Irregular idle 07 mustang gt

[Michael sommers]

I got an 07 gt about 3 weeks ago, and I’m having a strange issue, the car idles pretty much perfect( maybe drops 50 rpms or so every once in a while) when sitting still, but when I’m driving and I push the clutch in, the idle will jump from 600-800, then back down to 500 in a span of about 10 seconds, then after that it will smooth out and be perfectly normal, It seems like it only happens when I’m driving and I push the clutch in or shift into Neutral, I have a bad 02 sensor after the cat, but from what I know it shouldn’t affect anything, any ideas?

 

[Bullitt95]

Clean the inside of the throttle body thoroughly. Any dirt that accumulates between the throttle blades and the bores can affect the idle quality.

 

[Michael sommers]

Clean the inside of the throttle body thoroughly. Any dirt that accumulates between the throttle blades and the bores can affect the idle quality.

Throttle body has recently been off and cleaned, it’s spotless now.

 

[manicmechanic007]

You might want to look that up and see if it is the normal strategy for your car
It sure was back in the eighties
Many had a clutch switch that when depressed would do just that
Hang the idle up to keep the car from falling on its face between shifts
I would not worry too much about it
The hotrod Mustangs are a little harder to drive without that feature

 

[Michael sommers]

You might want to look that up and see if it is the normal strategy for your car
It sure was back in the eighties
Many had a clutch switch that when depressed would do just that
Hang the idle up to keep the car from falling on its face between shifts
I would not worry too much about it
The hotrod Mustangs are a little harder to drive without that feature

It’s not a hanging idle is the thing, it’s all over the place from 5-800 rpms for about 10 seconds and then it smooths out

 

[manicmechanic007]

Maybe it is learning idle?
When is the last time you had the battery disconnected ?
Possibly cleaning the plate made it different enough (the tp voltage) to affect idle speed

 

[Michael sommers]

Maybe it is learning idle?
When is the last time you had the battery disconnected ?
Possibly cleaning the plate made it different enough (the tp voltage) to affect idle speed

I just had the battery disconnected because I had to take stuff off to fix a coolant leak I had under the intake manifold, but I’ve disconnected the battery multiple times since I got the car, and I cleaned the throttle body the 1st week I had it, it did it before I cleaned it too.

 

[manicmechanic007]

If disconnected long enough it will erase the kam memory and then it will have to relearn idle speed
That may not be your issue if it straightens itself out quickly
Any codes?

 

[Michael sommers]

If disconnected long enough it will erase the kam memory and then it will have to relearn idle speed
That may not be your issue if it straightens itself out quickly
Any codes?

I have codes for stuck Lean bank 1 sensor 2, that 02 sensor also has a code for stuck rich, and a high voltage code as well, all for that same 02 sensor

 

[manicmechanic007]

Well you better look into that
Bank one sensor two should have no effect on engine performance (it's a converter efficiency sensor)( after the cat)
However excess voltage is a problem
Can you read the pids for the (4) O2 sensors?
When you say stuck lean bank 1 makes me think of a leaking intake gasket or a warped plastic manifold

 

[Michael sommers]

Well you better look into that
Bank one sensor two should have no effect on engine performance (it's a converter efficiency sensor)( after the cat)
However excess voltage is a problem
Can you read the pids for the (4) O2 sensors?
When you say stuck lean bank 1 makes me think of a leaking intake gasket or a warped plastic manifold

I just replaced all the intake manifold gaskets and the car doesn’t seem down on power or anything no misfires at all, just the weird idle issue when coming to a stop, all the 02 sensors fluctuated between 0.1 and 0.9v, but the one that has the codes, seems to rarely read anything, just 0.0V. But that’s doesn’t make sense to me because I have a code for high voltage on that sensor. And it also confuses me how I have rich and lean codes for the same 02 sensor at the same time

 

[manicmechanic007]

