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Fast Idle
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Posted by: trainmstr

Have (2) 1999 Mustangs with same problem, idle speed is getting faster and faster as time goes by. Is the throttle position sensor going bad, or something else? Last two weeks gas milage has taken a nosedive too due to the fast RPMs. Any ideas appreciated.

Posted by: Jimbo_Jack

check that sensor...i had the same problem with my 1968 mustang...but that was an easy fix and a totally different than the 99...

Posted by: kissajew86

also get some electrical cleaner and check the maf....make sure it is electrical cleaner so it does not leave any residue....

you can check the tps with an ohm meter if you have one....remove the sensor and vary the position of the sensor and the ohmage should change gradually with no spikes.....just like a variable resister....

if you have no idea what i am talking about then nevermind....

Posted by: badass98svt

do all of the above (especially the tps). just go to the junkyard and buy a couple for $5 and try it on your cars to see if it fixes the problem. if not clean the MAFS and also clean the IAC. that should fix the problem

Posted by: trainmstr

I understand how to check the TPS and have done so in the past, will get to it this weekend. When you say electrical cleaner do you mean TV Tuner cleaner??? I know what a MAFS is but what is the IAC?
Thanks for responses.

Posted by: badass98svt

the IAC is the Idle Air Control valve. it a cylinder looking piece that's located by the upper plenum. it's attached with two 10mm bolts and has one small harness connected to it. remove the IAC and spray inside the holes with throttle body cleaner. fill the holes up, put your palm over them and shake the IAC. pour the T.B. cleaner out and repeat 2 or 3 times. reinstall it and start the car up and enjoy your new smooth idle. lol
btw, your IAC looks exactly like this.
http://cgi.ebay.com/ebaymotors/Grand...spagenameZWD1V

btw, as far as electronic parts cleaner goes, i use "air intake cleaner".

for the MAFS, get the special bit to remove the MAFS and remove it. The bit is a T-20 torx bit with a hole in the middle (it's name is a T20H). it's readily available at Sears. hold the sensor about 12-15" away from the can and spray it with the air intake cleaner, or you can spray a Q-tip and GENTLY clean the sensor with the Q-tip.

Posted by: kissajew86

when i say electrical cleaner i mean some thing like this. It is very quick and easy to use, i got mine at autozone, it sprays it so you do not have to dissasemble the maf, you can just douse it well and it gets really clean.

If you have a k&n that tends to get oil on the maf, this will clean it up really well.

http://www.midwayautosupply.com/deta...ption.asp?3769

Posted by: speedytang

If you put the car on a OBDII tester it will probably narrow it down. My '89 5.0 is doing this now and my error list is huge(30). I am going to clear and see what I get after 10 minutes of run time. I replaced my MAF, I swapped the IAC and no change. My problem started when I switched to a 130amp alternator and even if I unhook it the car still does the high idle and it shows lean but is rich so I am going to unhook my O2s and let it run in limp mode to see if it changes operation. I usually have these things figured out in minutes and this one has lasted 1 week. My mpg went from 21mpg to 9mpg when I took it for a drive yesterday.

Posted by: trainmstr

Thanks for providing additional info. Will work on car #1 this weekend.

Posted by: badass98svt

train, be sure to let us know how it goes. everything i mentioned won't take more than 15 minutes. if it doesn't fix it, get back here and tell us.

Posted by: trainmstr

I cleaned the MAFS and IAC, idle is now fine. Have a new problem, engine is detonating real bad under load at approx 2500 rpm and gas milage is still real bad. Not getting any codes, could it be the oxygen sensor????

Posted by: kissajew86

engine detonation could be a couple of things. Carbon build up in engine, bad spark plugs, bag gas (you may have some watter in there), lean a/f ratio caused by o2 sensors, maf, air leak....

i would start with the cheap stuff first...

Posted by: trainmstr

Anybody ever do a seafoam treatment on their Mustang? I was just reading about it on an Explorer forum, everyone there swears by it. I would think that would take care of the carbon issue. Will try new plugs, gas is good filled two cars at same time, same station, same gas, no problem with other car. Will start new thread on seafoam.

Posted by: badass98svt

be sure to change your plugs and oil after using the seafoam.

Posted by: kissajew86

I have used seafoam, it looks like it works with as much foam that pours out