idle problem

[90 GT]

i own a 1990 gt and have a problem with it idleing steady.the gt basically for now has mac long tube headers and 373 gears in the back.i just gave it a fresh tuneup (plugs wires distributor cap and rotor).i tried adjusting the throttle screw and i brought the idle up to 1000.like a few days after the revs dropped to about 600 and it goes up 800 and back down again ,i have no idea what would cause it to do that.any help out there i'd really appreciate it. thanks

 

[HISSIN50]

the computer will adapt. so if you manually raise the idle, it will eventually figure it out and try to get it back down to stock idle specs. because things are out of whack, it can cause surging and other issues.

some have disconnected the IAC - i have not and dont know how effective that is.

just some info. good luck.

 

[blackstangt]

it's not supposed to be at 1000 at idle. The computer is adjusting to get back down to 650-700 rpm which is the comp set idle. Also, try disconnecting the neg for 15 mins, and set the idle to 700.

 

[gungfusemaj]

Black is right 700 Rpms make sure your TB sensor is set at the right voltage.

 

[bsedwebt70-5.0]

clean your tps - take off your air intake tube that goes to the throttle body and go to town - you will find if you pull off that little 2 bolt on thing at frt of the throttle body area that allows the gas to return (EGR) it will be coated in carbon inside - take it off and clean with carb cleaner - works every time - takes about 10 minutes with an old toothbrush and rags - I wish I knew better how to describe it

 

[ironmedic]

also check your TPS voltage!

 

[88_GT_5_oh]

try this.. it worked for me when i had this problem

http://www.fordmuscle.com/archives/2002/01/tenpin/index.shtml

 

[90 GT]

guys thanks alot for the help.i still have a problem with the tps sensor reading at 1.1 instead of it being in the .98 .99 range.i cant get it to go any lower than 1.1 and i don't know what to do next.

 

[$uperstang]

I had the same problem with mine. If your car is surging at stop lights (funny idle) just replace the TPS all in all and you'll be fine.

 

[HISSIN50]

guys thanks alot for the help.i still have a problem with the tps sensor reading at 1.1 instead of it being in the .98 .99 range.i cant get it to go any lower than 1.1 and i don't know what to do next.

IIRC, the puter zeroes the TPS reading out at start up, each time. as long as the static reading is ~1.30 volts or less, it is immaterial (per Michael and Stang & 2 Birds).

that said, some have diminished surging and such, by dialing the static TPS reading down from slightly over 1 volt to below.

good luck.