This problem just started about 2 days ago. I have a 89 mustang Gt and this is the first summer i've had it. Whenever i pull up to a stop sign or stop light, the motor revs to about 3000 rpms then drops almost to the point where it stalls out. On a few occasions, it actually does stall. The car accelaterates fines but occasionally it does not accelerate as fast as it should. Also if i'm at cruising speeds of say 45 mph and its kind of in the bottom rpm range of the current gear, sometimes the rear end seems like its slipping and even occasionaly seems like the fuel isn't quite combusting properly the all of a sudden ignites again. the motor was rebuilt about 7000 miles ago and the tranny has about 2000 miles on it and its an automatic. one more thing that when the motor is surging--if i shift to neutral or park it stil surges like that.

 

Try to clean you IAC "idle air control motor"and see if that helps.

 

appreciate the help--tomorrow morning i'm gonna replace the fuel filter to start and try your suggestion. This is kinda my project car and hate to see her run like this and since i'm taking my family on vacation next week, i don't have a bunch of money to spend right now.

 

It could also be a bad ECU.But try the cheaper stuff first and before you go spend big bucks,take it to a shop that can test OBDI systems and see what codes are pulled.

 

thanx again here's a pic of her

 

i think you can take it to auto zone or something and they will take codes off the car right....just in case so you can find out if there is any code for it

 

took it to autozone---they said they read the codes off of anything older than a '96. replaced the air by-pass valve and the fuel filter today and still have the same problem. gonna try cleaning the idle speed control motor next.

 

well turns out after working on the 5.0 for a couple hours, i took the air box completely off and low and behold i discovered this on the side of the therm pump






i don't know if its all of my issues but i'm sure it doesn't help any. now i just gotta try and find one of these bad boys.

 

woah.....u killed it lol

 

arrrrrrr---i just got back from napa, autozone, advance auto parts and the local dealership. no one carries this part. if anyone can help me i will gladly pay $$ for this part. HELPPPPPPPPPPP