Vibration at idle - with A/C on.

Discussion in '80-Series Tech' started by Andrewsreef, Jul 16, 2005.

  1. Andrewsreef

    Andrewsreef

    Messages:
    191
    Likes Received:
    0
    Joined:
    Jul 22, 2004
    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
     
  2. IdahoDoug

    IdahoDoug

    Messages:
    8,864
    Likes Received:
    264
    Joined:
    Aug 9, 2003
    Andrew,

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

    DougM
     
  3. MLX450

    MLX450

    Messages:
    630
    Likes Received:
    9
    Joined:
    Apr 10, 2005
    Location:
    WA
    With the A/C compressor on the idle should adjust and rise to 800 to 1000 rpm.
     
  4. tarbe

    tarbe

    Messages:
    1,490
    Likes Received:
    37
    Joined:
    Aug 6, 2004
    Location:
    Houston, Texas for now - Romance, MO soon!
    Mine does the same thing, Andrew. So it is either normal, or we are both in trouble.
     
  5. Andrewsreef

    Andrewsreef

    Messages:
    191
    Likes Received:
    0
    Joined:
    Jul 22, 2004
    Thanks DougM and others.

    Andrew
     
  6. Boston Mangler

    Boston Mangler

    Messages:
    3,589
    Likes Received:
    5
    Joined:
    May 21, 2004
    Location:
    San Diego
    Ditto here too! Funny, i had a friend as me that 3 days ago.
     
  7. rgmax

    rgmax

    Messages:
    28
    Likes Received:
    0
    Joined:
    Aug 25, 2004
    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.
     
  8. ajohnson

    ajohnson

    Messages:
    23
    Likes Received:
    0
    Joined:
    May 31, 2005
    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.
     
  9. alaskacruiser

    alaskacruiser

    Messages:
    1,619
    Likes Received:
    21
    Joined:
    Mar 30, 2003
    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.
     
  10. ajohnson

    ajohnson

    Messages:
    23
    Likes Received:
    0
    Joined:
    May 31, 2005
    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'.
     
  11. Rookie2

    Rookie2

    Messages:
    3,036
    Likes Received:
    87
    Joined:
    Dec 15, 2003
    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.
     
  12. gbell210

    gbell210

    Messages:
    553
    Likes Received:
    3
    Joined:
    Jan 11, 2005
    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: Jul 21, 2005
  13. OZCAL

    OZCAL

    Messages:
    1,216
    Likes Received:
    3
    Joined:
    Nov 16, 2004
    Location:
    Queensland and California
    Ironically my idle vibration decreases when I turn the A/C on. Counter vibrations canceling each other out?
     
  14. LCconvert

    LCconvert

    Messages:
    98
    Likes Received:
    0
    Joined:
    Aug 18, 2005
    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!!
     
  15. elmariachi

    elmariachi

    Messages:
    1,977
    Likes Received:
    23
    Joined:
    Jan 4, 2005
    Location:
    Shufflin' Through the Texas Sand
    Its a plague, just like the headgasket.
     
  16. RAYJON

    RAYJON Get a bigger hammer..

    Messages:
    1,689
    Likes Received:
    206
    Joined:
    Oct 20, 2005
    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...
     
  17. concretejungle

    concretejungle SILVER Star

    Messages:
    9,558
    Likes Received:
    762
    Joined:
    Oct 27, 2003
    Location:
    North Cadillac
    i figure it's just the john deere effect.
     
  18. BROKEROB1

    BROKEROB1 SILVER Star

    Messages:
    562
    Likes Received:
    158
    Joined:
    Jul 19, 2004
    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 ;)
     
  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.