Gio

Harrumble! :clap: :happybday:

Other have suggested that - but I haven't got round to it yet because it's been fine on those plugs since 2014. And I don't understand why that would cause the over-lean and high IACV. Got a set on order now, in any case :)

Spent hours on this yesterday with Simon. Short version, TPS set to 0.48v (any lower and it won’t idle). Hard idle switch checked. This is the only actual change that’s been done – before it was at 0.54v. Now it occasionally stalls at low revs e.g. during parking. So if anything, this adjust has made it a tad worse. Fuel filter OK. Fuel pressure OK. Plugs look OK, lean, beige. They’re Bosch FR7KPP33U Smoke test OK. IACV operates 0%-20%-80% when tested. O2 sensors both operate – one is lazy and switches 1 sec (the blue one – LH bank, bank 2), the RH/red switches every 2s. Manual says more than 5 times in 10s so both within spec. Unplugged the O2 sensors in turn – no change. At idle, unplugged the MAF, it stalled. Going from idle to WOT, MAF peaks around 3.4V (green), blue is LH O2, red is RH O2 compression test OK scoped all injectors – all the same This vid shows the IACV valve reacting to the stumble and getting the revs back. Then it goes down again until the next stumble. [video=youtube_share;AM-qSguKPto] This vid shows more IACV top right, revs top left. Simon pointed out the timing (on the right 6 down) isn’t as stable as he’d expect, nor is the CAS reference (middle, bottom). [video=youtube_share;uEATuevD-6I] There are more vids on this . The only change was adjusting the TPS from 0.54V to 0.48V and that’s made it a tad worse! We’re stumped. Have we missed something obvious? If not, next steps could be to change out the O2 sensors, put some NGK PFR6B-11 in. If that doesn’t work, pull the injectors and take a look – even though they scope OK, they could be dirty, not spraying correctly. I’m going to run some injector cleaner on the grounds it can’t hurt. All words of wisdom gratefully received especially if you’ve had this “15 sec stumble at idle” and cured it. Cheers!

Looked at the O2 sensors yesterday and they are the earlier type. Don't know why they are fitted to S6 but there you go. I emailed ConceptZ and, as helpful as ever, Nick said: Cheers.

Thanks. Going to try that today. And the MAF (also suggested by Jimmer). PS do you know if the earlier O2 sensors (Bosch 13091) will work with a late car / ECU? https://www.300zx.co.uk/forums/showthread.php?187997-Replacement-O2-Sensors&p=1959352&viewfull=1#post1959352

Thanks. I'd prefer the Bosch but the 13091 is the earlier type - the first one in Jeff's post. The later ones have a different part number and are the 2nd ones in Jeff's post. Has anyone used the early type with the later 16 bit ECU / late car and do they work or do I need the later type. Jimmer says he's got a pair of the earlier in stock. Cheers.

Found this while looking for info on O2 Sensors as I might need some new ones (see here). From Amayama I think the part numbers for what JeffTT says are the early 8 bit ones are: 22690-30P00 (RH 89-87) 22690-40P10 (LH 89-97) but take JeffTT's warning on dates and for the later cars (the lower picture) 22690-46P00 (RH 98 on) 22690-46P10 (LH 98 on) The Nissan prices seem to be £hundreds so I followed that ebay link, did a bit of searching and came up with that our usual sources have the earlier type but the only place I can find the later type looks like a US aftermarket: https://www.ebay.co.uk/itm/New-Oxygen-O2-Sensor-for-1986-2001-Infiniti-J30-Q45-Nissan-200SX-300ZX/173761332026?hash=item2874fb833a:g:kLoAAOSw6EpcS3ZI This says they're the same as 1986-2001 Infiniti J30 Q45 Nissan 200SX. They are "inexpensive" - has anyone used these? Cheers, Mike

Thanks nickz32, will pass that on.

