Intermittent surging at low speed - faulty NSS?

[dionphaneuf]

I haven't been driving my 500E much recently, in part because I haven't needed to but also because it has an annoying 'surging' at low speeds - every two or three seconds it will slightly lurch forward, then lurch back, then forward, etc. It happens below 15 MPH or so, which makes city driving annoying. If you put it in neutral it totally goes away, so I find myself almost 'downshifting' to N as I approach a stoplight. Above 15MPH (constant speed, highways, whatever) you can't tell this issue at all.

About 2-3 years ago I swapped my OE NSS for a new one as I was trouble shooting another issue (the original NSS was fine). I'm 99% sure I saw a post of someone describing this exact issue I'm having, and tracing it to a faulty 'new production' NSS in the last 2-3 years, but I can't for the life of me find that post. I've searched a few times and can't seem to locate it. I'd love to be fairly certain this will solve this issue, as replacing the NSS is a bit of a PITA given the space available, so if anyone remembers or can recall I'd really appreciate it. I know this isn't really a symptom of a 'classic' NSS failure so I'd love some validation before swapping this.

 

[gsxr]

Surging throttle should NOT be related to the NSS in any way. You can swap it, but don't expect any change.

Top things that come to mind are either a vacuum leak (don't forget a leaking purge/MOT valve, btw) or an issue with the ETA.

 

[Yorkabenz77]

Surging throttle should NOT be related to the NSS in any way. You can swap it, but don't expect any change.

Top things that come to mind are either a vacuum leak (don't forget a leaking purge/MOT valve, btw) or an issue with the ETA.

I have an idle on my one 500 that sometimes doesn't bump.up.from 500rpm in park/neutral and do have a code for nss...
Other than that, it's fine. Would that be more of an adjustment issue?

 

[gsxr]

I have an idle on my one 500 that sometimes doesn't bump.up.from 500rpm in park/neutral and do have a code for nss...
Other than that, it's fine. Would that be more of an adjustment issue?

Try adjusting the NSS first, per FSM procedure. Next is viewing live data to see if the computer is registering each gearshift position correctly. If adjusted properly and still not showing the right gear, you'll get a fault code, and also could have 500rpm in P/N instead of 650rpm.