[Moot88]

Ok so here is my problem, my mustang has been stumbling off and on for awhile now and i cant figure it out Sometimes it will run great , then the next time i start it will run like crap.... I have changed plugs, wires, cap, button, coil, fuel filter. I have a fuel gauge and im running 35 at lidle and up to about 43 getting on it... I was told that if u unplug the iac while at ilde and it doesnt change that it's bad??? I know i just gave my life story just looking for some input thnx guys.

[fogged306]

Are you talking abou it stumbling at idle, or while driving or both? IAC is only for idle, so if you're having issues with driveability, then you have more issues than just a possible bad/clogged IAC. ... Check engine light on?

[VM0824]

i had similar problems. poor response. general sloppy idle. while cleaning the iac with carb cleaner is def a possible solution, i found that changing the Air Charge Temperature sensor and the Engine Coolant Temperature sensor made a HUGE difference in performance. night and day. the ACT gets fouled after it gets coated with carbon buildup and the ECT is too cheap/easy to not try replacing.

total cost mayb $35

when the sensors are bad, the computer is calculating air/fuel ratio with incorrect numbers and you end up with a poor running engine

[Moot88]

I'm having problems at idle and driving. Thing is that it doesnt do it all the time hit and miss kinda thing. No check engine light on either. Its a wierd stumble i dont see my rpms drop at all idk if its such a small stubble that i just cant see it on gauge.

[VM0824]

Definitely try those sensors. When they foul the engine runs sloppy

[fogged306]

Have you covered the basics? Like fuel and air filter, checked plugs, cap, rotor, wires, ect..

[Moot88]

VM0824 thnx. I will check into those. Fogged306 yea i changed it all. If i change those sensors will that throw off my tune?

[Moot88]

btw it only does it while driving. I dont get it if i just rev it or give it gas in netrual it does fine. If that makes any sense.

[Cschneider_23]

where is the ACT or What is it

[Jordan_m6]

I'm pretty sure its located behind the upper intake somewhere.



*EDIT* Nevermind, I don't think that sounds right.

[VM0824]

its right behind the distributor on the lower intake, under the upper intake. sits kinda next to the front fuel iinjectors. its measures the temperature of the incoming air and sends that to the ecu.

physics lesson. the hotter the air, the less dense it is, and therefore the less actualy air molecules available for combustion per unit volume. by knowing the temperature of the air, and adjusting the air/fuel ratio accordingly, the computer has a better chance of maintaining stoichiometric levels.

when the act gets buildup on it, the temps it sends to the comp are off, therefore the ecu compensates incorrectly for air temp. i dont think changing this could screw up your tune, it will only give more accurate information to your ecu

[sixtang]

Could it be a MAF sensor? If the wireing or connector is loose/corroded or the sensor is shot it might cut in and out. Just a thought.

[VM0824]

Originally Posted by sixtang Could it be a MAF sensor? If the wireing or connector is loose/corroded or the sensor is shot it might cut in and out. Just a thought.

yea, while idle, pull wiring connector from maf and you should def notice idle change or even a stall. if nothing happens you may have maf prob

[VM0824]

its the thing with the brass colored bottom hex nut

[Moot88]

Ok i changed the act sensor and it was built up bad with carbon so i thought that was it, and no change.. Cleaned the maf with maf cleaner. So i guess i need to change the ect sensor but dont know where it is located. If anyone has any more ideas plz let me know thnx

[VM0824]

did you disconnect battery for awhile?
do a dark spark test. Wait til night, or if you can get your garage very dark. Let engine run and look for blue sparks. Sometimes they jump from wires to the header. I had a coil with a microscopic crack that you could see lighting out of only in pitch black. That'll def cause a stumble

[Moot88]

Yea i unhooked the battery for atleast a half hour or so. I will do the spark test for sure. I sanded all ground wires also. I heard possibly a TP sensor could do it also? I dont think its a vac leak cause on my boost/vac gauge is steady? Dont really know what the numbers should be tho.

[VM0824]

hmm. im not positive but if the tp sensor was bad it would only idle rough or idle high, like the comp would think your giving it gas? idk, i had to fix mine once. Ford Fuel Injection is a GREAT resource for testing voltages on sensors. that link is to the tps page.

ive heard you can test for vac leak by leaking something flammable near possible leaks, like propane. but ive always been to afraid to so i spray carb cleaner on hoses and listen for idle changes.

[VM0824]

also, i know you said no check engine light, but that doesnt always mean the computer doesnt have codes. put some miles on it, (since unplugging the battery would have reset them, sry i didnt think of this before) and then run the self test anyway to see if any codes pop up