what is causing this crazy idle?!

[the98stang]

So I have been to hell and back with my GT. Sometimes when I am driving the idle will drop to 200-300 rpm's and then back to normal, but it only happens when I come to stop. No engine codes. I replaced the IAC with a motorcraft. I have new plugs. A new PCV/grommet. New fuel filter. I cleaned the MAF. I'm not sure when the problem started though. All I have on the car right now is exhaust and gears. I do hear a "hissing/pshhhh" kind of noise from the rear of the intake manifold. So I sprayed carb cleaner in the area to look for vac leaks. But I had no luck. Could a vacuum leak cause a problem like this? I think a vac leak would cause a continuous problem, not something like this random idle that doesn't happen all of the time. I did data log the car (xcal2) but I can't understand it that well, so I could send you the file if you want. I have a few suspects:



Vac lines (hissing noise)

o2 sensors (stockers, 75k miles, X-pipe)

TPS (replaced with one from Autozone)

Engine coolant temperature sensor (I thought 00's had a TSB on this)

Bad/not updated PCM (I thought I heard the 99-00 had troubles)



So any ideas? I would appreciate the help! It's driving me nuts Thanks...



Tanner

 

[RedDaemon]

the iac that u replaced it with might be bad

 

[LaserRed01GT]

Vacuum leaks rear their ugly head mostly at idle when the throttle blade is closed and aren't always consistent. You can send me the data log file(csv) and I will take a look at it. Did you do the logging when it was doing this at idle?

 

[Mike97gt]

check your vacumm lines and air inlet tube after the maf. if you can pull live data take a look at your longterm and short term fuel trims. Post the info on here if you have it.

 

[the98stang]

http://www.geocities.com/mo0cow2003/test1.txt
http://www.geocities.com/mo0cow2003/test2.txt
http://www.geocities.com/mo0cow2003/test3.txt

Try those and change the file to (csv).

 

[RandyStinchcomb]

I'd put the oem TPS back on, as the Ford TPS on our cars has been one of the MOST Trouble Free TPS Ford has ever used. I had someone else on abother board who did the samething, he put his oem TPS back on and the problem went away.
oh and the PCV valve you replaced, was it OEM or somemore aftermarket crap?

 

[the98stang]

OEM pcv

 

[Jakes]

By any chance, have you removed the screen just ahead of the maf. If so, put it back in and see if that solves your problem. Let us know,

 

[LaserRed01GT]

Well your Bank 1 upstream O2 sensor looks like it's going lazy. There is also a prolonged instance when Bank 1 AND Bank 2 STFT's are going opposite ways. Bank 2 is pulling fuel and Bank 1 is adding fuel.

There are also several instances when your Bank 1 upstream O2 sensor voltage goes very low (below 100), and the IAC opens up more than normal to try and compensate.

Without being able to watch this full time with my Solus, I would recommend replacing the Bank 1 Sensor 1. I would also agree with Randy that you should put the OEM TPS sensor back on, if it's still good. They rarely fail, I have only seen one bad TPS sensors on these cars in a long long time.

 

[the98stang]

Well your Bank 1 upstream O2 sensor looks like it's going lazy. There is also a prolonged instance when Bank 1 AND Bank 2 STFT's are going opposite ways. Bank 2 is pulling fuel and Bank 1 is adding fuel.

There are also several instances when your Bank 1 upstream O2 sensor voltage goes very low (below 100), and the IAC opens up more than normal to try and compensate.

Without being able to watch this full time with my Solus, I would recommend replacing the Bank 1 Sensor 1. I would also agree with Randy that you should put the OEM TPS sensor back on, if it's still good. They rarely fail, I have only seen one bad TPS sensors on these cars in a long long time.

I will check to see if I have the stock TPS installed. If it isn't, I'll put it back in.

I got a butane torch to check for vac leaks so I'll see how that goes.

Does any one have the motor craft part number for the Upstream bank 1 o2 sensor? I'll replace it and see if it helps. Thanks for the input.

 

[RandyStinchcomb]

Does any one have the motor craft part number for the Upstream bank 1 o2 sensor? I'll replace it and see if it helps. Thanks for the input.

Ford part # F5MZ-9F472-AA & Motorcraft part # is DY-761

 

[the98stang]

OK I replaced the bank1 upstream sensor. The old was WHITE as hell. The bottom portion of the sensor was black, but most of it was white. I'm assuming this means lean conditions. I'm pretty sure I have an exhuast leak because I can hear fluttering near the engine whenever I give it gas (I had a X pipe and catback). Do you think this could cause the idle conditions?

The car definetely runs better with the new o2 sensor. However the idle problem still occrus every once and a while. I got the stock TPS back on. I have a boost gauge and the vac is reading about 17-20. Soon I will have my AFR wideband going as well. Any other suggestions?

 

[the98stang]

no one?

 

[Mike97gt]

if you have a exhaust leak near the front 02's that can cause issues like you are having, fix the exhaust leak then see how it runs.

 

[the98stang]

if you have a exhaust leak near the front 02's that can cause issues like you are having, fix the exhaust leak then see how it runs.

I will get the leak fixed. I have a new gasket installed, so what else can I do to get rid of the leak?

 

[Yellowfever]

I have the same problem...

Hi. I have a 2002 gt with saleen supercharger, the problem is when i acelerate and press the clutch, RPM goes too down, the car try to stabilize the idle and in many cases the car die. I thought the same that perhaps it has some leak but i do not find it. Do You think maybe it is some parameter in xcal2. Thank you.

 

[propellerhead]

I get the crazy idle in the morning when I first start the car. I wiggled and pushed in all the vacuum lines and it quit. You have to find the small vacuum lines too. They are usually wrapped in the plastic ribbed tubing.