leamangriffin

I have a 99 Mustang gt vert. It has an 03 Gt motor in it. Automatic. BBk intake system, shift kit, bbk shortys, bbk o/r x pipe with no cats, and thrush welded mufflers. I had a small idling problem a while back... it would surge and drop 10 times, then return to normal, then it would repeat... so I got to looking and heard about the IAC problem. I bought a new one. replaced it. While I was at it I took off my TB and plenum, cleaned both out to remove all the carbon, cleaned the maf. then reinstalled.. also I disconnected the batt... ran fine for a few days... Then it started acting up... I would press the gas and let off and the rpms would stay at 1.5k- 2k for about 5 seconds, then it would return to normal... It only did it when I was in drive or reverse.. When I put it into park it would idle at 900 rpms and slowly climb to 1k-1.1k...

I replaced the TPS sensor. no help... one day I started it, and it idled fine, then I put it in reverse and the revs went to 1.5K then 400, then 1.5K then 400, then 1.5K then it stalled. I started it back up and no problems... then a day later it started acting up again. So I thought it the IAC i got was bad. so I swapped it out... got the new one in. unplugged the batt... and while it was unplugged, i reset my idle set screw. used a .10 feeler, then tightened 1.5 turns. then i connected my batt, started my car with the iac unplugged. set the idle to 800 then shut it off, plugged in the iac, then restarted. i let it idle for 10 mins, then turned on the ac and let it idle for 10 more. then i gave it some throttle and it hung at 1.5k then died. also I checked my tps voltage and i set it at .98 - .99 .

I thought maybe a vacuum leak, so i started checking, I found a small rip in the pcv hose so I replaced it.. then i noticed that when idling the vacuum sucks the pcv hose flat. and when i turn the car off it returns to round. this still didnt fix my idle problem. so I thought it might be the pcv valve. I took it off and it rattles like normal. I sprayed som carb cleaner in it and reinstalled. I have tried resetting with the battery multiple times and nothing is working. I can get it to idle normal everytime, but then when i try to give it gas it hangs up then dies. I tried to install the IAC plate that reduces idle hang, and now the idle is always at 1200rpms. even when i back the idle set screw all the way off. It is not my throttle cable because when it hangs i push the butterfly closed and it doesnt go down. It seems like when i disconnect the IAC I can get it to rev without hanging, but I havent tried driving it like this. also I disconnected the IAC connector while idling and it still runs at like 600rpms, then i pull the hose off and put my finger over the iac and the idle doesnt change.... but it does create suction on my finger... isnt it supposed to be closed when unplugged? then i plug the connector back in and it idles fine with my finger plugging it, but when i remove my finger the car stalls..... I am at a complete loss.... and help would be great...

leamangriffin

A video of what it does...

http://www.youtube.com/watch?v=aBkUWK4ojPk

Repzard

Well one thing I see from your many pics(last one mostly) is that the adjustment screw on TB was played with. (looks like someone took pliers to it by the marks on it) my guess is that is your issue. TB isnt closing enough and adjustment screw is set too far and keeping it open more than it should causing idle to stay up.

Could be wrong but it looks played with and set too far in my guess
Just my 2

GL

uberstang1

That adjustment screw def looks pushed way out, try screwing it back in and wash that poor engine bay.

cliffyk

You said you used a 0.10 feeler gauge to set the throttle stop screw (it is NOT an idle adjustment)--I assume you meant 0.010"? Also, 1-1/2 turns after setting the 0.010" clearance is too much, 1 turn is correct (read more here).

As stated above the stop screw on the TB is not an idle adjustment, the only way to change the idle speed is by changing the scalar values in the tune. Your attempting to set it as you said ("started my car with the iac unplugged. set the idle to 800 then shut it off") has likely completely fouled up the initial setting--re-do it as described in the link above.

The TPS is not adjustable and does not need to be adjusted on the EECV system, the PCM continuously learns the lowest observed value as being closed throttle. I am curious as to how you adjusted it as the range of motion is very limited--the mounting holes are not slotted?

The IAC is not completely closed when unplugged...