update 5: at idle, lambda is 1.4 (v lean) and fuel pressure 35psi. Then, as nickz32 mentions, took the hose off and it went to about 43. Then used a pump to add a bit of overpressure and got it to 45psi with a lambda of 1.089. Fuel filter changed May 18. No vac leaks that he can see / hear. Voltage not yet checked. The diagnostic thing is a Launch X431. This has tested the IACV valve through 0% - 20% - 80% and then back to 0%. Coolant temp 89C MAF voltage at 1,900 1.4V, at wide open 3.5V When the revs stumble at idle, lambda goes high (lean), O2 sensors react, ECU widens injector pulse from 2.5ms to 3ms, revs recover, after a few secs goes lean and stumbles and round we go. One of the tests says Bank 1 is lean, another says LH bank has better emissions (i.e. better mixture) than RH bank. Is Bank 1 the RH bank? I'm told the usual thing it that Bank 1 is the one with cylinder 1 which, since Cyl 1 is on the RH (facing forward) would mean Bank 1 is RH bank. One of the O2 sensors switches at half the rate of the other. I've asked which is which and at what speed. Simon is going to go through all the data he's found over the past few days and I'll post the key points later. I'll go up there at the weekend and see if I can get my ConZult working and compare notes. So any pointers as to specific tests or readings or thing to look for will be gratefully received. I'll try to take some vids as well. Thanks for your help, guys - being on an island, it's not easy to drop by one of "our" known specialists so all this is very helpful. Ta :thumbup:

Thanks nickz32 - he said he did it with his kit but I'll ask the q when we speak later and I pass on your tips. There was a leak on the fuel damper > balance pipe tube but fixed that. @ Joely P thanks, will try to do that when I go up there.

update 4: The "stumble every 20s" happens higher up the rev range as well not just at idle, noticed this when warming up for tests. TPS / hard switch set and checked. MAF reads up to 3.5 at rpm. IACV valve operates OK when checked directly. O2 sensors switch rich/lean about every 3s (believe it should be every 2?). The only thing that seems to cure is when he sets higher fuel pressure with his scan tool. He's going to stick the scope directly on various things and also measure voltages directly - MAF, O2, injectors. Any suggestions? He thinks - as JeffTT does, it's ECU compensating for something, the revs recover, then the ECU returns to base and the problem recurs. Then round we go again.. Thanks.

update 3: what's this unknown tube? Looking around for damaged vacuum hose, Simon found this tube under the RH inlet manifold which exits at rear of manifold. Appears to be redundant. Is it? PS thanks nickz32, will pass that on and ask.

update 2. Further digging around shows: there's no EGR control valve there's no AIV control valve solenoid the TPS seems to be good the IACV/AAC is at 56% so that's too high. Simon reckons this is trying to compensate for a vacuum leak somewhere and wants to take the manifold off to inspect and test the IACV/AAC to see it can operate through full range. Before that will check / clean throttle bodies. Any other pointers? BTW I noticed in the 1996 manual (US market) that doesn't show AIV solenoid but does show the EGR. Does anyone know if the 99 NA should / shouldn't have these? Thanks

Update. Tech bloke says his diagnostic thing doesn't show any issues higher up the rev range so, as mentioned here, IACV is next on the list to check. I've asked him to recheck TPS/hard idle as well. What he saw on Sat is that, at idle, the mixture goes lean (more on bank 1), the revs drop, the ECU increases pulse width to compensate, the O2 sensors see the mixture going richer, revs rise back to 750 or so, idles smoothly then mixture goes off again and round it goes again. More tests later today. Cheers.

Happy Birthday, old bean. :rockon:

Thanks nickz32 - Consult first said that IACV-AAV was at 0%, then some time later, OBD Scantech said (pics earlier in thread) Idle Air Valve 59%. Is that the valve you mean?

Hi Daz, not specifically just yet. The TPS (without any foot-on-pedal) is currently reading 0.52 / 0.54 v which is not too far from the 0.46v mentioned by JeffTT and the 0.4 - 0.5v range I've seen elsewhere. Would this reading cause the intermittent stumble? This is not "rough idle all the time" but "idle is stable for 20s, then something happens, it skips a couple of beats, then something happens and it goes stable again until the next 20s skip". So I think JeffTT's comment " the ecu is trying stabilise things." is on the money. The engine diagnostic bloke who is looking at it had a similar comment. There hasn't been any work on the engine that might have triggered this. I'm guessing that if it was an injector or other generic issue, it would idle rough all the time. As it is, seems like something the ECU can adjust for a bit, then it goes hiccup.

