odd vibration at idle

[natedogg11c]

my 97 is my daily so I've gotten used to all the shimmy's and shakes it has, but the other day it seemed to vibrate the cabin more than usual at an idle. when I'm driving along everything feels smooth and normal but when i would come to a stop and the motor would idle down to 600 rpm it would send a noticeable vibration through the truck. if i idle it up even to 700 rpm it would go away. its had new plugs and wires over the summer and I'm planning on doing the timing belt and valve cover jobs at some point over this winter. truck has 290K miles on it could it be wore out motor mounts?

 

[spartacus]

Had similiar symptoms.The dampner on the drive train under the truck was loose. But it could be other things. check the drive shaft joints for play and grease them.

 

[19963.4lsr5]

600rpm is normal in gear with brake on idle rpm.

Try running some good injector cleaner for a few tanks. Techron or Gumout or....


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[Dieselchessy]

Clean your throttle body and Idle Air Controll circuit (bottom of throttle body).
That and the MAF sensor.

 

[natedogg11c]

I wouldnt think the drive shaft would have anything to do with it. i may have forgotten to mention its only when im stopped. ill run some cleaner through the tank a few times and see how it works

 

[spartacus]

I wouldnt think the drive shaft would have anything to do with it. i may have forgotten to mention its only when im stopped. ill run some cleaner through the tank a few times and see how it works

If you dont have vibrations while driving then drive shafts shouldn't be an issue.

 

[mtbtim]

Definitely sounds like a rough idle and not a problem with the motor mounts. But, you could check the motor mounts by raising the hood, putting your foot on the service brake, parking brake on as a back up and then put it in drive. You'll be able to see the engine by looking through the bottom part of the windshield. Give it a little throttle and you should see the engine twist a bit from the torque but not actually lift up dramatically. If it does, the motor mount is broken on one side. Do the same in reverse and you'll see the engine torque the opposite direction and you'll be testing the other motor mount.

Since you've already replaced the plugs and wires, I agree what others have said and maybe a fuel injector cleaner in the gas tank along with a good cleaning of the throttle body and the IAC valve will improve your idle. Also check other basic things like your air cleaner. If it's really dirty, replace it. A dirty MAF sensor will usually throw a too lean CEL but it wouldn't hurt to clean that either.

 

[plcfcng]

With a rough high idle I would first look to see if you have a Vaccum leak:clap2:

 

[mtbtim]

With a rough high idle I would first look to see if you have a Vaccum leak:clap2:

But don't vacuum leaks usually cause a high idle? That's what I understood.

Update: Just did a quick search and lo and behold a vacuum leak can cause a slow idle, rough idle and high idle. It's just been my experience on this forum that people with a high idle problem often found a vacuum leak as the cause.

 

[19963.4lsr5]

But don't vacuum leaks usually cause a high idle? That's what I understood.

Update: Just did a quick search and lo and behold a vacuum leak can cause a slow idle, rough idle and high idle. It's just been my experience on this forum that people with a high idle problem often found a vacuum leak as the cause.

I had a normal idle rpm and the code for too lean after I fired up the fresh engine. I had the throttle body gasket on wrong. It was enough to cause a lean condition (from having combustion air bypassing the MAF sensor) but not enough to raise the idle.


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[plcfcng]

As I said earlier I would first look for a vacuum leak. After confirming there are no vacuum leaks from what you have said about plugs and wire being replaced already I would do the following. As you may have a compression issue a plug inspection can tell alot.

1. Get a engine compression tester (purchase or rent)

2. With a cold or engine that is cold enough to work on comfortably Pull each plug and look at them the should look very similar they should not look oily, fuel wet, coolant wet or other conditions better to google for examples.

3. Now to do a compression test
a. remove fuel pump relay have a friend crank the engine until you signal
them to stop usually 7 rotations you stop when the needle stops moving
up. You will see the pattern. Do each cylinder the same rotations record
each reading. with the Throttle plates open I do this by placing a Screw
driver handle in the throttle plates carefully. Or use a remote starter
switch then don't pull the fuel relay.

4. If a reading is about 10% from highest to the lowest your fine outside of
the u need more diagnosis.

5. If the readings are outside of 10% and below about 120 psi you can do a
wet compression test by squirting 1 or 2 squirts from a little oil can of
motor oil or atf and redo the compression test.



4. A lot of people do another test called a leak down test I find this is usual just extra work as this tells you enough. Good Luck :hunter:

 

[brillo_76]

If everything is looking good engine wise and vacuum wise.

Make sure your exhaust insulators are good and the exhaust isnt touching anything. I am having this issue on good old Tetanus 1. I had the muffler pipe bumping a crossmember. So until I get some new parts. I wired the cat flange up so it would not touch that crossmember. So now the sounds changed.

Even a loose exhaust heat deflector can rattle at idle. So can your cat cover shields too.

May not be the case in your particular issue but it's something that can be ruled out and all it will cost you is a little bit of time.

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[BoomerBob]

Worn torque converter might give it vibration at idle and in gear. If it goes away when shifted into neutral; just shift it into neutral at long stop lights.