Idle creeps up question ??

Mustang_289 · 03-07-2002, 07:52 AM

Our stang will start out idling fine - but you let it run and the
idle creeps up almost to 2K. Any thoughts on what is causing it, would the likely candidate be the idle sensor attached to throttle body?

PKRWUD · 03-07-2002, 10:22 AM

I doubt it. What year/make/model/mods? Any codes? recent tune up? Any other problems? When did this start?

Mustang_289 · 03-07-2002, 11:08 AM

Recent tune-up: new plugs, wires, cap & rotor, timing.

88GT speed density.

Mods: MAC longtube headers, underdrive pullies, Black Magic flex-a-lite electric fan, K&N.

Problem has been here for a while. My son and I bought this stang pretty much in pieces and we're putting it back together.
someone mentioned it could even be the EGR causing the idle to creep up. Don't know about any codes or how to even check the codes.

Thanx for the help

Old Guy with 87 GT · 03-08-2002, 12:02 AM

probly not the egr,mine's been discenected for quit some time ,no mager impact.........

check the voltage at the tps (throttle position sensor).....should be .95 - .98 volts...........

see where the throttle stop screw is set .......the computer sets the idle ,but if somone cranked up that screw it'll still idle high............

also look for vacuum leaks ........

good luck

Mustang_289 · 03-08-2002, 07:53 AM

Thanx for the info! If the tps voltage is not between .95 - .98, is there an adjustment somewhere - or does that tell me the TPS is bad?

Old Guy with 87 GT · 03-08-2002, 12:49 PM

yes they can be adjusted,the two screws fastening it can be loosened and it has a little play in it.......

the stock setting for the tps is a little lower voltage ........i'm not sure but i think the stock guidlines to tell you if the tps is good is like .75 to 1.0 volts .......

seting it at .98 is like a performance trick and thats the setting most guy's use...........if the voltage is around there then chances are it's not your problem

if you find that when you adjust it ,you can't get it to .98 ,then you can take a drill and elongate the holes a little to give the tps a little more adjustment room.....i just replaced mine and had to do this to get .98 .........when i set up my idle took a couple of times to get it to idle where i wanted it ..........you have to set the throttle stop ,then adjust tps .......when i did mine i adjusted the throttle stop to get the idle where i wanted it then went back and set tps

unless somone cranked up the thottle stop screw to compensate for another problem,you shouldn't have to reset it ........the air control valve (cylinder on side of throttle body) basicly controls idle ,it does this by adjusting the amount of air going in ,the computer alows a set amount of air and then adjusts injectors to find the right mix ........if the thottle stop is set to high then to much air will enter thottle body and the computer will compensate by setting the air- fuel to what air it has to work with..........so basicly if you turn that thottle stop screw up it lets to much air in via the main ventura and the computer can't control idle with the control vale ,it'll close the valve and and there will still be to much air going in moter..........if you have a vacuum leak of if the idle control valve is gumed up and can't close all the way...it'll cause the same problem...........

illiminating the the tps as the problem is just a matter of checking to see if it's voltage output is well above normal.........the tps tells the computer where the gas pedal is at ,if it puts out to much voltage the computer will compensate by thinking that your pushing the gas pedal down some and the carts not at idle

#1--if you check the voltage at the tps and it's not out of range by a large margin ,#2--then check the idle control valve make sure it's closing all the way (take it apart clean it out ),#3-- check to see if the set screw is holding the main butterfly open too much (turn set position to close it more,see if it changes idle )#4--check for vacuum leaks ..........if your idle is still high after illiminating all the above then another sencor must be giving the incorrect readings making the computer think runnings conditions are wrong

