19, 06:42 PM
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I think the idle has learned and got better on it's own. It took a good week. Maybe mounts settling in and computer learning combined. Its gotten smooth now. Thanks guys
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