Hello, I just bought this 1999 mustang 3.8. for my daughter and have notice when letting off the throttle, there is little to no decceleration until the brakes are applied. Also, from a complete stop, letting off the brakes, the car accelerates without depressing the throttle to 15 mph by the end of a city block. Any ideas? Thanks Tony.

 

I assume its an automatic, right? Sounds like your the tranny clutch isn't disengaging when you press the brake pedal. Start with the basics. Check the tranny fluid and its level. It should be blood red. If it is black its dirty. If its brown its burnt up. Either way, the fluid and the tranny fluid filters should be flushed & replaced.

Is the Check Engine Light or any other indicator light on? If so, take it to your local auto parts store and have them read the codes for you (call ahead of course).

Good luck...

 

Thanks. yes it is a automatic, and I did have the tranny flushed already(about a month ago) But when you hit the brake the speed and rpm do go down it is just does not give you the feel of throttle decceleration when you let off the throttle pedal and thats when I notice when I release the brakes from a dead stop it will clime up speed and shift to about 15mph by the end of the block. Now ive ahave been told that my TPS might be bad and sending a bad signal to the computer.Thanks Tony.

 

After thinking about this more, I think what your experiencing is normal.

From your description, it sounds like you're expecting the car to slow down when you let off the gas like it does with a manual transmission (e.g. compression/engine braking). That doesn't happen with automatics. When you let off the gas the car effectively goes into neutral (simplest explanation). So it will coast for quite a while.

As for the car moving when you let off the brake after stopping, this too is normal with an automatic. Although 15 mph seems a bit high to me (could be due to a bad TPS). My girly's ride and my truck do the same thing, but only up to about 5-10 mph (doesn't even register on the speedometer).

What RPM range does it sit at idle? If your TPS or IAC valve was bad your idle would be high or fluctuate.

 

Well that's the thing the rpm at idle is about 7- 800rpm but it will clime up as the speed goes up . That's were the suggestion came about the TPS if its not working properly its send a different signal. I check volts to it and at first read it was .85 and did the adjustment and got it to about .94volts but it should be .98 to.99 volts but that's the highest I could it. so the thought might be a bad TPS. Thanks Tony. Sorry no check engine has come on at all either.

 

7-800 RPM's in drive? Or, in neutral.
In neutral, that would be good, in drive that would be too high.