1996 Chevy Lumina Vibration/Loss of Gas Mileage I can't fix

  • 6 CYL
  • FWD
  • 200,000 MILES
This will be a long background because I have done A LOT of replacing to fix this problem. When my car hit 200K, I did a lot of preventive maintenance/replacing of parts, as listed:

Ball joints
Outer Tie Rods
Front Control Arm Bushings
Front Shocks/Strut Bushing
Rear Struts/Mounts
Springs Insulators
Front Calipers/Rotors/Pads
All rubber brake hoses
Rear Wheel Cylinders
Rear Drum Springs
Rear Trailing Arms
Rear Lateral Link Bushings
All Wheel Bearings/Hubs
Both CV Axles
Upstream and Downstream O2 Sensors
Spark Plugs (originally had Bosch Plat, then changed to Autolite Double Plat after shop said they were lower quality, possibly causing misfires)
Spark Plug Wires (Xact)
Ignition Coils (All 3)
Engine/Transmission Mounts
Torque Strut Bushings
Transmission Fluid (Valvoline 75K+)
Oil Change (Fluid and Filter)
Fuel Filter
I have a K&N air filter that I just cleaned and recharged
Uniroyal Tires (30psi, just checked)

That should be everything. The vibration is noticeable when I'm at idle and when I get on the highway (50+). Can feel it in the steering wheel and in the floorpan. It feels like a high frequency "buzz". Also, I use to get 26-27mpg out of her until recently, now I get 22-23mpg. I think the two are related.

It's not tire balancing. I first bought Goodyear Viva 2 tires at Wal-Mart. I had them balanced 4 times with no fix. Even had two of them replaced because a Goodyear shop said they were bad. Still no help. Then had all 4 replaced with the Uniroyals. STILL THERE! Took to Goodyear shop to have balanced. Helped some, but still there.

I have not rechecked the misfires on a computer since I replaced the plugs, but I made sure they were.060 gap, as per Haynes, and the vibration didn't change.

The only code I'm getting is 0401: Insufficient Exhaust Gas Recirculation, which I've had long before this started happening.

So I'm completely lost as to where to go next. Could it be something internal to the drivetrain (bearing?)? Any help is GREATLY appreciated.
Do you
have the same problem?
Monday, July 13th, 2009 AT 5:30 PM

2 Replies

Have you checked to make sure there isn't a bad motor or transmission mount. The rubber sometimes goes bad and you can get a vibration from the steel to steel connection between the engine and frame.

Also, based on the code, have you checked the EGR to make sure it is working properly and there are no vacuum leaks?
Was this
Thursday, July 16th, 2009 AT 10:30 PM
Yep, already replaced both motor and transmission mounts (in list of replaced parts).

The code I have for the EGR valve has been there since I bought the car, and it has never had an impact on power or gas mileage (use to get 30 mpg on the highway). I haven't done a good check of the vacuum hoses though, so I'll take a look at those.

I did check my spark plug wires (also brand new) and their resistances are between 6.9K to 7.5K ohms, which is well within limits according to my Haynes manual. What's next in line for the spark? PCM?

Any other ideas?
Was this
Friday, July 17th, 2009 AT 7:25 PM

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