RPM variation @ highway speeds

[pmh013]

I have an AWD with 20500km on it. I drive 210 km/day on the highway (105-115 kph). In the last couple of days, I have noticed this bizarre RPM variation:1. Set cruise at 110 kph (RPM = 2800)2. speed will drop to about 107 kph, car downshifts, RPM = 3000, still can't maintain 110 kph, car downshifts again, RPM = 4000. speed will go up to about 113 kph, car upshifts, RPM = 3000, then drops to 2800.3. repeat 1-3anyone seen this ... is the dealership going to assume i'm smoking something?

[Flip-Side]

If it has just started doing this, you should really go straight to the dealer to fix it. A problem like this could mean something is either in need of adjustment, or serious maintanance. Check all the obvious stuff, like oil and tranny fluid, running temp, or water in the fuel (colder regions). I really don't know much of the AWD system, but it is just one more thing that can break...so you may want to have it checked out. Hopefully its just a hiccup, but it's good to play it safe.

[vibb]

quote:I have an AWD with 20500km on it. I drive 210 km/day on the highway (105-115 kph). In the last couple of days, I have noticed this bizarre RPM variation:- If you set cruise to 107 kph, will the downshifting still occur?- If you turn the cruise control off and use the gas pedal instead to maintain speed, can you maintain 110 kph without the transmission downshifting?- If the answer to both questions is no, and your top speed is not only 115 Km/h (72 miles per hour), you may have set the cruise speed too close to a programmed shift point. This condition is call gear-hunting, and was once common in older cars, especially those with low torque engines.

[pmh013]

Just got back from the dealership this morning... The car was still acting up, until I was about 45 minutes away from the dealer, then everything was fine.To answer the previous question, I have been able to set the cruise to any speed and never had a problem maintaining it. This same phenomenon also happens without cruise, but because you are always compensating, it is less noticable.In any case, the dealer checked everything out. There were no codes that the car came back with, so they phoned Pontiac. They have had reports of Vibes with the manual transmission doing this, but not the automatics. I was told that if it does it again, phone back, and they will order in a computer module to replace (this is how they fix the manual transmission).TAFN