i did a trickflow hci swap with stage 2 cam 30lb injectors 70mm throttle body blah blah 190lph pump. had idle surging problems, went away by cranking idle screw intake started whistling but didnt die as soon as the car warmed up. Got car dyno'd last week pretty happy with the power 299hp 306tq. But now when im driving and push in the clutch and let rpm fall it will either die or drop to 500rpm then surge to 1500 then level out after 10sec, only when the car is warm, any ideas on what it could be, tps is good new ford iac new msd dist. w/sensor the car is converted to maf computer is a A9L. Is the bap sensor supposed to have vac. tube hooked up or not it is not now. car has smog delete. I did not run vac line from throttle body to filler tube? could that be it? At wot the car hauls @ss. If we didnt have stupid stop signs this would never bother me
your car uses the VSS and IAC during deceleration. if your IAC checks out fine, i'd check the VSS. does your speedo work? even if your speed sensor works fine, if it doesn't have a speedo gear spinning it to let your ecu know how fast the car is going, it'll cause your car to stall like yours is doing.
See the "Surging Idle Checklist for help with all your idle/stall problems. The first two posts contain all the updates to the fixes. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.