Need help please

[Teh99SVT]

I'm going to start off by saying I'm not a mechanic, I just love mustangs.
I'm having problems with my cobra's idle.
First, it was idling very low to the point where it would bog and shut off.
After cleaning the MAF and IAC and replacing the air filter, nothing changed.
I took it to a local shop where the mechanic told me my alternator was bad.
He ordered one, replaced it, then figured out it wasn't the alternator.
He told me then I had a bad ground wire.
Instead of ordering a new one, he rigged it to ground elsewhere.
He returned the car to me and it ran perfect for a day.
The following morning, it idled at 3 grand and wouldn't drop any lower.
Driving it back to the shop was a little crazy w/ half open throttle... :fm:
The following week, the car was returned to me working properly.
Mechanic says he messed with the ground and replaced a bad 02 sensor.
Today, the car reverts to acting the same after running correctly for a week.
It starts, idles fine, and gradually idles up to 2-2.5k rpms and holds there.
I have no idea what to do and feel like I need to attempt to fix this myself.
Any info or ideas would be greatly appreciated!!!

 

[01vert]

Get a new mechanic, seriously.

Sounds like this guy is a hack who is just fooling around adjusting stuff and is not helping the situation.

 

[Teh99SVT]

I know there are good mechanics out there but..
The situation has turned me off of mechanics.
I am also hesitant to drive the car any considerable distance.
Any idea what can cause this problem?

 

[Un4GivN]

These cars are notorious for IAC problems. So long as your throttle isn't sticking open, I think it's safe to assume your IAC is the issue.

 

[99MystiC]

These cars are notorious for IAC problems. So long as your throttle isn't sticking open, I think it's safe to assume your IAC is the issue.

+1
What happens when u rev it, does the idle hang up high an slowly come down?

 

[Teh99SVT]

Anywhere I rev to it drops back to 3 grand, hangs for prob 5 secs.
Then quickly drops to around 2200 and holds its idle there.

 

[DuffManRHA]

It really sounds like a vacuum leak now, maybe he messed with something, IAC, etc. and the gasket is messed up, or maybe he just hit a hose and knocked it off. From the sound of this mechanic, it wouldn't be outside the realm of possibility either.

Also check the FPRS (Fuel Pressure Rail Sensor) by disconnecting the electrical connection, but leave the vacuum connection alone, and see if that helps. Might also want to clear the computer too, but I really think its a vacuum leak from the symptoms.

Eric

 

[Teh99SVT]

I appreciate all of the info! :bowdown:
I'm currently on orders but I will try this
and see what happens when I get back home.
Thank you all and I'll be back on if I have more questions.

 

[PSUCOBRA96]

clean the IAC, also take the back of a screwdriver and lightly tap the MAF, see if the motor starts acting funny, if so the MAF could be bad as well. Use electrical parts cleaner on the MAF and carb cleaner on the IAC

 

[gmsux]

Perhaps verifying base idle is correct is in order.

With the engine idling, remove the IAC connector, if the engine dies, then turn the T/B idle screw in one turn at a time util the idle is at the desired level. Then adjust the TPS sensor to .96-.98 volts on the grey/white wire with ignition key on. You may have to drill the TPS holes out slightly. After this, disconnect the battery and tap the brakes a couple times to discharge any voltage and clear KAM memory and reconnect in 10 minutes. This procedure will properly set your base idle.

 

[Teh99SVT]

So.. it turns out my throttle position sensor was broken.
I have no idea how this could happen but apparently it can.
After replacing the sensor everything is running smoothly.
I believe the sensor could not retract to where it needed to be at 0 throttle.
Like i said, this fixed my problem so if you ever have similar problems...
Check it out! Thank you all for your help and be safe! :rockon: