My malibu has 210k miles on it. I've noticed that when an internal fan (don't know which one) kicks on under the hood, my temp gauge drops from operating temp (200) to flatline (100). When it does this, my RPMs jump up from around 500 to b/w 1100 and 1500. The car will surge forward, and if I'm at a light/stop sign/whatever, I have to press very hard on the brake to keep from moving forward. If I go to accelerate during the surge, my transmission shifts hard going into 2nd gear, and if I'm backing up during the surge, the transmission "yanks" for lack of a better word as I shift into drive. I do alot of interstate driving and even at a constant speed I notice the temp gauge floating up and down and the car surges then as well. It didn't have this problem when we bought it in February, but now that the summer temps are here, it does it constantly. We read on another forum last night that it may be the throttle position sensor, so we changed it about an hour ago, and we are still having the same problems. The check engine light is on too. Sry for such a long-winded thread..help me please!

 

Did you have the code pulled for the check engine light?

 

I did have the code pulled. P0118...to I replaced the ECT sensor and it seems to have solved the problems. I've driven my 100 mile work commute for the last 2 days and have had no problems at all, but of course i always keep my fingers crossed!