dadirtypoostick

I am getting a bit of a rough idle especially when using the a/c. It isnt really rough, more like a pulsing up and down 250 rpm. I have checked for vacuum leaks put havent found any. Also getting an "idle air rpm lower than expected" trouble code. Could It be spark plug related?

2005 Gt, 56k miles. CAI and tune are the only mods so far. thanks

moosestang

Not likely the spark plugs. It's probably the throttle body itself or one of the sensors on the throttle body like TPS or the IAC sensor. I would first remove the throttle body and clean it. Your idle shouldn't fluctuate that much. Mine is always 750rpms +/- 15rpms.

Are you the original owner? Just want to rule out the notorious BBK throttle bodies which suck.

If you had a vacuum leak big enough to affect the idle, it would throw a lean code, IME.

dadirtypoostick

Im not the original owner but I am fairly certain everything on the car is stock. I am going to go ahead and try to clean it. The biggest fluctuation happens when the a/c is running. Is there anything I can check there, or is it just because it is putting a load on the engine? also the fluctuation is closer to 100 to 150 rpms

Nuke

+1 on the TB first, then replace the fuel filter. After that, it gets a bit more expensive.

JCON

You mentioned you have a CAI, is your air tube that connects to the passenger side from the intake connected?

moosestang

It's just because of the increase load. The throttle body is easy to remove and don't ham fist the nuts/studs putting it back on. They only call for 89 inch lbs.

Do what Nuke said and replace the fuel filter.

How does the car feel when cruising or WOT?

dadirtypoostick

I will definitely do that Monday. At a quarter pedal and low speeds the car feels as though it bogs down but I thought that was the way the tune was set. at 3/4 to full pedal it would scream but since the fluctuations started I have been taking it easy. Now that I think of it, she used to bark the tires when shifting to second and third, on a good day 4th (AT) A couple of weekends ago I barely got it to burn out really good showing the car to my dad. This past week is when the flux was noticeable, I would definitely say it has a small loss of power. Feels worse in the lower speeds and rpms.

Where is the fuel filter located at? Its my first mustang, and newest car to date. (Please dont say in the tank....)

dadirtypoostick

I do have the hose connected. the only thing I can see that I did "wrong" is that I used the factory screws for the MAF sensor when the instructions said not to. Don't know what the difference is but the aftermarket screws weren't in the box.

moosestang

The fuel filter is under the car on the drivers side frame rail, right below the drivers door. You'll see a long black piece of plastic with a few screws, it's under that. It has quick disconnect fittings on both ends, so it can be changed with just a flat head screw driver.

Be sure the car has sat over night, so that there is no pressure in the fuel line or you could pull the fuel pump fuse and crank the motor a couple of times. The fuel pump can be accessed from inside the car under the rear seat, no need to lower the tank. That's one of the things Ford got right on this car.

I'd get a genuine motorcraft fuel filter, so you'll probably have to go to the dealer.

Nuke

The change in the ability to smoke the tires over time can be due to many things. As the weather gets warmer (and you're in GA), these engines will heat soak and lose a large % of power. Ever notice how quick the car is in the winter compared to summer? Also, the PCM has an adaptive learning feature which will essentially set a number of performance parameters at below-optimum values for performance for the sake of economy. Disconnecting the battery for about 30 minutes every so many months often wakes the car back up (sometimes it takes about 20-50 miles of spirited driving to even out how the engine runs but it's worth the effort). And then there are all the other issues...