Hanging rpms....still

[Tk469]

99 Gt. Bought the car from my son a few days ago. He "never noticed" that it increases rpm when you clutch/shift. Goes to 2k then very slowly drops. Replaced iac, cleaned maf, cleaned throttle body (professional products powerflow air inlet, bbk power plus TB 70mm) installed hose clamps on all the hoses from the k&n cold air. Replaced PVC grommet. Checked hoses up top for vacuum leaks. Disconnected battery. Still hangs. Any thoughts.

 

[wmburns]

What does the RPM's drop down to when the car is moving? What do the RPM's drop down to when the car is stopped?

Are you aware that Ford has designed the RPM's to be elevated when the car is moving. Usually 1100-1200 RPM's. This is done to allow the hydro-boost to function.

A factory car should fast idle (1100-1200) while the car is moving and drop down to slow idle once the car comes to a stop.

Do you really want to trouble shoot this? If so, knowing what the IAC duty cycle will answer the key question to give focus to trouble shooting. For that you will need an ODB2 scanner capable of accessing operational PID's. Having a data logging capability is a plus.

Here's some information on an affordable Windows based ODB2 scanner.


ForScan ODB2 scanner w ELM327 USB
https://www.stangnet.com/mustang-forums/resources/forscan-odb2-scanner-w-elm327-usb.57/

 

[Tk469]

What does the RPM's drop down to when the car is moving? What do the RPM's drop down to when the car is stopped?

Are you aware that Ford has designed the RPM's to be elevated when the car is moving. Usually 1100-1200 RPM's. This is done to allow the hydro-boost to function.

A factory car should fast idle (1100-1200) while the car is moving and drop down to slow idle once the car comes to a stop.

Do you really want to trouble shoot this? If so, knowing what the IAC duty cycle will answer the key question to give focus to trouble shooting. For that you will need an ODB2 scanner capable of accessing operational PID's. Having a data logging capability is a plus.

Here's some information on an affordable Windows based ODB2 scanner.


ForScan ODB2 scanner w ELM327 USB
https://www.stangnet.com/mustang-forums/resources/forscan-odb2-scanner-w-elm327-usb.57/

It's fine while moving, like you said around 1k. It's just when I shift yo. This is my first modern muscle car and my first manual other than the semi I drive at work. Maybe it's normal. Ex. When I am leaving a stop shift from 1 to 2 it hangs at 2k or so and hovers there before slowly coming down to that 1k range. It seems weird to me but I've gotten a little used to it. The idle screw is not even touching the stop and it idles at 900 warmed up. Miss the days of those old Holley Pumpers when I knew what I was doing. Lol

 

[wmburns]

IThe idle screw is not even touching the stop and it idles at 900 warmed up.

^^^This is a problem. The throttle MUST return to the SAME position every time the throttle is closed. If the throttle is not resting on the idle stop screw then the vacuum action of the motor will "pull" the butterfly closed more or less as engine vacuum changes. This will lead to an unstable TPS position which will cause the PCM to not have the correct TP-MODE value.

Here's some more information that may help.

Troubleshoot IAC idle problems 1996-2004
https://www.stangnet.com/mustang-forums/resources/troubleshoot-iac-idle-problems-1996-2004.13/

Pay attention to HOW the PCM uses the TPS position to affect TP-MODE. Also read about the virtual "ratch" function of the TPS. This is key to trouble shooting idle and IAC issues. Hanging 2000 RPM's between shifts is a little high. I suspect that the throttle is not closing all the way and TP-MODE is equal to part throttle (P/T). This could easily explain why the idle is so high.

Regarding ODB2 data logging. Over lay log the RPM's, TP-MODE, IAC, and MAF and I suspect the problem will jump right off the graph.

 

[Neuron]

I went through the same thing on my first "modern" stick shift and was convinced something was way wrong after driving an older one. Before the dashpots on the carb came into being the idle dropped instantly with that big return spring on the Thermoquad. With what you have done it might just be you getting used to it, except the 900RPM sounds a little high. The tachometers have been known to be less than accurate but usually in the upper RPM"s is where you see it most.
PS- You did get lucky and got wmburns to help, he is a wonder on the forums(even more so if the OP would take his advice lol).