Vibration at idle - with A/C on.

Joined
Jul 22, 2004
Messages
191
I had a friend in the truck the other day and he asked why the truck was vibrating so bad at idle. It goes away when the A/C is not on. I guess I did not notice the gradual change. Is this a sign of the compressor going bad?

While changing the oil today, I listed to the truck at idle with the hood up. With the A/C off, I beleive I am hearing some noise from one of the pulleys. Could just be some valve train noise as I can't tell for sure where it is coming from. With the A/C on, I can't hear it at all and it appears to be smooth (not in drive so not same exact situation). How do you isolate what pully/tensioner is bad if any? I had the belts replaced a while back but I did not replace the tensoner.

Thanks

Andrew
 

IdahoDoug

 
 
Joined
Aug 9, 2003
Messages
8,868
Andrew,

Get a mechanic's stethescope, or use a wooden dowel to listen to each pully or tensioner.

DougM
 

MLX450

 
Joined
Apr 10, 2005
Messages
630
Location
WA
With the A/C compressor on the idle should adjust and rise to 800 to 1000 rpm.
 
Joined
Aug 25, 2004
Messages
28
Location
Orange County, Ca.
My 96 LC also vibrates with the AC on. I took it to the dealer but they were unable to correct it. It does not seem to me that this should be normal. A couple of questions...

1) Does anyone have a smooth idle with AC on?

2) Of those who don't have vibration how much does the idle increase when the AC cycles on?

3) Those with vibration, how much idle increase? Mine idles 750-800 rpm with AC on.
 
Joined
May 31, 2005
Messages
23
Location
Chandler, AZ
Same issue here on my 'new' '94. Had also wondered if something was wrong, especailly after just driving 1500 miles in 25 hrs from Phx AZ to Memphis TN.

That was my time including several stops for walkign around a bit. Had the wife to share driving tasks. I checked mileage on every fill, had roughly 15.5 mpg on every tank.
 
Joined
Mar 30, 2003
Messages
1,619
Location
LA, CA
Same behavior on my '97 LX since I got it at 35k mi. Same thing on my old '93 80, as well. I think it is normal.
 
Joined
May 31, 2005
Messages
23
Location
Chandler, AZ
Noticed driving around yesterday that mine doesn't always run rough at idle with the AC on, but it does most of the time. When it doesn run rough at idle (like at a light), the roughness seems to increase a bit before holding steady. It does seem to be pretty rough at this point, so I don't think one could call it 'normal'.
 

Rookie2

 
 
Joined
Dec 15, 2003
Messages
3,044
Location
Knoxville
I've never noticed it on mine. Obviously there's an rpm change when the AC kicks in, but on these large displacement motors, I feel like the motor is smoother with less vibration at the higher RPM's.
 
Joined
Jan 11, 2005
Messages
554
Location
Poulsbo, WA
I've noticed on my 94 that when I turn ON the AC rpms rise to around 900 and idle is smooth... but when I turn the AC OFF the idle drops down to 400, sometimes staying there and idling rough while other times slowly rising back to 600 (normal idle). This 400 rpm idle is not always after I have shut off the AC sometimes its in the morning after the truck has just warmed up, but other times it is fine with a 600rpm idle.

I have not checked the black rubber intake yet for cracks, but I will do that. Also, I know I have an exhaust leak somewhere around the cats (before them I think). Would either of these cause this intermitant rough idle?
When idling at 400, if I apply gas to get it to 600rpms it idles just fine.
Any other ideas on where I could look? When I first bought the truck 6 months (end of January) ago it did not have this problem, but has seemed to slowly develop it.
Thanks for any help,
Gary
 
Last edited:
Joined
Aug 18, 2005
Messages
98
Did anyone ever find out what was the possible cause of this? My idle gets pretty rough with the ac on. The idle does rise as expected and stay steady but the truck shakes noticably more.

I know this seems early in the year for ac questions but here in AZ we start early!!
 

RAYJON

Get a bigger hammer..
 
Joined
Oct 20, 2005
Messages
1,721
Location
Reno NV
Try cleaning the throttle body and the idle air control valve.. really helped my 93 but the 97 does it no matter what I do...
 

BROKEROB1

SILVER Star
 
Joined
Jul 19, 2004
Messages
596
Location
York, PA
I had not noticed mine, until a HARD day of wheeling. The vibration started when I kicked the AC on for the trip home. It was so strong that it hurt my ears at certain frequencies. When I got home, I checked the underside of my truck, particularly the exhasut. I had broken just about every one on my mounts. The exhaust was touching the frame in several places. I still have not properly welded the exhaust back yet. I did "wire it up" with some pretty thick guage coat hangers:grinpimp:
That has helped some, but I still have some vibration when the AC is kicked on. Not sure if that is your culprit, as I think it could be so MANY different issues. But thought I would mention it b/c it was my experience. So maybe, check your mounts ;)
 
Top Bottom