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Having an issue with a low / rough / vibrating idle. (550-650 RPM)
The rough idle gets much worse when put into drive or reverse.
What's even more interesting is that the idle drops even LOWER / Rough when I turn the steering wheel.
The rough idle gets even worse when I turn on the headlights -- the idle drops even lower
There are no codes ---- The car has not stalled yet, but something is definitely wrong - way too much vibration.

I have done so much to attempt to fix this issue:

1.) Changed spark plugs (NGK Ruthenium), used dielectric grease on ignition coils.
2.) Changed PCV valve
3.) Transmission fluid changed
4.) Replaced right engine torque mount
5.) Cleaned MAF sensor
6.) Cleaned Throttle body
7.) Cleaned / Replaced engine air filter (K&N)
8.) Ran Complete Fuel system cleaner - twice (Techron) - Fuel injectors, etc.

I also have recently performed the IAVL (Idle Air Valve Relearn) procedure. I cannot get this car to idle smooth. I really need some help.

Previous post was in regards to locating IACV, which I learned is not available on 5th gen Altimas
post found here:

For reference -- this is a 2013 Altima 2.5 SL, with 82,000 miles on it.

Please help!
 

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There are only a few things the ECM has to trust that won't throw codes, and most of those will affect the way the car runs above idle. Leaving out the MAF, when only the idle is rough, the most likely culprits (probably in order) are a small vacuum leak, a dirty throttle body, or carbon on the intake valves and piston crowns.

You can eliminate or verify a small vacuum leak easily with a streaming scanner. Monitor Short Term Fuel Trim (STFT). It will usually be slightly rich at idle (a few percent), but if it's very rich then a vacuum leak is possible. To verify it, run the engine up to 2000~2500 RPM while watching STFT. If it normalizes toward zero as the RPM's increase, there's a vacuum leak for sure.

Crappy Throttle Bodies are easy enough to clean, pay most attention to the back and lower edge of the butterfly. Use a toothbrush and a good quality intake cleaner. Never force the butterfly open manually, have an assistant floor the pedal and let the throttle motor open the plate.

Carbon is also pretty easy to resolve. You'll need a squirt can of ATF (any kind). Warm the car up thoroughly with the Brake Booster hose loose and your thumb over the end. Have an assistant raise the RPM to 3500~4000 and squirt a teaspoon or so of ATF down the booster hose. Hot carbon on the valves and crowns will literally be cracked to pieces by the cold film of mineral oil vapor, then the cats will consume the remnants. In the old days, small block Chevys and Fords could build up huge piles of carbon on the backs of the valves, and doing the ATF trick would send quarter-sized chunks out the tailpipe onto the garage floor. Cats prevent that on modern cars, but even though you won't see the results, your car will feel the difference.
 

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There are only a few things the ECM has to trust that won't throw codes, and most of those will affect the way the car runs above idle. Leaving out the MAF, when only the idle is rough, the most likely culprits (probably in order) are a small vacuum leak, a dirty throttle body, or carbon on the intake valves and piston crowns.

You can eliminate or verify a small vacuum leak easily with a streaming scanner. Monitor Short Term Fuel Trim (STFT). It will usually be slightly rich at idle (a few percent), but if it's very rich then a vacuum leak is possible. To verify it, run the engine up to 2000~2500 RPM while watching STFT. If it normalizes toward zero as the RPM's increase, there's a vacuum leak for sure.

Crappy Throttle Bodies are easy enough to clean, pay most attention to the back and lower edge of the butterfly. Use a toothbrush and a good quality intake cleaner. Never force the butterfly open manually, have an assistant floor the pedal and let the throttle motor open the plate.

Carbon is also pretty easy to resolve. You'll need a squirt can of ATF (any kind). Warm the car up thoroughly with the Brake Booster hose loose and your thumb over the end. Have an assistant raise the RPM to 3500~4000 and squirt a teaspoon or so of ATF down the booster hose. Hot carbon on the valves and crowns will literally be cracked to pieces by the cold film of mineral oil vapor, then the cats will consume the remnants. In the old days, small block Chevys and Fords could build up huge piles of carbon on the backs of the valves, and doing the ATF trick would send quarter-sized chunks out the tailpipe onto the garage floor. Cats prevent that on modern cars, but even though you won't see the results, your car will feel the difference.
wow.. this I never heard of.... carbon build up is common in a lot of cars.. This ATF won't damage the engine? You mentioned Brake Booster hose, is this the intake hose or vacuum line?
 

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No, it only damages the carbon. It's just mineral oil, it's harmless to cats. The only risk is that if the carbon buildup is very extreme, sometimes a huge chunk can break off and squash the electrode on a spark plug on its way out of the engine. But on a '13 with MPI it's unlikely you'd ever get that much buildup, it's much more common on direct-injected (DGI) engines. On a gen6 ('19-up) you might need to worry about that.

I meant the vacuum line, pop it loose from the booster and cap it with your thumb till you're ready to squirt the ATF.
 
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