Rough Idle ( I searched )

[EagleStroker]

Issue: rough idle, idle RPM will jump to 3k RPM, fall to 500, and continue to drop until it completely chokes the car out. Normal idle is 8-900. This started out of the blue, one day car was fine next it wasn't.

Attempts at fixing it:

1) checked, no vacuum leaks that I can find.

2) thought it possible to be the throttle positioning switch due to no pedal response. Checked and pedal was showing voltage without the throttle depressed. Replaced, throttle response is fixed but idle has not.

3) MAF. This was the first thing I checked. Unplugging cause no difference. After replacing the pedal it would smooth out the idle. Replaced, no effect on idle.

4) No code at all is tripped while this is occurring.

5) Just replaced fuel filter.

Usually at this point I would tow it to my shop. The shop that tuned my car no longer takes in work and it's left me uneasy dropping a problem off at someone elses doorstep.

 

[stkjock]

did you try to reload the tune?

 

[EagleStroker]

did you try to reload the tune?

I thought of this to, I have 3 tunes. None of which effected the problem in any way.

 

[stkjock]

you also tried to disconnect the battery for 10 mins or so?

just trying the more simple ideas first

 

[sethah]

We have a silverado where i work that was doing the same thing. Rough idle and no codes. Ended up being #1 spark plug had a crack n it. So u might check the plugs on ur car.

Sent from my SAMSUNG-SGH-I897 using Tapatalk 2

 

[EagleStroker]

Battery has been disconnected overnight.

 

[stkjock]

other things that come to mind:

TPS - have you checked the connector and the voltage?
Stepper motor on the TB could be shot


have you been able to drive it at all?

 

[EagleStroker]

I rolled it from my neighbors house where I keep it to mine. It's pretty much not drivable. I have not checked the TPS yet I was hoping I wouldn't have to replace it as much as that FRPP unit cost!

 

[stkjock]

The TPS is fairly cheap $65

http://tousleyfordparts.com/parts/2...D&model=MUSTANG&submodel=GT&vehicleid=1441222

 

[JeremyH]

Clean the throttle body and maf. This is likely the issue and should be some of the first things you do imho, even if they dont look dirty clean the maf with maf cleaner and tb with carb/choke cleaner.

Then move on to things like tune, tps, pedal, vac leaks etc.

 

[balls8302]

^ what he said

 

[EagleStroker]

Wasn't the throttle body sticking. Cleaned it well last night, when I ran a BBK I had that problem a lot. It's not MAF as there is a new sensor on the car. I'll return it once I diagnose the issue. I'll check TPS this evening.

 

[Mustang30212]

Subbing.

RH

 

[S197gt07]

Front O2's good?

Just tossing another idea out there.

 

[300angryhorses]

is it rough from start-up or does it occur after the car has warmed up? how rough is rough?

 

[Black_GT]

I say somehow try another TB on your car...Just to eliminate the TB possiblilty. I had a similar problem a few months back where my car could not keep idle (car would die at red lights or full turns). I bought a used TB off eBay ($20 shipped!!!) and that solved my problem. Idles perfectly now. guess something went faulty on my original TB.