07 4.0L - low idle problem when warm
 

I have a problem with my 2007 Mustang 4.0L, currently has 106000km and it has this rough idle feel coming from the center stack, I've done everything i can with the exhaust stuff, but trust me this isn't anything to do with the exhaust, i notice that if i leave it in Neutral or Park the rpm stays solid at 750rpm. At 750rpm i don't feel any of this rough idle or rattle feel. Once i drop it in Drive or Reverse 'once its warmed up fully' the idle is kind of low around 550-650rpm, at this idle rpm it kind of rattles and makes it feel rough. When warming up from COLD it idles pretty smooth in Drive & Reverse gears.

- Changed the sparkplugs with ngk iridium ix
- taylor street thunder wires
- only ran amsoil 5w30 & amsoil oil filters
- wix fuel filters (changed it twice in the span of 6000km)
- wix air filter (changed recently)
- lots of fuel injector cleaners used (seafoam/marvel mystery oil/lubromoly jectron/gumout) on various tanks starting at 101000km-106000km, ranging from half tank/quarter tank/near empty/full tank treatments on various tanks fills...still no help or cure.
- seafoam spray (induction cleaning through t/b)
- cleaned the throttle body/plate already
- cleaned the maf thoroughly with crc cleaner (not even one piece of dust or grime on it)
- NO ENGINE LIGHT or CODES when scanned

Check these pics to understand

The pic below are the rpm in Drive and Reverse (when its been driven for a while and fully warmed up) stays around 550-650rpm and rumbles the automatic shifter area and floor.

Another thing i noticed is when the cooling fan is on, it gets worse, it dips down as low as 500rpm and catches back to 650ish and it does this about 4 times to 500rpm before the fan stops and then computer resets it to 700-750rpm and it smooths out and it drops back and feels unstable around 550-650 (hope it makes sense) maybe stock motorcraft battery weak?

http://imageshack.us/a/img854/9269/qzf5.jpg

This pic is in Park and Neutral (when its driven for a while and fully warmed up) stays solid at 750rpm and smooth like a rock.

http://imageshack.us/a/img546/8923/s213.jpg


Any help will be appreciated!!! :D
Thank you.

if you have a tune or plan on getting one that will fix your problem because you can set the drive, neutral and park idle settings

Thanks for the reply, i was talking to a bama representative and he recommended the sct/sf3/x3 tuner and that they can set the idles for each gear. I'm gonna consider a CAI & tuner from AM. I hope it stops after having it tuned.

How's your stock airfilter? Have you had your battery and alternator tested?

My battery is good, holds 75% charge atleast during storage, i throw on my schumacher battery charger once ina while to bring it back to 100%

I've dropped a bottle of amsoil P.I improver (one bottle a tank per month) for 3 months straight with no cure.

Air filter is mint, throttle body is clean, fuel filter is new...what can be the problem??

Car is in storage for the winter...i'm gonna take it for a spin tomorrow

Sounds like you take really good car of your car. I think this is a very common problem with these V6 cars. My question posed in another reply about rough idle: Will an aftermarket alternator that produces more amps that the stock Ford alternators handle the idle electrical loads better and not cause an engine rattle? Anyone with aftermarket alt. have the answer?

Took it for a spin yesterday and it felt alot smoother, guess the battery being charged close to 100% helps haha.

Mine has a reman alternator. Came with it on the car when i bought it! There was a silver sticker that clearly said [REMANUFACTURED] lol, i just peeled it off at the time and continued detailing the engine bay :P

I think the rattle you're talking about is the rattle when you hit the switches or when the rad fan kicks on, when it kicks out the idle smooths out and rpm is nice and high at 750rpm or something. But yes its common for these 05-09 to do this. When it happens the idle jumps down to like 600rpm for a split second and rattles the center stack/dash.

I'm starting to think it can be the upstream o2 sensors, i know my stang gives off more black ash/black soot like things in the tail pipe, maybe the o2 sensor is coated and not balancing the air/fuel properly? I know on my 04 3.4L grand am gt1, the tail pipes never gave off any dark black soot, after changing sparkplug/wires/upstream o2. Idles and runs like a bullet, its my daily winter beater that i got for $500.

Whatever it is, im not giving up easily lol, its gotta be something simple. I still get 500km to a full tank on the mustang, which is still good for having a 58L tank.

I will post up if i find a cure for this.