1999 Pathfinder rough idle

[Jables]

Okay, so first off, I didn't write an introduction because I'm just kinda on here for a friend who bought a 99 Pathfinder. I drive a Jeep, but he was looking into offroading with me and he didn't want to buy a Jeep. So he went out and found this beat up Pathfinder. It was throwing 2 codes to begin with, one code dealing with an o2 sensor and the other dealing with the mass airflow sensor. We've since then changed the o2 sensor and cleaned the mass airflow sensor and have removed the codes. The codes have not come back on and we've been driving it around quite a bit to see if anything throws out more codes.

 

As of right now, it is not throwing any codes. When it starts cold, it runs perfect. No miss, no rough idle. Get it warmed up, and BLAM. Runs like a turd and stalls at stops. I've checked the grounds I can see, spark plugs are brand new, we threw in a new fuel filter and have ran seafoam through it. This is definitely not something I'm used to working on and nothing that has worked for me is working for my friend. Some people have suggested the coolant temp sensor is busted, but I'm pretty sure that would throw a code?

 

Please help this poor soul. I want to see this thing run good, it's not a bad vehicle at all. Thanks in advance.

[01Pathmaker]

Coolant temp sensor generally won't throw a code oddly enough. Was this happening before cleaning the MAF sensor? If not, check to be sure there are no leaks in the intake hose between the sensor and throttle body. Also be sure all vacuum lines in the area are properly connected and in good shape. A vacuum leak in that area could cause this issue. Be sure to check the rubber elbow that connects to the throttle body real well, cleaned my MAF as routine maintenance and ended up with a hairline split in that elbow giving me stumbling and hesitation, took me a while to pin that one down. If all looks good then look into the CTS,as that would be the next likely culprit.

[Kingman]

Yes, the temp sensor doesn't usually throw a code until it fails open. Out of range is still functioning so the ECU doesn't know any better. Ohming it out when cold and hot and comparing to the FSM, along with ohming the harness back is a good idea. There is also an issue with the MAF ground, and there is a new OEM harness you can buy to fix it or fix it yourself. As was said, any leaks after the MAF will cause issues. Distributors are known to cause the issue as well but for the most part they just up and quit for a while.

Edited August 12, 2015 by Kingman

[tmoore4512]

Agree fully with the previous two posts.

I would suggest that you follow the two large lines that come out of the intake piping between the MAF and the throttle body. One goes to a hard line that routes around to the PCV on the passenger side valve cover the other goes back through a second hard line that goes into the motor to feed the PCV system.

While looking at your truck with the hood up standing in front of the motor, facing it...look at the hard lines. One comes straight towards you, the other goes to the driver side. Both have an intermediate rubber hose that connects them to the intake piping using Nissan's favorite clamps. Those jokers WILL CRACK.

The one that comes straight out towards you, parallel with the motor is the one you need to seriously check. Its strange because when disconnected the motor will not run at all. When connected with a minor leak it runs like you described. When connected properly it runs perfect.

Just my .02

[Precise1]

Yes, the temp sensor doesn't usually throw a code until it fails open. Out of range is still functioning so the ECU doesn't know any better. Ohming it out when cold and hot and comparing to the FSM, along with ohming the harness back is a good idea. There is also an issue with the MAF ground, and there is a new OEM harness you can buy to fix it or fix it yourself. As was said, any leaks after the MAF will cause issues. Distributors are known to cause the issue as well but for the most part they just up and quit for a while.

Yes, the first thing I would do. The FSM is available for free download in the pinned thread in the Garage section.

We disturbed the connector for the temp sensor on a friend's WD21 (same system). It was idling/warming up and then flat died and wouldn't start until we took the connector apart and cleaned it; runs fine since. Might want to give it a wiggle when it is running to see if there is any effect.

 

Vacuum leaks would be #2, but I suspect if you had one bad enough to stall it out, you'd know...

 

B