Idle Drops Too Much

[mdmellott]

Other than the IACV, what else effects the idle while not moving forward. At a stand still, in neutral or park and with the brake depressed or not, my idle remains at a solid 750rpm with absolutely no variation. As normal, when I put it in drive with the brake depressed, the rpm will drop to 650 and the engine will still be running smooth and normal. However, most of the time, I can watch the tach and see it suddenly drop from 650 to 550 in an instant and hear the engine stumble a bit, so to speak, like a switch just got flicked. As soon as I start rolling when I shift to drive or reverse, without even depressing the accelerator pedal, my rpm goes back up to around 700. My IACV is brand new and this annoyance has been happening even before I replaced it. My throttle body is clean as a whistle as is my MAF sensor, which is also relatively new. Is there some other component, switch or sensor that could be a bit flakey that would cause this? There is never a DTC flagged when this sudden drop happens and I see no other performance issue while driving. I can continue to ignore this and be ignorant about it but I know something's not quite right. Any ideas? Gremlins? I have read through numerous posts about this but found nothing I haven't already checked to remedy this minor glitch. I'm betting it's user error yet I'm hoping there is something someone can suggest that I haven't already tried.

[VStar650CL]

I presume you've already tried re-matching the MAF and ECM with an IAVL? If so, the best thing is to put a streaming scanner on it and see what changes when the behavior happens. Sometimes aged A/F sensors can cause the ECM to load up fuel and then over-react, that will show up in both the A/F-alpha (STFT) and injector pulse width. A very tiny vacuum leak can cause the same sort of transient over-correction, but the STFT will usually show that too -- a hair high at idle, then normalizing when the RPM's rise. You might also want to see if your ECM firmware is the most current version. Nissan has a general tendency to make the A/F maps in the ECM more stringent than they need to be, then loosen them up over time. That tends to be a problem with new or revised models, and your '02 was a major revision from the '01's. You might be driving around with dinosaur-ware and not know it.

[mdmellott]

The IAVL has been done and redone just to be sure. No A/F sensors on my '02, just the four HO2 sensors. Still, that is a good idea regarding the streaming scanner. The graphing function on mine shows a more responsive indication to real time live changes than just the numerical data screen. It's kind of a cheap scanner but it has a few good features. I do still have a few very old original vacuum hoses installed. If there's a small leak I'll find it. I never considered the ECM firmware. I have no idea about the firmware version currently loaded since I bought my '02 in 2012. Those were all great tips for me to go on. I'll see what I can find out this weekend.

[mdmellott]

I rarely drink alcohol, but when I do, I prefer it neat. A watered down Marker's Mark has a terrible taste. My Pathfinder prefers its alcohol neat as well. I tested, monitored, retested, and inspected every possible cause to the minor headache my Pathfinder has had for the past several years and just happened to stumble upon the cause. I'm not drinking enough. I have kept my tank topped off over the past few years whenever my glass was half empty because I don't drive it as much as I once did and I didn't want the bare metal in a half empty tank to rust just sitting around. The 10% ethanol I am forced to consume in the gas I buy is very hygroscopic so it sucks up a lot moisture from the air. It also degrades faster than straight gasoline because of its higher evaporation rate so phase separation from the fuel happens quicker than I consume it, which lowers the otherwise higher octane fuel mix I normally purchase and drops out the separated water to the bottom of my tank. I can't remember when I last let my tank get down to the point where my low fuel warning light came on but I just did that yesterday. After I filled up my tank, my headache went away. It's a "hair of the dog" sort of thing. Bottom line: Drink more alcohol but do it responsibly and never pour whiskey over ice unless you drink it before the ice melts too much.

[VStar650CL]

Bottom line: Drink more alcohol but do it responsibly and never pour whiskey over ice unless you drink it before the ice melts too much.

There's my giggle for day. Love it!