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Ok so background. I started experiencing this a month or 2 ago. Basically after driving for a while and then finding myself in stop and go traffic I noticed that when I have the clutch engaged with no throttle the idle would start to pulse. So today I set out to reproduce this issue.

Car details:
Lotus 7 powered by 1.6 miata
M45 Supercharger
MSPNP2
Wilwood Pedals - Clutch switch has been bypassed via attaching the 2 wires together.
All the idle warm-up parts have been removed from throttle body and intake manifold.

Other notes not shown in video below - On occasion when doing this it seems a cylinder will stop firing. Not sure if this is related or not. But this is even harder to reproduce, and will start working again as soon as I give it some gas.

So here are the details of the test:
I started the car, with just the key no clutch. Then let is warm up till the fan kicked in. Then I hopped in the car and pressed the clutch, this sent the idle pulsing. Released clutch and it stopped. Pressed Clutch it pulsed. ETC. Finally I blipped the throttle and it went away. See video here: http://youtu.be/5_VESPXs-wc

So anyone have any ideas? Best guess right now is the neutral switch, but don't have an understanding on how that could be causing this issue and why the clutch would play into it, when they is no signal being sent for it.

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Dave, the fact that your air bypass equipment has been bypassed or removed means that you cannot use closed loop idle, As a result, as you load the engine you will see a decrease in RPM. Fan on, lights on, both add load as do the brake lights. Pressing on the clutch pedal also adds load, possibly changing the Ve target cell to a different load row and RPM column. It seems to me that you may be hitting a lean cell just around that 1330 RPM idle point and maybe just below that 1330 RPM. I don't know what your Ve table looks like. I'd try adding one or two or three points to the cells above and to the left of your 1330 Idle cell and to see what happens. All the other times, when it doesn't hunt, the idle speed is around 1050-1150 RPM, probably working on a different VE cell. Don't know what is with the different idle speeds. Could the throttle cable be binding up somewhere?

Other notes, Idle speed is pretty high for a warmed engine, but that shouldn't matter for this issue. And your fan hysteresis could use a few more degrees, probably start with adding a few degrees to the switch-on temp.

_________________
Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

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pilot bearing in the end of the crank

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So I also posted this on the Atlanta Miata forum, and heard from one of the guys from DIYAutotune who makes the ECU. They think it might be the overrun fuel cutoff being bumped on. In the past when it happens, its happening in the lower rpm range of 1050-1150 so I don't think its specific to 1330rpm in the fuel table. So I have turned that off and will run another test tomorrow. Not a huge deal either way, just a funny bug, actually hoping its the overrun as I really liked the sounds it made prior to the tuner enabling it. But I'm not blowing your idea off either, as this started after the last tuning when I had them attempt to tune it for emissions. It's possible its hitting one of the leaner section of the fuel map.

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Doubt it, pilot bearing is brand new, and this only occurs at idle. Would think that would be across the board.

_________________
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Hi. Might be a idea to check the end play in the crankshaft, worn out bearings can cause lots of extra
friction.

My guess (based on some, but very little experience) would be the over run fuel cut. I started experiencing weird idle events when I turned on the fuel cut. Mine needs some tweeking.

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Larry in Seattle

Hi. If it was the overrun fuel cut, it would show up as a big change fuel mixture, save a file when it happens, open it in megalogviewer, should show what's happening.

Agreed rad. Dave's display has AFR (Lambda I believe) displayed. I'm not sure what the two other readings are. When it is susceptible to the RPM hunting, Lambda is running in the 0.8's. When it is stable, it is around 1.0 But watching what is happening on a log or even live in Tuner studio tells so much more than the dash display. I don't think it is fuel cut but it might be. Might also be decal enrichment setup poorly. Not enough info right now to tell. I have seen poor setups where fuel cut can be entered under 1200 RPM. Not good IMO but who am I to say what works on Dave's car. Tomorrow will tell......

_________________
Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766

Ok so I'm not exactly sure how to explain this other that tell the story.

So after Saturday I went about trying to test this issue further, only to find that I may or may not have a copy of the map on the ecu. Usually it prompts me when there is a difference between the ecu and the map on my laptop. But it didn't prompt me, and it probably should have since I don't believe I had plugged in my laptop since it was last at the tuners. Anyways, I switched off overrun and it seemed to be a bit better, as in I could not reproduce it via the method I used on saturday. But thats not saying much since its tricky to reproduce anyhow. However I stumbled upon something interesting. When I started the car on sunday it didn't fire right up. Then when I was done I shut it off and tried to fire it back up, but the battery was dead. This isn't terribly shocking since it has a small braille battery and that thing doesnt have a huge capacity. So I put the charger on it and got it fired back up, then put a volt meter on the battery and noticed that when running I was still only pulling 12v. Which led me down the path of a bad alternator. I pulled the alternator and took it to the autoparts store. They tested it and it failed one of the tests, so I got a new one. Installed it fired it up and still only 12v. So I check fuses, all are fine. Then I start watching youtube videos and stumble upon 1 talking about a miata whose dash and alternator has stopped working at the same time due to a blown meter fuse. I double check the meter fuse and its fine, so I pull up the wiring diagram and start tracing the alternator wire in question and realize that it runs directly into the dash cluster through a bulb and into the meter fuse. The problem being that I don't use the original dash cluster and since the info I followed for trimming the harness was made by a guy reusing the cluster I never actually connected the 2.

So with all that said, for the last 10 months or so it appears that I have driven nearly 1300 miles without a functioning alternator. I 'm not sure how this is even possible, other than that I plugged the trickle charger in after long trips and that there are minimal electrical systems running on the car. Which leads me to wonder if this was the problem that I have been having. Long drives, that leads to sitting in traffic with fan running and then the voltage gets a bit to low, then funny things starts happening.

How is it even possible that I have been driving this long without the alternator producing juice.

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Hi. As they say low voltage and computers don't mix well, lots of mystery stuff happens.
An alternator needs power from the battery warning light to it to start charging. Sometimes with higher rpm an alternator will start charging on its own.
A cheap tablet an shadow dash will keep you informed.
May be your tuner didn't make any changes, or does he use your computer.

So got a copy of the map from the tuner today. He upped the rpm on the cutoff and made some other tweaks based on the video. But with that said I think it was the alternator at the root of it. I ran the test today after resting the car for a few days and could not reproduce it, nor does it hunt for idle any more. Car fired cold at 850rpm and warmed up to 1150rpm with a steady 14.8 volts.

So moral of the story is, check that wiring diagram. I probably would have missed it anyhow, and if that is the worst wiring issue I have with the wiring, I'll take it. Thankfully I had the decency to leave the gauge plug with the remaining wires I couldn't or didn't feel like tracing accessible, so it was just a matter of crimping in a extension wire and splicing into the wire on the fuse box.

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Up to date build information can be found here:
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Whatever the root cause, it sounds like you have it licked. Congrats!

_________________
Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766