Low Idle after rev up

[Ross]

The car runs great but after you rev it in nuetral the idle drops and then jumps back to normal. The car has a plenum spacer on it.

 

[stkjock]

mods other than the spacer?

why do you have the spacer?

 

[Ross]

The only other thing on there is a flowmaster exhaust. I did not put the spacer on there I know that they are a waste of money the guy that had the car before me did.

 

[redfirepearlgt]

Pull the useless thing off and see if that changes anything. May have to give adaptive learning a chance to relearn what has been undone. There will occasionally be a dip on decel even on a stock idle. It should not be very significant however. Finding the perfect balance in every ambient and atmospheric air condition is next to impossible.

You may wish to remove the MAF and clean it and see if that helps some. Proper metering of air is even more critical down low where the PWM of the fuel injector is at its shortest and a little correction goes a long way. Idle is the most difficult of any tuning process though people often think its the other way around. It is a serious balancing act and something as simple as turning on an AC unit or kicking on of an electric cooling fan can effect it.

Make sure if you remove the MAF that you install it the same way it came out. Also make sure if you clean it you use MAF cleaner and NOT TB cleaner in case you aren't aware. TB cleaner will damage the element in the MAF. Also make sure it has had time to dry out before plugging it back in. The TB could also need to be cleaned as well. These things will effect idle as well as overall drive ability. Make sure your air filter is clean as well (you can see through it if you hold it up to light).

Best thing to remember if you don't wrench much (sorry if talking down to you if you do wrench a lot) is to undo only one thing at a time. Then see how that effects things. IF you do 2-3 things at once and then things get worse you have no idea where to begin to get it back to where it was.

Good luck. And welcome to the site.

 

[46addict]

You may wish to remove the MAF and clean it and see if that helps some. Proper metering of air is even more critical down low where the PWM of the fuel injector is at its shortest and a little correction goes a long way. Idle is the most difficult of any tuning process though people often think its the other way around. It is a serious balancing act and something as simple as turning on an AC unit or kicking on of an electric cooling fan can effect it.

When cleaning the MAF, does the MAF body need to be taken apart? Or is it just a matter of spraying cleaner on it and letting it dry?

 

[sman247]

just spray the cleaner and let dry, dries almost immediately. just make sure you use MAF sensor cleaner. I had a similar issue a while back, turned out one of the battery terminals was loose, was throwing a battery light too though. Probably not your issue but just a thought

 

[Ross]

Pull the useless thing off and see if that changes anything. May have to give adaptive learning a chance to relearn what has been undone. There will occasionally be a dip on decel even on a stock idle. It should not be very significant however. Finding the perfect balance in every ambient and atmospheric air condition is next to impossible.

You may wish to remove the MAF and clean it and see if that helps some. Proper metering of air is even more critical down low where the PWM of the fuel injector is at its shortest and a little correction goes a long way. Idle is the most difficult of any tuning process though people often think its the other way around. It is a serious balancing act and something as simple as turning on an AC unit or kicking on of an electric cooling fan can effect it.

Make sure if you remove the MAF that you install it the same way it came out. Also make sure if you clean it you use MAF cleaner and NOT TB cleaner in case you aren't aware. TB cleaner will damage the element in the MAF. Also make sure it has had time to dry out before plugging it back in. The TB could also need to be cleaned as well. These things will effect idle as well as overall drive ability. Make sure your air filter is clean as well (you can see through it if you hold it up to light).

Best thing to remember if you don't wrench much (sorry if talking down to you if you do wrench a lot) is to undo only one thing at a time. Then see how that effects things. IF you do 2-3 things at once and then things get worse you have no idea where to begin to get it back to where it was.

Good luck. And welcome to the site.

Thanks for the advice I will give it a try.


Sent from my iPhone using Tapatalk

 

[Dino Dino Bambino]

Try cleaning the inside of the throttle body between the blades and the bores. Dirt in that area can prevent the engine from inhaling the proper amount of air when the throttle is closed.

 

[Ross]

Try cleaning the inside of the throttle body between the blades and the bores. Dirt in that area can prevent the engine from inhaling the proper amount of air when the throttle is closed.

Okay will do. This is my first time owning a mustang and it also has a small shake when it idles. Is this normal for a v8?

 

[bl817]

when you take the TB off, you can move the butterfly plates, spray the cleaner inside and scrub the gunk off, your not going to hurt it. clean and reinstall. the shake is probably bad motor mounts. good luck

 

[RocketcarX]

The shake could also be an indicator of the car needing a tune up, in this case spark plugs and coil boots.

 

[Dino Dino Bambino]

Okay will do. This is my first time owning a mustang and it also has a small shake when it idles. Is this normal for a v8?

No not normal. A 4.6 3V with a stock cam should have a glass smooth idle.
Like others have said, the engine may have a small misfire and need new plugs +/- COPs. Also get rid of that waste of space TB spacer and sell it in eBay.