I have a 1998 Monte Carlo with 196,000 miles. The car has been maintained well. However, it has begun to idle very high when in neutral (from 1500 to 3500 RPM's). When it's put into gear with the high idle, the car lunges and will accelerate to 45 mph without you ever touching the gas. From a stop, it doesn't seem that the transmission is shifting back to 1st gear as you have to step on it bring it to about 2500 RPM's and it doesn't accelerate quickly at all until it shifts down. Any ideas? The last time I took it to the dealership they told me my AC was going out (quoted over $1000 to replace) and my AC is still operating fine 6 months later. Therefore, I tend not to trust them at this time. Any advice is much appreciated. I have the 3.1 engine. I have only added a remote start system and alarm.

My '99 Monte also just started idling quite high. After startup, and before ever touching the accelerator, the engine will rev on its own to anywhere from 1500 to 3000 rpm. It lunges like mad after releasing the brakes at a stop sign. Engine will also rev up when I put the car back in park. This problem just started after I had the alternator replaced (w/ a refurb).

ChevyD : Since I made this post, I have found the resolution for every one of the complaints that I listed. I replaced both of my O2 sensors and have not had a single problem since. The front O2 sensor was easy, but the rear O2 sensor was a pain to get to (but it is possible). Good Luck and hope this helps you out. It was less than $200 for both of the O2 sensors (ofcourse that is with me doing the labor).