2001 ford mustang gt, hunting idle

[Adam Vinnicombe]

Hi all I'm new here and nice to mustangs so please go east on me.
Anyway my 2001 ford mustang gt has an issue with the idle. It will sit for a few seconds at around 750 rpm when hot then all of a sudden it will drop to 500 rpm then rise to 1200 rpm and will keep doing this untill I rev the engine.
Also when I dip the clutch at T junction or come to a stop the engine will stall.
Now it does have a diablosport tune installed and I can change the idle rpm. If I set the idle rpm to 805rpm she is rock solid with no hunting but I believe that 805rpm at idle is to high?
Anyway does anyone know what could be wrong?
Many thanks
Adam

 

[ttocs]

what other modifications have been done to the car? I would probably start by looking for vac leaks by smoke checking it. There are more then a few videos online that show how to DIY with a cigar and some basic parts.

 

[Adam Vinnicombe]

Well I've Been all over the engine today with a few tins of carb cleaner looking for vacuum leaks on the engine and found none.
Here's the engine modification
4.10 gears.
Mac long tube headers.
Pro chamber mac flow exhaust.
Cobra windage tray.
New 11" Cobra clutch.
Svt fuel pumps.
Fms alloy propshaft.
Egr delete.
I do have one more issue as well and that is the engine service light keeps coming on with two code p0153 & p0133 Bank one O2 sensor 1 and bank 2 O2 sensor 1 slow to react.