Weird idle only in park or neutral + P0171 [SOLVED - tear in intake hose]

[L36]

So I have a 07 m35x. Weird thing occurs where the car idles slightly weird when in park or neutral. The rpms drop slightly and get back to normal regardless if cold or hot. While in reverse or drive idles smoothly.
Any suggestions where to look? No CELs, 84k miles.

[veery]

And this keeps happening? Or just once? Turn all accessories off. Still happens?

[L36]

Yeah keeps happening. I just bough this car so first I'm going to check the voltage from the alternator and fill the tank with 93. I'm thinking its something with the electrical or beltdrive system.

[veery]

Describe the cycle. You start the car. It's in park. How long before it slows down. How long does it stay slow. How long does it stay faster once it switches back.
Fuel, alternator; both work the same in park, neutral, in gear.

[L36]

Its entirely random. It can start just right after starting or occur sometime after it runs for a bit. Mostly the occurrence is random. The slowing down is not significant, were talking 200rpm drop and back to normal idle, rinse and repeat. Sometimes it does one dip and does not occur for some time, sometimes it goes back to back. In neutral it happens but not as frequently when in park. Only reason i bring the alternator is because Ive seen similar issue due to faulty alternator clutch. In park and neutral the engine is getting less fuel and once you put the car in gear the fuel to air ratio gets richer thus the engine has bit more power so it does not bog down as it would in park. I'm going to fill the car up with 93 tomorrow and throw a can of seafoam into the tank and see if the issue improves.

[svard75]

Any sort of variances in idling usually points to a vacuum leak of the intake or a bad MAF sensor. Check the intake piping ensure its secure. Then check all vacuum hoses running from the plenum to brakes, pcv valve and the tube from the drivers valve cover to the intake. Lastly check the torque of the bolts of the plenum itself. You can spray some soapy water around the plenum.

[L36]

I plan to do full service on the car this week and I also discovered there is a pending recall on the gas pedal for this specific car. Overall I will post my progress in this thread considering this is a really weird issue. I expected a CEL being thrown but there are none, not even pending ones. Out of many Nissans I owned in my life this one baffles me the most.
Though i would like additional input if anyone has any.

[lovemycarM35]

try cleaning the throttle body first

[L36]

Yeah well I was told not to mess with the TB at all.

[lovemycarM35]

have the dealer do it..

[L36]

have the dealer do it..

Thanks but no thanks. If I'd like to give money away then I'd rather donate it to a cause not some guy telling me I also need a muffler bearing.

[The Bodyguard]

Maybe it had some modifications before you bought it.... try the idle re learn process (search top right of the page) If that doesn't do it you can disconnect the battery for at least 24hrs so the car can re learn idle after you re connect the battery! Usually happens after cleaning throttle body so maybe it had that service done before you bought it...

[L36]

Progress. There is a pending code for p0171 but for some reason it won't trigger into a CEL. Interesting as there is a hiss on passenger side of the engine, sounds like a vaccum leak to me. Why is it not causing funky idle in gear though? Too small of a leak?

[fat3oy]

Maybe it had some modifications before you bought it.... try the idle re learn process (search top right of the page) If that doesn't do it you can disconnect the battery for at least 24hrs so the car can re learn idle after you re connect the battery! Usually happens after cleaning throttle body so maybe it had that service done before you bought it...

^ THIS

I almost guarantee that this car had an intake. DO THE IDLE RELEARN!!!! It will fix it...

If it was not modified - I am sure that whoever had the car before dogged it shortly after a dead battery - causing wonkiness with the idle...

anyhow - idle relearn 100%

[fat3oy]

dont mess with the throttle body. lol.

[L36]

Ill do the idle relearn but I doubt mods are an issue. The car was owned by an old man who had everything serviced at the dealer.

[fat3oy]

Ill do the idle relearn but I doubt mods are an issue. The car was owned by an old man who had everything serviced at the dealer.

then dealership drove like jackasses after a dead battery... and I know plenty of old men that do stuff like this,

[L36]

Figured it out. The rubber portion that is between the MAF sensor and the PVC collector had a tear on the bottom where i did not see it. Some superglue and its like new and the car idles great now.

[Ilya]

Yep, a leak will do that.