So a few months ago my car began surging in stop and go traffic sometimes almost causing curb checks and fender benders. And my car slowly speeds up to 50 mph. I can put my car into drive and let go of both pedals and it will accelerate and shift by it self, going 20 to 30 in roughly 5 to 10 seconds. I have checked for vacuum leaks, changed the MAF and cleaned them, changed the IAC twice, changed the TPS the throttle cable and cruise control cable feel free with some play, I have also cleaned the throttle body out and used tons of fuel system cleaner. It just had a full tune up 6 months ago, except fuel filter which I am replacing due to some hesitation and hard starting. I have also noticed while coasting down the road if I tap my gas the RPM's actually drop slightly but pick up normally as I depress my accelerator pedal. My car is not equip with an EGR valve. I am very very stumped and I feel like I've tried everything in the book. Car idles fine between 7 to 9 hundred. Help Please!!
Hello. From what you describe, it would appear that you have already addressed many of the possible sources of the issue. A few other things I would check are the throttle position sensor and the fuel injectors.
The throttle position sensor is an electronic sensor that detects the position of the throttle plate. This is an important signal to engine calculations and can completely disrupt the engine management system if it gives a bad signal.
Another thing I would look into is the fuel injectors. Bad or leaky fuel injectors can sometimes produce the symptoms you are experiencing. If enough fuel is leaking from the one or more of the injectors, it may cause the vehicle to experience all sorts of issues.
A problem with either of these two components may cause the vehicle to experience hard starting and hesitation, as well as the distinct acceleration problem you are having. After that, I would then begin to look at other electrical components, such as the injector module, or even the main engine computer. If you need further help with this, a certified technician from YourMechanic can come to you to test the vehicle and determine what needs repair.