Hey guys,

I've been battling the Q's idling problems. I had a bad coil which was throwing a code and I replaced that with a hitachi coil which seemed to have fixed everything. However recently, my rpms have been periodically dropping and sometimes coming back up and sometimes stalling the car. Theres no codes other than a knock sensor but Ive been told that it isnt a big deal and that because theres multiple sensors its unnecessary to get it replaced. Its only stalling when I come to a stop and car is preforming normally under other conditions/when driving. Only stalls in drive and reverse. I've seen a couple of threads talk about the MAF but since it doesn't affect driving at higher speeds I didn't think it would be that. I've also seen spark plugs and coils but I'm not getting any codes and the spark plugs and coil are OEM (or equivalent like Hitachi) and are in pretty good shape. Please help!

logmanQ45 wrote: ↑

Thu Sep 30, 2021 2:39 pm

I've seen a couple of threads talk about the MAF but since it doesn't affect driving at higher speeds I didn't think it would be that

The MAF does affect engine performance at all speeds, especially on engines with no MAP sensor (which is most naturally-aspirated Nissans and Infinitis). Without a MAP, N/I ECM's must simply trust the MAF because they have no means to cross-check it. Thus, bad things happen when a MAF lies. Moreover, when you perform an Idle Air Volume Learn (IAVL), the ECM is not only learning the "baseline" reading, but also the slope. That's why the idle fluctuates slightly during IAVL, because the ECM is measuring delta and calculating a correction scalar that will apply across the RPM range. It doesn't take a butterfly wing to cause problems, either. I've seen MAF's that were off up to 30% just from "component drift" with old age and never being IAVL'd. So in any stalling situation with no codes present, the very first action you should take is cleaning the MAF(s) and performing an IAVL. If that doesn't fix it, then go on to the next thing.

Alright I'll try that and get back to you

Problem that I'm running into right now is either taking it to a shop that has a 2 way scanner to do the test (or dealer who quoted me 179) or being able to rent a scanner or even buy one. Does anyone have any recommendation on something that would be able to do the IAVL?

You don't need elaborate equipment to clean the MAF. Search old threads, there should be some how-to ideas.
Just don't actually touch the element, and don't bugger up the harness connector (although the later ones were much more robust than on the early Q's.
As for the IAVL, I've been out of the FGY33 game for a while, but I actually don't recall that there was this capability on the VH41.
I absolutely agree that the IACV (the control valve) can also get gummed up with age, and in my estimation will be the #1 cause of a 'hunting' idle on a VH41.
Does your '99 have the 14-pin gray connector on a drop out tab, right under the steering column underdash?
If not, then you'll need an OBD-ii nissan specific scanner (that does not mean you MUST go to nissan for the scan) to read the duty cycle on the IACV.
the duty should be 10-15% at warm idle in park, AC off.

logmanQ45 wrote: ↑

Fri Oct 01, 2021 12:34 pm

Problem that I'm running into right now is either taking it to a shop that has a 2 way scanner to do the test (or dealer who quoted me 179) or being able to rent a scanner or even buy one. Does anyone have any recommendation on something that would be able to do the IAVL?

3Q Jay wrote: ↑

Sat Oct 09, 2021 10:36 am

As for the IAVL, I've been out of the FGY33 game for a while, but I actually don't recall that there was this capability on the VH41.
I absolutely agree that the IACV (the control valve) can also get gummed up with age, and in my estimation will be the #1 cause of a 'hunting' idle on a VH41.
Does your '99 have the 14-pin gray connector on a drop out tab, right under the steering column underdash?
If not, then you'll need an OBD-ii nissan specific scanner (that does not mean you MUST go to nissan for the scan) to read the duty cycle on the IACV.
the duty should be 10-15% at warm idle in park, AC off.

Jay will know a lot more than me about the specifics of your "oldie", so I'll defer. Thanks, Jay.

VStar, your knowledge waaaay impresses me. I just know a few things specific to these old cruisers.

3Q Jay wrote: ↑

Sun Oct 10, 2021 8:43 am

VStar, your knowledge waaaay impresses me. I just know a few things specific to these old cruisers.

I was in a different end of the business doing engineering for 25 years, so a lot of "details" about stuff between 1987 and 2012 are vacancies in my knowledge base. When it comes to those, I'm happy to defer to guys like you and Mdmellot who have owned the subject vehicles and have a wealth of "hard knocks" knowledge about them. The forum is lucky to have you, and so many folks like you.