Idle Surge @ 1500 - 2000 RPM (01 VQ30)
 

My engine has a surging idle in the range between 1500 - 2000 RPMs, only while in park (no load). Previously, it was not causing any other erratic behavior (related to the surge). However, while fixing a P0505 (Idle Air System), they adjusted the TPS settings (and idle screw, due to a high idle condition I had been fighting but finally resolved) and since then, there's 2 other symptoms:

1) When I take off slowly from a stop, once it reaches 1500 RPM, the revs jump up (as if the car went into neutral), but quickly settles in as soon as it reaches past 2000 RPM.
2) When slowly decelerating (around the same RPM range), it occasionally slams into low gear.

I suspect 1) and 2) above might be due to the TPS being improperly adjusted. However, the surging was there previously and remains the same (I first noticed it when I replaced the IACV unit, which coincided with the high idle condition which has now been solved).

My guess would be a bad TPS, but I have had 3 different shops check it (one of them being the Nissan dealership - then agin, they recommended replacing the ECU to resolve the high idle condition) and all 3 assured me the TPS is good.

The last mechanic who adjusted the TPS simply told me to keep driving it and it should self resolve (I almost laughed in his face, but who knows... it that possible?) I have previously reset the ECU numerous times with no change in this condition.

What's your thoughts?

i have simular issues as the surging idol in the same rpm range that tends to go away once warm, i have also read other posts on here whom have the same issue.. but no resolved posts as of yet, i recently had my timing advanced 2 degrees and my fuel maps reprogramed(?) , replaced tps, im gaskets,maf etc.. it has cleared up since the fuel maps were reprogamed..but its also warmed up outside where i am so im not sure if that actually resolved the issue. let me know if u find a solution as i will let you know as well. is urs specific to cold/hot engine?

you have to do the idle re-learn at the dealership

To update... I had a suspicion that adjusting the idle set screw would fix it, because after he cleaned the throttle body, there was no gap between the throttle plate and the intake runner. One of the shops he took it to did adjust it, buuut... they also adjusted his tps wrong. It did bring the idle down, but ran crappy. Soooo.... a little while ago, I re-adjusted the tps, re-did the idle relearn, and voila! I think we got it pretty close! :)

If you're not sure, always do the idle relearn before you start changing stuff, just to be sure. It always works!

^ Like he said. So those of you dealing the this surging/ idle bouncing issue, make sure to check both your idle screw and TPS settings. Follow up with the idle relearn procedure.

There's another procedure: Start car, rev to 1500 RPM (do not let it reach 2000 RPM). Hold for a minute, shut off. Repeat procedure again. I think this is for the ECU adjustment.

no you dont have to do it at the dealership. do it yourself to save money.

I have the exact same problem except mine begins to idle at 1500 after warmup .... lucky the max is stored for the summer so I don't have to deal with it until november.

I did recently adjust the throttle cable slack....