problems with the car...crap idle

the98stang · Nov 9, 2006

First off this is post # 1000, and I'm glad to be a part of :SNSign:

Well I'm still having problems with my car. When I'm coasting and put the car in nuetral, the RPMs will drop to like 400 and then shoot back up to 7-800. Sometimes the car will die. This happens when coming to a stop as well. But the problem isn't ALWAYS there, it happens a few times a week (which makes me think it isn't the vac lines). I put in a new PCV and grommet. That didn't help. A new fuel filter didn't help either. It has a brand new TPS. I replaced many hoses as well. I thought maybe my FIPK was the problem, so I put the stocker in. That didn't help. Then I tried the old IAC. That didn't help either. I even cleaned the MAF, and that seemed to make the problem worse. But the weird thing is, every time I reset my ECU overnight, the car will run just for for about a week, then the problem will reoccur. So do you think the problem is my ECU? I've been battling this problem for a long time now. And I really don't want to buy a new MAF. Any suggestions? Thanks guys..

Tanner

Kilgore Trout · Nov 9, 2006

99% likely its the IAC

the98stang · Nov 9, 2006

Kilgore Trout said:
99% likely its the IAC

My IAC is BRAND NEW. I put the old one on there becuase I thought it was the problem.

However, the new IAC is not a Motorcraft. I got it from Autozone...

Kilgore Trout · Nov 9, 2006

Low freon will cause this behavior if the compressor is running when it happens...

The compressor runs in all positions except the ones immediately to the left and right of off.

the98stang · Nov 9, 2006

Kilgore Trout said:
Low freon will cause this behavior if the compressor is running when it happens...

The compressor runs in all positions except the ones immediately to the left and right of off.

It's not low freon because 1) the AC isn't on and 2) the air blows ice cold

sgarlic · Nov 10, 2006

What happens if you unload the tune? Does it have smooth idle then?

the98stang · Nov 10, 2006

sgarlic said:
What happens if you unload the tune? Does it have smooth idle then?

actually I think it runs better WITH the tune

I turned on my AC and the idle goes crazy. But my car will still do it without the AC on. It's weird..I reset the ECU, and the car runs perfect for about a week. Then the problem comes back. I don't get it...

stangGT97 · Nov 10, 2006

the98stang said:
It's weird..I reset the ECU, and the car runs perfect for about a week. Then the problem comes back. I don't get it...

Subscribing, my car does the same exact thing. Runs strong after resetting the computer, then gradually starts to run like crap

LA stang · Nov 10, 2006

have u replaced the o2 sensors?

HoustonGT · Nov 10, 2006

Replace the Autozone IAC with an original Motorcraft. I think that should fix your problem

the98stang · Nov 10, 2006

LA stang said:
have u replaced the o2 sensors?

I have not replaced the o2 sensors. But if they were bad, the car would throw a code.

the98stang · Nov 10, 2006

stangGT97 said:
Subscribing, my car does the same exact thing. Runs strong after resetting the computer, then gradually starts to run like crap

Maybe my ECU needs to be reprogrammed by a dealer? Or maybe it's defective?

Yellow2002GT · Nov 10, 2006

My Idle has been crap and found out there was a leak between the lower manifold and the Plenum....I will seal it with RTV tomorrow.....you can hear the hiss!

"ED"

the98stang · Nov 11, 2006

any other ideas?

NO BRAKES · Nov 11, 2006

possibly??

there are millions of mustangs out there, you are bound to have at least one friend that has one... try swapping ecu's. I had an idle problem with my fox a while back and I swapped my ecu with my dads. and sum bich if that was it all after i swapped the tps, iac,and the maf. im just a noob.. but maybe that will help ya?

GTCharles · Nov 12, 2006

I have an 01 GT and mine used to do the same thing so I took it to a dealership and they called it a rolling idle. They said that ford had a new pcm reprogram to solve it, so I took my car home pulled my tune out and took it back. They reprogramed it and then I reinstalled my tune and it solved the problem. I dont know if thats your problem or not but I think the pcm has an ?80,000? mile factory warrenty on it and it cant hurt to ask if there is an updated program for your car. Because they reprogramed mine for free because the pcm was still under warrenty and free is a very good price.

the98stang · Nov 12, 2006

GTCharles said:
I have an 01 GT and mine used to do the same thing so I took it to a dealership and they called it a rolling idle. They said that ford had a new pcm reprogram to solve it, so I took my car home pulled my tune out and took it back. They reprogramed it and then I reinstalled my tune and it solved the problem. I dont know if thats your problem or not but I think the pcm has an ?80,000? mile factory warrenty on it and it cant hurt to ask if there is an updated program for your car. Because they reprogramed mine for free because the pcm was still under warrenty and free is a very good price.

That is an interesting idea. However, my car was purchased from a private owner so I don't have any warrenty of any kind. But my car has about 70k miles. Maybe I'll call and see what they can do for me..

GTCharles · Nov 12, 2006

Yeah it dosent matter were you buy the car a factory warrenty is good at any ford dealership.

SilverBullet00 · Nov 13, 2006

A couple things-

a) Tons of people have these symptoms and tons of people replace their IAC. Seems like this never works! (even though all signs point to the IAC)

b) Do you need to reflash the PCM at the dealership if you have an aftermarket tune?

the98stang · Nov 13, 2006

SilverBullet00 said:
A couple things-

a) Tons of people have these symptoms and tons of people replace their IAC. Seems like this never works! (even though all signs point to the IAC)

b) Do you need to reflash the PCM at the dealership if you have an aftermarket tune?

Thats the thing...I DID replaced the IAC, and it didn't work. BUT it could have been because it was not the Motorcraft IAC. I am not sure...

If the dealer wont rape me to reprogram/update the ECU, I'll do it.

problems with the car...crap idle

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