[mechanic47]

My 87 shelby z kept idiling about 1500 rpm after coming to a complete stop,it gave code 15 so i replaced the speed sensor,still did it ,so I pulled the ais off a wrecked 88 automatic daytona es car,and the problem was fixed.It started doing it again a few weeks later,so I pulled the brake booster hose off to reset the ais,but the ais motor wouldn't pull the idle down like it should.My question is,can the ais go bad and not show any fault codes? I only have the 55 code....thanks.........I pulled the ais off and have a friend turn the switch on and it felt like it was vibrating but the pintle didnt move,and you can't move it with pliers...the other one that was on the car first,you can push the pintle in and out with no resistance......what is supposed to happen when you turn the switch on with the ais off the car?

 

[NAJ]

Yes the AIS can go bad without setting faults, as long as the idle speed is in the controllers range no code will be set.
DO NOT unplug the AIS connector while the controller is attempting to move it or damage to the drivers in the controller may occur.
That is why you wait 60 seconds after creating the large vacuum leak, the controller will be attempting to lower idle by stepping in the pintle, after 60 seconds the AIS will be at 0 steps and no longer moving.
The controller actually has no idea where the AIS steps are, it assumes it is correct.
Thexton makes an AIS tester that will move the pintle in and out.
Do you have a T-1 or T-2? I can post the circuit test.

 

[mechanic47]

Yes the AIS can go bad without setting faults, as long as the idle speed is in the controllers range no code will be set.
DO NOT unplug the AIS connector while the controller is attempting to move it or damage to the drivers in the controller may occur.
That is why you wait 60 seconds after creating the large vacuum leak, the controller will be attempting to lower idle by stepping in the pintle, after 60 seconds the AIS will be at 0 steps and no longer moving.
The controller actually has no idea where the AIS steps are, it assumes it is correct.
Thexton makes an AIS tester that will move the pintle in and out.
Do you have a T-1 or T-2? I can post the circuit test.

I have a t-2,I waited about 2-3 minutes for the ais and it never started to lower the idle when I made the vacuum leak,so I just replaced the vacuum hose,I ordered a new ais this morning and it will be back this evening,thanks for your help and I'll post how it does with the new one

 

[NAJ]

When you create the large vacuum leak you will not see the idle lower until you disconnect the AIS connector and reinstall the vacuum line, then the AIS should be at 0 steps and you will be at base idle.

 

[mechanic47]

Well I replaced the ais motor,and nothing changed,now the code 15 is back for the speed sensor,WHICH IS ONLY ABOUT A MONTH OLD...........anyone interested in a shelby z? with about $1000 in new parts,includind a 1988 es parts car with motor and trans,an 86 parts car wit not much left,and another spare turbo engine,extra crab wheels,guages,odds and ends?....Car has no rust,nice interior,all windows lights etc. work,have a set of louvers for it,needs paint,clearcoat bad in a couple places,have a few dings and dents but looks nice...in Morganton,N.C.