Strange RPM Problem

[BLKsteeda]

Ok, I'm completely stumped. I have an 01 GT and I'm having a strange RPM problem. First off, I have full bolt ons plus ported heads and cams and a custom dyno tune and I've been working very closely with the tuner to try and figure this out. He believes it may be with the Throttle Body (Accufab) Here is what is going on:

When I press the clutch in and let the car coast when I want to come to a stop, the rpms will get stuck at 2k and will not drop till the car comes to a COMPLETE stop. When the car does stop it takes about 10 seconds for the rpms to return to idle...its not a smooth drop either, it does it in steps. If I'm completely stopped and inch the car forward slightly, something is telling the car that it's moving and the rpms go straight up to 2k and waits till I come to a stop and does the 10 second drop thing again. If I'm driving the car with the rpms below 2k then press the clutch in to coast, the rpms will still shoot up to 2k until I stop completely. Now, it was recommended that I back off the Throttle Stop Screw a little bit more, I did that and now with the AIR ON, it runs perfectly, the rpms drop to about 1200 when I coast and drop to 900rpm when I stop...with the AIR OFF, the problem is still there!!!

Here is what I have done maintenance wise so far:

new air filter
my MAF is a new stock replacement as my last one went bad with low voltage
cleaned my TB/Plenum with seafoam spray cleaner
my IAC is new (4 months old) removed and cleaned it anyways
PCV Valve is new
removed my EGR and cleaned it
Seafoamed through the vacuum lines and crank case
checked my TPS voltage (.985) Tuner said that doesn't matter as it fluctuates
Disconnected my IAC and set the Throttle Stop Screw which I backed off further today

The tuner is one of the best and we are both thinking it's something mechanical...he feels it might be the TB. Anyone have any suggestions???

Thanks

 

[BLKsteeda]

Also, the tuner initially tuned the car at the end of last year and we had a stalling problem for a while which was corrected by bumping up the throttle stop screw. That fixed it for months. This problem started to show up on its own a few weeks ago.

 

[BobHyatt]

That is an issue in the PCM, probably with the tune. The PCM has the ability to say "OK, car is moving, throttle is closed, no sense in dropping back to idle since he is probably shifting..." Once the VSS output shows the driveshaft is stationary, it then decides you really want to idle and back it goes.

I don't know much about how to adjust that, but I have noticed that many stangs behave somewhat like that when the thing is moving. It could be caused by lower vacuum due to the cam, or who knows what else... But something is convincing the PCM to not drop back to idle, which it can control with the IAC.

 

[COramprat]

There was a post here describing the same problem...

Never mind...that was your original post. Still having issues I guess...

My bet is it is still the tuner. Did you go back and read the suggestions in your original post?

 

[BLKsteeda]

There was a post here describing the same problem...

Never mind...that was your original post. Still having issues I guess...

My bet is it is still the tuner. Did you go back and read the suggestions in your original post?

Yeah, went through all those, if I remember right, that's when I was stalling...this is the exact opposite now