Idle problems (these seem popular lately)

[Sifujon]

Idle is bumpy, moves up and down, misses all while under 1000 rpm. The codes that have come up are P0171 (Fuel lean bank 1), P0325 (knock sensor), and P0400 (Exhaust gas recirculation flow malfunction).

The truck has new plugs, wires, rotor and cap, fuel pump and filter, and I just installed a new MAF (which helped a lot), and a new air filter. I pulled the live data using the OBDII reader and it looks like this:

FUELSYS1 CL
FUELSYS2 CL
LOAD_PCT(%) 19.6
ECT(C) 85
SHRTFT1(%) 21.9
LONGFT1(%) 9.4
SHRTFT2 7.8
LONGFT2 9.4
MAP(KPA) 45
RPM 712
VSS 0
SPARKADV 19
IAT(C) 46
MAF(G/S) 4.52
TP(%) 0
O2SLOC B1S12--B2S12
O2B1S1(V) 0.00 G
SHRTFTB1S1(%) 6.3
O2B1S2 0.00
SHRTFTB1S1 N/A
O2B2S1 0.00
SHRTFTB2S1 14.1
O2B2S2 0.01
SHRTFTB2S2 99.2 G

I'm just a novice so I hope that info can help someone with more experience diagnose my issue. The o2 sensor readings look wonky to me, other than that not sure. The EGR code being thrown has been there a while, I don't think it's the (main) culprit. Any thoughts would be appreciated!

[Rockwood]

Okay, here's what I think - Bank 1 (passenger side) has a short term fuel trim of 21.9 percent rich, while bank 2 has a 7.8 percent rich reading. That means that the system is trying to compensate for too much air - a vacuum leak - on bank 1. Ignore the knock sensor for now, I think it will probably go away when you fix your main issue.

The system is giving you p0171 because of the vacuum leak as well. The p0400 is the Exhaust Gas Recirculation system, so I would guess something in the EGR system is causing your vacuum leak - it also has a couple of vacuum solenoid valve switches in it.

Start by going thru the EGR system and hoses looking for vacuum leaks. Check your other vacuum hoses for leaks as well. Search for 1997 Pathfinder EGR valve on Ebay, you will get pics of the valve, and pics of the vacuum solenoid valves will come up as well. That way you know what parts you are looking at.

Pretty sure because of the P0400 you have a problem to find with the EGR system - once you cure the vacuum leak I think the idle should smooth out.

[Sifujon]

Thanks! That sounds like a solid plan, I'll take a look today and see if I can't find what the issue is. I'll update the thread with what I find.

[Sifujon]

Ok so major reverse progress; the truck will barely run for a few seconds now, and it's throwing a P0300 code as well. Last couple days I've lost all pickup and the check engine light occasionally blinks. I've checked the vacuum hoses and don't feel any leaks. I can't do the normal test with the car running, as it won't run. Plug wires seem tight, nothing has got wet recently. I'm told I have a brutal vacuum leak but I don't see one, and I'm unsure how to even verify that without a running vehicle. I'd also hate to just start replacing parts - starting with EGR - in case that's not the actual problem. Any help would be massively appreciated!

[Sifujon]

Just took some of it apart to see. There was a vacuum hose off the bottom of the TB, from the Egr solenoid. Also checked to see if the EGR worked with vacuum, it does. Buttoned it back up, and it still barely runs. Seems like no change at all. Stalled and it ran a P0325 code. Still confused, back at it tomorrow.

[Sifujon]

The EGR system seems to run fine, I did the tests in the shop manual and it seems to open up after 2000 rpm like it's supposed to. I've checked all the lines physically and re-tightened some things. Checked the TB and TPS seals as well, all good. I also tried disconnecting the large vacuum lines from the intake, and plugged them up to see if the idle would sort itself out with the problems gone, no change. The symptoms still seem like vacuum leak but I can't find any.

Now I'm wondering if there's an issue with the intake? Plus now I'm super confused about the EGR code it's been throwing for the last couple years.....completely stumped at this point. Might have to burn it down and just get the insurance /s

[Sifujon]

Nobody's reading this but I'll just keep updating in case it helps someone in the future. I pulled a distributor from a wrecker and installed it yesterday, and it made no difference whatsoever. My next bet is either trying O2 sensors from that wrecker (just to see if it's a difference, I'd get new), or maybe checking out the Idle Air Control Valve. The IAC is an absolute b**** to get to so it'll be second. The vehicle is still barely running and we went through the entire EGR system and found no major issues. The live data doesn't give any great info, other than it saying the short and long term fuel trims are still very high; +7-25%. No clue why that is.

[Blindaviator]

If you can get it to run and / or idle you can spray carb cleaner around all the vacuum hoses to see if there are leaks... If you spray a hose and the engine speeds up you have a leak...

And I agree the fuel trim running high means it is trying to compensate for too much air... Try disconnecting different sensors and see if it does / doesn't change the problem... If it gets worse then that sensor is likely working...

Have you checked the hoses on the bottom side of the lower intake that goes to the passenger side PCV Valve and the PCV valve its self??? The hose is on the bottom side of the lower intake at the rear of the engine and the PCV valve is on the passenger side just under the edge of the intake in the valve cover (both are VERY tough to see or reach without taking off the intake)... There are 2 rubber hoses between the PCV and the intake, one goes from the PCV to a metal tube and the other goes from the other end of the metal tube to the bottom side of the intake...

Also check the hose on the front of the intake that connects the 2 valve covers together (although that one doesn't connect to vacuum)... When I replaced my water control valve recently all of those hoses were hard and starting to crack...

If you decide to take the intake apart to reach the hoses I suggest you replace the water control valve while you are in there since it is so difficult to reach... It is basically a thermostat and over time they wear out...

[QCtech]

Your problem might be you IACV. It is not that difficult to take out. At least on mine which is a 2003 and its a little different. If you have not taken it out, I bet is clogged. When I cleaned mine and connected it back, it first threw me all kind of codes, and after I erased them they never came back. Your heavy leak could be the IACV gasket, so get a new one. Mine was so clogged that you could not see light coming from the other side. Also troubleshooting and cleaning your injectors might have a lot to do. Best of luck.

[Buzzman]

Nobody's reading this but I'll just keep updating in case it helps someone in the future.

Well, I for one keep reading the posts, although I am not on here every day.
Most of the Pathfinder members here seem to have the newer models with the 3.5 engine (2001 and newer).
The 3.3 vs 3.5 engine is night and day. Not even close.
I know next to nothing about your engine, so I can't really help you, as much as I'd like to.
I'm going to assume there is an IACV in there somewhere, so I'd be tempted to clean that out, or replace it.

[Niti QX4]

Any updates?