This mother berkleying NB1 Answer seems short on them...

Ok, so the stumble and die problem is back, again no codes for the longest time, and now it threw a P0123, tps.

Except that in pulling plugs and hoses to see what reaction I'd get, I pulled the tps, and it threw no codes when i did that. Shouldn't it have?

At one point I also got a high and wandering idle, which would've been consistent with the 1504 code I got two weeks ago, and from whence the car has been running flawlessly.

Until now.

I'd seen in Miata.net that occasionally an ecu goes bad - I did not consider that a reasonable possibility, but with funky running and no codes, should I?

This is maddening.

Ok, let me phrase the question this way:

What running problems have you had that threw no codes, and what was the fix?

ECUs very rarely go bad. Usually it takes a voltage spike or something. But a sketchy ground can cause all sorts of weird problems, especially with sensors.

Attempting to look up all the grounding points now, but, while it is certainly in the realm of possibility, how likely is it the car would run flawlessly for two weeks, and then up and die with essentially no codes?

Ground wires on top of TB are tight, all wiring looks/feels fine....

Pull the grounds and clean them throughly.

Just being tight won't solve the issue if there is corrosion that you can't see.

Also, wires can break or be broken and be hard to find the break if the insulation is thick or hard.

Start with the grounds, remove and clean them, verify connectivity at each end (wiggle the wire if possible) then reasssemble and protect them with Vaseline or a similar grease.

From there move to the data and power wires and repeat the process.

The ground under the brake booster is problematic, especially if the car's ever had a leak.

Ok, I've located three grounds in the engine bay, top of the throttle body, bottom front of the manifold, and the ground strap on the back driver's side of the engine bay.

First two look in pretty good shape, maybe a little bit of surface dirt, cleaned and shot with PB blaster (since it seems to break everything down...), and the ground strap at the back is fine.

If there are any more, let me know.

Cleaned the throttle body IACV/circuit, wasn't really much to clean, but I did it anyway.

Certainly open to other tips and tricks that others have used to solve a sudden death of the car with no codes.

I think the NB has the big multipoint ground under the brake master, no?

To properly clean a ground you need to disconnect it and bring both surfaces down to shiny metal.

Then, for good measure, coat the connection faces with dielectric grease..

Keith Tanner wrote: I think the NB has the big multipoint ground under the brake master, no? To properly clean a ground you need to disconnect it and bring both surfaces down to shiny metal.

The NB (well, my NB1 at least) has a big braided cable chassis-to-engine-block ground strap near the master cylinder. All of the electronics are grounded to the motor near the throttle body.

All surfaces are clean metal to metal, but they were pretty clean to start with. I did not use dielectric grease, but in SoAZ, there's not really much more than dust to get in to things.

And, per codrus, my NB1 grounds are c2e near MC; and throttle body. Replaced all the manifold vacuum lines, 4 in all, TB to mani, mani to a connector near the shock tower, mid-mani to connector on back side of shock tower, and a connector to connector line on the last connector.

Also took some MAF cleaner to the TB connectors, as well, see if that might get some dust/scale out of the way.

Let's see what transpires.

chase your vacuum lines and make sure none are leaking or unplugged, my focus suddenly wouldn't start, found that the brake booster vacuum line came off and it ran like a top after plugging it back in.

I've had random shutdowns on different cars sure to engine mounts and an intake tear..

I've never heard of it on a Miata, though, but it's easy to see how much engine movement and inspect the accordion for rips..

FYI, there's a big really important ground on the back part of the PPF. I don't know if it would cause sensor problems.

Could it be the crank position sensor? I just went through this with mine. Jack up the car take off the lower engine cover and clean the CPS. And make sure there isn't more than a credit card width between the sensor and the teeth on the pulley. If there is more than that I think it can be adjusted slightly. That cleared it up immediately for me.

I have tried to keep in mind Keith's wisdom as I go through the process here, and in another thread I had on this problem he mentioned that crank sensors rarely go bad (and the possible ecu problem I wondered about - on Miata.net I guess couple have lost ecu's - but if the man say "unusual" I usually cease that line of inquiry...).

But I shall check it none the less, what have I got to lose?

That said, with the latest go round, the car is again running better than it did before (not radically, but you can feel it), but the problem in question doesn't seem to care about that!

Cold, the car takes longer than it ever has to start, though, and it doesn't like to catch fire even then. It never had issues catching at cold start before.

And I'm trying to think, it may be that as temps warm up is when it happens, which is rather reminiscent of the cam position sensor problem except that it threw codes pretty consistently.

Who knows...

Unusual isn't the same as never We get a lot of guys who want to blame the ECU for everything because it's a mystery black box. It IS in the list of potential failures when you're running through the Mazda troubleshooting list, but it's always the last thing on the list.

Crank sensor air gap is definitely a potential problem, I think it's 0.040" or less. A loose bolt there could cause all sorts of entertaining symptoms.

Could be a good excuse for a mega squirt . Otherwise I have nothing useful to add

TurboFocus wrote: Could be a good excuse for a mega squirt . Otherwise I have nothing useful to add

Yeah, if it weren't for more or less "daily driver" status and a need to pass smog/OBDII connectivity, that & a set of cams would be on the way... why? Because spending big money to get little power is a hobby of mine...

Ok, more of the same E36 M3.

No codes. How many of you guys have issues with no codes?

With the fresh vacuum hoses, it still dies, but is "less intense".

I did get some wandering idle, so seems like the one code of the IACV i got two or three weeks ago, might be accurate?

Still need to check the crank sensor....

Ugh.

Anybody want a nice 2000 miata? Runs great!

Can you access to a real scan tool that can read the data stream and any freeze frame data? If not, it might be worth spending the money to buy one or to have someone look at it. I know we're all about DIY here but without access to the proper tools you're reduced to replacing every part the might possibly cause the rather generic symptoms that you have. So far that hasn't really worked very well although, I suppose it will eventually be successful.

Short story- weak fuel pump relay. I had a no codes problem in a 1995 volvo 850- all bosch stuff. It went on for months, low on power, suddenly stop running, stumblers, then run great. Even took it to a well regarded Indy to no avail. After many many new or junkyard parts (MAP, fuel pump, fuel filter, fuel regulator, junkyard ECU (That turned out to be an eyeopener but not the problem- the "tuned" ECU was stupid rich) grounds cleaned, yada yada yada) It was the bosch fuel pump relay. With a new one it went like a batoutahell. Weak relay for years apparently.. In reply to OldGray320i:

Yeah, someone ("professional") looking at it is next.

I've got a used IACV in at $20, some vaccuum tubing, and plugs/wires/coil pack (plugs and wires were due anyway...), so the 2 bones and change is more than I should've dropped in parts, but I really thought that was it.

Of course, it's also the reason I bought the blipshift shirt "Internet Certified - Master Auto Tech"...

OldGray320i wrote: Yeah, someone ("professional") looking at it is next. I've got a used IACV in at $20, some vaccuum tubing, and plugs/wires/coil pack (plugs and wires were due anyway...), so the 2 bones and change is more than I should've dropped in parts, but I really thought that was it. Of course, it's also the reason I bought the blipshift shirt "Internet Certified - Master Auto Tech"...

Hey, it was worth a shot to replace that stuff. I'm not criticizing your efforts so far. From my vantage point is looked like this was headed in a direction that was going to be needlessly expensive and still frustrating.

I love those shirts.

The mention of a relay somewhere is a possibility, so I'll check a schematic and see what ties to what; in theory, relays are cheap. I hate giving up, but/and, now we're back to the content of that t-shirt....