When warmed up, she idles smoothly for about 20s, then skips a couple of beats, the ECU catches it and runs smoothly again for about 20s, then skips, and so on. This is without throttle. Once throttle is open, runs smoothly. So it's not rough all the time. When driving its fine, except when no throttle. One suggestion is something to due with fuel pressure but don't have the detail until tomorrow. Any bright ideas? Ta, Mike

Hi Richard, no problem - the thread nearly got into double figures before hurtling off into the middle distance which is about standard for here :) . Should never have used the S-word! We're fine thanks, hope you and yours also :flowers:

Throwing a few things from the parts bins at an end-of-life production to wring the last few sales out of it is one thing. But there were some very costly changes to create the S6 at a time when they knew they were selling less than 800 a year of what was a 10 year old car. A new mould for the bumper and new tooling for "thicker structural members" are far from trivial. I discount the window switches as I know they really are just a raid on the parts bin :) It was not a sensible financial investment. Maybe Joely P's idea to bridge the gap was part of it. I suspect the new front bumper was a reaction to the new-at-the-time Supra but haven't checked the dates.

Thanks. I'll be very interested to see that when it's done. Is there a timescale / anything that we can do to help? If you look at the changes they made to Series 6 (e.g. "thicker structural members", "increasing the size of the brake master cylinder and changing the booster characteristics", front bumper, window switches, new glass - those are common to all models - plus so many options: xenon headlights, leather, spoilers, TT, VR and VS and more) why did they bother for less than 1,000 cars?

A couple of questions prompted by a couple of AndrewG's posts https://www.300zx.co.uk/forums/showthread.php?190273-A-great-way-to-spend-a-Sunday-morning&p=1988126&viewfull=1#post1988126 and his link to http://gtr-registry.com/en-nissan-300zx-z32.php 1. FAST gives the production date of my Z as 9904. Is there a way to get it even more precise - to week or day? It seems it's got a birthday coming up so want to give it the card at the right time :D 2. It's a shame the GTR Registry link doesn't cover JDM production. Is there any reference to when Series 6 production started (and how many were made, when)? I guess I could manually step back through VINs but that would be a tad tiresome. The factory announcement was made 7 Oct 1998 but refers to "release" so I don't know if that means they'd already made some or were starting to make them. https://newsroom.nissan-global.com/releases/release-622e2183c9ca29da3ef1a7b00701c437-fairlady-z-undergoes-minor-model-change?query=300zx Assuming the Oct 98 date is production start and production was even throughout the year, that means they made a grand total of 828 Series 6.

Spotted one vacuum leak so better check the rest. Also found several threads eg https://www.300zx.co.uk/forums/showthread.php?151629-Hoses-needed-for-300zx which says I need 4mm and 6mm - but that is for turbo. Found the manual lists 14 bits of vacuum hose but doesn't give the size. Does an NA need both 4mm and 6mm? Thanks.

Thanks Jeff, hope all's well with you guys out there. The OBD bar display was grabbed first and 154 F is about 68 C then after a few minutes, I got ConZult working and temp was up to 81 C so that seems about right. The video was taken after a 5 mile drive and about another 10 mins at idle but I didn't check the displayed temp (will do next time). What would you say was fully warmed up? There's no boost issue (NA). I'll check the plug type / records tomorrow. If anyone can advise the vacuum tube dia, that would help save me a trip across the island. Cheers, Mike

Hallo. A few days ago, my S6 '99 NA Auto started to idle roughly / misfire at idle. It's OK while driving but when off throttle (junctions, stopped etc) it idles roughly and feels like it's only the ECU keeping it going. If left to idle when parked, it runs smooth then about every 20-30 secs or so, it misses a few beats then runs smooth again. That happens about 10s into the below video. I managed to get ConZult and OBD ScanTech running but not sure what to look for (listen, I can help you build a new fibre network but as for my Z, I lift the bonnet, go "hmm- hmmm" and reach for an expert - which is you lot :) ). I've looked through a number of the rough idle threads here and have noted to check: good connections on each coil pack, plug, injector, vacuum leaks, AAIV connectors, O2 sensors, MAF. It's all completely stock. Plugs last changed Mar 15 only done 32,000m since. No error codes. In case I need to replace any vacuum tubes, what dia are they and will any type do? Here's the pic of the auto balance check: And here's the bar display from OBD Scantech: And here's the vid - hiccup about 10s in: [video=youtube_share;ul9EhNqiJsQ] Any suggestions for further tests gratefully received. Thanks.