My 2006 3.6 liter V6 RWD STS AUTO TRANS (with Performance Package) has approx 60K miles. At about 50K miles, It started "lugging" about 3-5 seconds into a slight grade with cruise on or steady gas pedal. A slight manual acceleration will bring it back to smoothe running. The cruise control will allow the engine to continue to lug. If I do not give it more gas, the lugging will soon turn into engine shaking enough that it will cause the car to shake. I heard somewhere that, in order to gain better fuel economy, the factory specs on fuel mixture were too low. Is this condition normal and acceptable? Is it a serious problem that will do damage? Right now, there doesn't seem to be any damage. Is there a simple remedy for this condition? Has Cadillac issued a technical service bulletin on this problem? I will greatly appreciate some insight into this situation.

SOURCE: lug nut torque

96 ft/lbs

SOURCE: 1999 Cadillac STS

first u have to ask yourself what type of maintenance have u done via fuel filter ect,,get presure on rail check if it does not read right check regulator if you here an irreguler humm from your fuel pump will usually give you warnnin it is going out with change of this filter. I recomend!!!change the regulator with this repair.

SOURCE: rounded-off lug nuts

The auto parts stores cary a special kit for removing these wear eye protection and if you have air tools it will make it much easier. don't use sockets not rated for air tools (they break and will hurt you)

SOURCE: Why is my 1994 Chevy S10 Blazer lugging?

Could be vacuum leak or bad ignition wire(s).

I had a similar problem on my "93 Ford probe. The engine idled pretty rough with shakes, Turned out to be a head gasket leaking engine coolant into the cylinder during low rpm's. At fast rpm's it was fine becuase the internal cylinder pressure was greater than the hot coolant pressure & would prevent the coolant from leaking in.

A friend has the same problem with his "94 Blazer 4.3 L, throttle body injection, manual tranny. He hasn't fixed it yet, It started a few weeks ago & is getting worse. His gets a fast idle with hiccups which causes the engine shake. He already checked the EGR valve. He also has a severe exhaust problem, Not oilly but very gray & terrible smelly, but only when the fast idle problem happens. THis fast idle hiccup problem starts when the engine is warmed up.

SOURCE: lug pattern for 1999 Chevy Malibu

the lug pattern should be 5x100mm, you having the loaded malibu it could be the 5x125mm. if you still have the factory aluminum wheels on there then you can either take one off and look on the back of the wheel you will have to look closely it will tell you though, or you can go to www. tirerack.com there website will navigate you through and give you the proper size. hope this helps. sorry not more specific.