well good luck ,hope i was able to help

03-08-2002, 12:49 PM	#6
Old Guy with 87 GT Registered Member Join Date: May 2001 Location: Harrisburg, Pennsylvania Posts: 379	yes they can be adjusted,the two screws fastening it can be loosened and it has a little play in it....... the stock setting for the tps is a little lower voltage ........i'm not sure but i think the stock guidlines to tell you if the tps is good is like .75 to 1.0 volts ....... seting it at .98 is like a performance trick and thats the setting most guy's use...........if the voltage is around there then chances are it's not your problem if you find that when you adjust it ,you can't get it to .98 ,then you can take a drill and elongate the holes a little to give the tps a little more adjustment room.....i just replaced mine and had to do this to get .98 .........when i set up my idle took a couple of times to get it to idle where i wanted it ..........you have to set the throttle stop ,then adjust tps .......when i did mine i adjusted the throttle stop to get the idle where i wanted it then went back and set tps unless somone cranked up the thottle stop screw to compensate for another problem,you shouldn't have to reset it ........the air control valve (cylinder on side of throttle body) basicly controls idle ,it does this by adjusting the amount of air going in ,the computer alows a set amount of air and then adjusts injectors to find the right mix ........if the thottle stop is set to high then to much air will enter thottle body and the computer will compensate by setting the air- fuel to what air it has to work with..........so basicly if you turn that thottle stop screw up it lets to much air in via the main ventura and the computer can't control idle with the control vale ,it'll close the valve and and there will still be to much air going in moter..........if you have a vacuum leak of if the idle control valve is gumed up and can't close all the way...it'll cause the same problem........... illiminating the the tps as the problem is just a matter of checking to see if it's voltage output is well above normal.........the tps tells the computer where the gas pedal is at ,if it puts out to much voltage the computer will compensate by thinking that your pushing the gas pedal down some and the carts not at idle #1--if you check the voltage at the tps and it's not out of range by a large margin ,#2--then check the idle control valve make sure it's closing all the way (take it apart clean it out ),#3-- check to see if the set screw is holding the main butterfly open too much (turn set position to close it more,see if it changes idle )#4--check for vacuum leaks ..........if your idle is still high after illiminating all the above then another sencor must be giving the incorrect readings making the computer think runnings conditions are wrong well good luck ,hope i was able to help __________________ the "not so old",old guy 87 Mustang GT T-top >hanlon t-5, pro 5.0, centerforce clutch ,adj. cable/quatrant ,3.27s ,full 2 1/2 ex(off road H) adj. reg. ,e-cam ,70mm TB, cobra intake ,1.7rr ,ported/milled e7ets w/crane springs ,306 balaced/decked short block w/speed pro forged flat top pistons ...257rwhp/302rwt best et 13.7@102 (4/11 ) '80 Capri (future project,currently collecting parts for 351 moter)

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03-07-2002, 07:52 AM	#1
Mustang_289 Registered Member Join Date: Sep 2001 Posts: 512	Idle creeps up question ?? Our stang will start out idling fine - but you let it run and the idle creeps up almost to 2K. Any thoughts on what is causing it, would the likely candidate be the idle sensor attached to throttle body?

03-07-2002, 10:22 AM	#2
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	I doubt it. What year/make/model/mods? Any codes? recent tune up? Any other problems? When did this start? __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!

03-07-2002, 11:08 AM	#3
Mustang_289 Registered Member Join Date: Sep 2001 Posts: 512	Recent tune-up: new plugs, wires, cap & rotor, timing. 88GT speed density. Mods: MAC longtube headers, underdrive pullies, Black Magic flex-a-lite electric fan, K&N. Problem has been here for a while. My son and I bought this stang pretty much in pieces and we're putting it back together. someone mentioned it could even be the EGR causing the idle to creep up. Don't know about any codes or how to even check the codes. Thanx for the help

03-08-2002, 12:02 AM	#4
Old Guy with 87 GT Registered Member Join Date: May 2001 Location: Harrisburg, Pennsylvania Posts: 379	probly not the egr,mine's been discenected for quit some time ,no mager impact......... check the voltage at the tps (throttle position sensor).....should be .95 - .98 volts........... see where the throttle stop screw is set .......the computer sets the idle ,but if somone cranked up that screw it'll still idle high............ also look for vacuum leaks ........ good luck __________________ the "not so old",old guy 87 Mustang GT T-top >hanlon t-5, pro 5.0, centerforce clutch ,adj. cable/quatrant ,3.27s ,full 2 1/2 ex(off road H) adj. reg. ,e-cam ,70mm TB, cobra intake ,1.7rr ,ported/milled e7ets w/crane springs ,306 balaced/decked short block w/speed pro forged flat top pistons ...257rwhp/302rwt best et 13.7@102 (4/11 ) '80 Capri (future project,currently collecting parts for 351 moter)

03-08-2002, 07:53 AM	#5
Mustang_289 Registered Member Join Date: Sep 2001 Posts: 512	Thanx for the info! If the tps voltage is not between .95 - .98, is there an adjustment somewhere - or does that tell me the TPS is bad?