Better visually inspect the wiring harness for any problems shorts etc
Corrosion used to be a problem near the battery
The corrosion would travel up the wiring a ways and cause all sorts of trouble

 

[manicmechanic007]

Trace that rear O2 sensor wiring back up thru to the processor
Replace the sensor?
How much voltage?
Used to see about 8 volts on Broncos where the power wire for the starter and the O2 sensors were wired in the same loom
Corrosion would set in and cause induced voltage in the line they call it causing the 8v on the front O2 sensors
Ran like puke cant remember the codes

 

[Michael sommers]

Trace that rear O2 sensor wiring back up thru to the processor
Replace the sensor?
How much voltage?
Used to see about 8 volts on Broncos where the power wire for the starter and the O2 sensors were wired in the same loom
Corrosion would set in and cause induced voltage in the line they call it causing the 8v on the front O2 sensors
Ran like puke cant remember the codes

The 02 I have the code for was at 0.0v most of the time then very occasionally (like once every 20-30 seconds) bump up to 0.1v

 

[manicmechanic007]

What does the other side rear sensor read?
When you first start the car and it is in open loop the front and rear sensors will read about the same
(the rear sensor will mimic the front sensor)
After approximately 2 minutes of engine operation the processor switches to closed loop where all the sensors are the input
The converter gets hot and starts working. At that point the rear hegos should read about .45v and stay there
My advice is to replace both rear hegos with Motorcraft parts (they run in stereo and if you replace just one
the computer will think the other one is switching slow and turn on the check engine light)

 

[Michael sommers]

What does the other side rear sensor read?
When you first start the car and it is in open loop the front and rear sensors will read about the same
(the rear sensor will mimic the front sensor)
After approximately 2 minutes of engine operation the processor switches to closed loop where all the sensors are the input
The converter gets hot and starts working. At that point the rear hegos should read about .45v and stay there
My advice is to replace both rear hegos with Motorcraft parts (they run in stereo and if you replace just one
the computer will think the other one is switching slow and turn on the check engine light)

If I remember correctly the other rear sensor read at .45v or very close to it, I haven’t replaced it because I didn’t think it would effect performance at all, and there was more urgent things the car needed. The catalytic converters rattle quite a bit so I’m pretty sure they are blown out and i was getting ready to replace them, I was thinking that might be my problem.

 

[manicmechanic007]

Damn straight start with the broken up cats
Then replace the rear hegos when you can
You can test the converters (or exhaust) for being plugged with a vacuum gauge
Used to put large hose clamps around the heat shields on the converters if that was all that was rattling
Sometimes the converter substrate breaks up and fills the muffler

 

[sgtpepperthestang]

I got an 07 gt about 3 weeks ago, and I’m having a strange issue, the car idles pretty much perfect( maybe drops 50 rpms or so every once in a while) when sitting still, but when I’m driving and I push the clutch in, the idle will jump from 600-800, then back down to 500 in a span of about 10 seconds, then after that it will smooth out and be perfectly normal, It seems like it only happens when I’m driving and I push the clutch in or shift into Neutral, I have a bad 02 sensor after the cat, but from what I know it shouldn’t affect anything, any ideas?

i see that you have codes but have you also checked the throttle position sensor?

 

[Michael sommers]

i see that you have codes but have you also checked the throttle position sensor?

I have not checked the TPS, how do you go about testing it?

 

[Michael sommers]

Damn straight start with the broken up cats
Then replace the rear hegos when you can
You can test the converters (or exhaust) for being plugged with a vacuum gauge
Used to put large hose clamps around the heat shields on the converters if that was all that was rattling
Sometimes the converter substrate breaks up and fills the muffler

I was hoping it was the heat shields, but I’m really not sure, seems to come and go, sometimes it rattles at certain rpms, other times it doesn’t, it also will rattle when I pound on it with my fist, but there is also other times where I can’t get it to rattle at all. Maybe I’ll give the hose clamp trick a shot