Surging/Hunting Idle Help

[Toasty]

I have the Z24i engine in my Pathfinder but that shouldn't make much of a difference, they use the same emissions and tbi components as the VG30.

 

 

It runs like a champ though and can cruise at 80mph on the highway, the problem is that the idle surges pretty bad when the engine is warm. The cold idle seems a little high but it's hard to tell since my Pathy doesn't have a tach... When it's warm the idle lowers by a few hundred RPM and then once it's hot, it will surge between low and high idle every 5-10 seconds. I went through sprayed all the vacuum lines with brake cleaner and it didn't change a thing, neither did pinching vaccum lines. I replaced some of the lines under the air cleaner that had nearly rotted off their nipples but it didn't do much.

 

This is super weird. There are three small vacuum lines that attach to the air cleaner, two come off the intake manifold, one goes to the air temp sensor and the second lines feeds the hot air vacuum motor, the third goes is a non vacuum line that goes to the end of the EGR solenoid. The engine was surging, but when I removed the line that feeds the vacuum motor (via the temp sensor in the air cleaner) the idle settled down to normal.

 

I figured that was it and replaced those lines. Afterwards the idle kept surging even if I disconnected the line again. The hot air vacuum motor works fine and doesn't change the warm idle with it up or down. The hot air hose IS loose on the bottom (didn't have a hose clamp handy) but it's just feeding hot air coming off the exhaust manifold anyway, so not air tight...

 

Now I have checked the ECU. It gave me code #11 which the ECU guide says in the manual transmission model shows up sometimes even though the crank position sensor is fine. The other code was #13 for the engine coolant temp sensor. I unplugged the connector and it idled smoother (albeit high) even when hot, when I would plug in the connector it would lower the idle again and start surging. I went to the parts store and replaced it but there is still no change.

 

I'm not sure what else to look at. I don't think the crank sensor on the distributor is bad because it drives fine aside from the funky idle. The rest of the vacuum lines seem to be in good shape and spraying/pinching them didn't do anything. The wax type fast idle thing looks pretty crusty but it seems to be working the plunger (can see a clean shiny part of the shaft). It may not be set correctly though, I started running out of daylight.

 

Any ideas?

 

[Kingman]

I would recommend cleaning the MAF and plug pins, and making sure there is no air in the coolant lines going to the wax cold idle valve. Also make sure the air cleaner is tight on top of the throttle body and there's no leak there.

[Toasty]

I'll clean the MAF this weekend and see if that helps, plus check the connection. The air cleaner is tight but I'll take a closer look at that. For the idle control valve, I'm guessing I just burp it?

[Toasty]

I fixed it btw, the thermo wax module thing was way out of adjustment. I'll probably need a new one in the future but it works now. I also had a problem with the idle being super rough when it got warm. I had the first and second vacuum lines swapped on the air cleaner distribution tree, whoops.