coasting idle it high

[sleeper95]

alright that problem is that i installed a new performance fuel pump that is 255 lph but now when it idles at 900 rpms it dies. so i adjusted the idle to be at 1100 so it wont die but now when im coasting it sits at 2000 rpms is that ok?

need help bad!

 

[sleeper95]

also another problem is that it takes a long time to idle down to normal when i stop

 

[HISSIN50]

How are you adjusting the idle? If using the idle-bleed screw, that can cause a hanging idle if it's run out too far.

I'd try to find the reason why it craps out when set to 900 RPM. That's well over the commanded idle.

Any codes?

 

[sleeper95]

there is no codes.
it started happening when i put in the new fuel pump.
im just trying to figure out why it takes so long to idle down

 

[HISSIN50]

How long ago did you run codes? You should not be passing with things set as they are and doing what it's doing.

 

[stangbangerrick]

Tell us about your engine set up, why the 255lph pump?

 

[sleeper95]

well what i have done to the mustang so far was edelblock intake, h pipe, 377 gear ratio, lsd differential, lighten pulleys and shifter kit.

 

[toyman]

alright that problem is that i installed a new performance fuel pump that is 255 lph but now when it idles at 900 rpms it dies. so i adjusted the idle to be at 1100 so it wont die but now when im coasting it sits at 2000 rpms is that ok?

need help bad!

Am I correct to assume that use adjusted the idle stop screw on the throttle linkage? If you did that will explain why it idles high when coasting. That screw is preset to prevent the throttle blade from sticking in the TB bore. By adjusting that screw you change the position of the TPS and the voltage output the computer uses to determine where idle closed throttle is. Idle is a computer setting based on a number of parameters. If you have adjusted the screw to the point where idle voltages are outside the computers acceptable range the computer can no longer determine where idle is. This is why you need to check for codes again. I would suspect that the idle issue first experienced is related to the TPS or IAC. Changing the fuel pump shouldn't have had any affect unless the FP regulator took a dump at the same time and is allowing the fuel pressure to greatly exceed the expected value of about 40 psi. So you might want to check fuel pressure as well.