So, my understanding is that OBDII and the related check engine light is more for emissions problems than anything else.
Manufacturers may have developed proprietary diagnostics as well but that would be stuff that standard obdII readers cannot really get to.
Intermittent problems are THE WORST.
Remember that vacuum leaks can come from more than just hoses. Gaskets, fittings, anything past the MAF really.
Robbie wrote: So, my understanding is that OBDII and the related check engine light is more for *emissions* problems than anything else. Manufacturers may have developed proprietary diagnostics as well but that would be stuff that standard obdII readers cannot really get to. Intermittent problems are THE WORST. Remember that vacuum leaks can come from more than just hoses. Gaskets, fittings, anything past the MAF really.
That's sort of true. The OBDII standard defines codes and data that all vehicles need to provide and the individual manufacturers can add to that. A code reader will just, as the name implies, read codes. A scan tool will read some data stream(s) and maybe stored freeze frame information while a good scan tool with manufacturer specific functions can access much more data as well as perform some special diagnostic routines.
I have no idea what the options are for a scan tool for the Miata in question but if I owned one and wanted to do my own diagnostic work I'd investigate that.
Even with all of the tools in the world intermittent issues are the worst.
I enjoy driving this car.
But Imaburnthismotherberkleying car to the ground....
Runs great, like really great, for a good while now, but after auto-x today, same e36 m3 as before.
Down to the shop it'll go, but gahdammittohell, this is maddening....
So in looking at the codes you've received combined with the symptoms, it really sounds as if the issue is related to either the wiring for the throttle body (think about it, the TPS and the IAC both acting up at different times?) Or perhaps somewhere along the path those wires take back to their termination points.
Think about it: The IAC keeps the engine at idle, especially after coming to a stop. The ECU reads the throttle position off the TPS and knows when the engine should be idling. If either or both are not working properly, then you can have a stumble and hard to start situation. Also keep in mind, the ECU is watching for sensors outside of their range, if the TPS or IAC are within their ranges, but not in the correct positions then no codes may be set.
You could try pulling the throttle body and cleaning it thoroughly. Remove the IAC and the TPS, carefully break them down, then clean and lubricate them thoroughly. Then run through the TPS and IAC adjustment procedures. Connect the TPS to the car, but leave it off the TB, turn the key to on and turn the TPS with a screwdriver with a volt meter connected to two leads. Measure the TPS range with a Volt meter to ensure it smoothly provides 0-5V from idle to WOT, any jumps or huge swings and you'll know they'll have failed. At their heart, they are simple rheostats and they wear and fail overtime.
In reply to Stefan:
It seems to occur with heat, and with every touch this touch that gets a little better. Correct me where I'm wrong ( I know this in advance! ), but TPS, if not working, ECU would just tell it to "run rich" yes?
IACV I got was used, but in all my readings on Miata.net, that's not something that pops up as a failure point. But, pull the little vacuum hose from the bottom of that circuit, it'll kill the car, so problems with that unit would seem to be a definite possibility. I'll have to find a way to test that, or it's associated wiring (and I did look the circuit up on that in the "find the loose ground" phase, don't remember what it ties off too...).
Yesterday afternoon, after it cooled a little, I got it off the side of the road in to a parking lot (where it stumbled and died...), and it threw the 1504 (no other identifier, prior it listed IACV) and 0170, I think (lean bank 1).
That said, let the car cool for a couple hours, fired right up, drove perfect.
Could it be the connector on the cam sensor? Apparently a known problem Spec Miata fix
P0170: Bank 1 - Fuel Trim Malfunction
Detection Condition:
Fuel injection closed loop correction and learning correction are above the specified value because of system malfunction.
Possible Cause:
Fuel injector malfunction
Fuel pump malfunction
Fuel filter clogged
Fuel delivery hose clogged or leakage
Fuel return hose clogged
Pressure regulator malfunction
Pressure regulator control solenoid valve malfunction
Purge solenoid malfunction
PCV valve malfunction
Ignition coil malfunction
Distributor malfunction
High-tension lead malfunction
Spark plug malfunction
Leakage in intake-air system
Insufficient compression
Leakage exhaust system
MAF sensor malfunction
Engine coolant temperature sensor malfunction
TPS malfunction
Front O2 sensor malfunction
Vehicle speed sensor malfunction
Open or short circuit in wiring harness
Poor connection of connector
Vacuum hoses damaged or loose
In reply to cmcgregor:
That's interesting. I'll give it a whirl when it happens again...
In reply to Stefan:
I'd wonder about some of those, but the car runs flawless and strong in between, and while any of those could kill the car, most seem more akin to poor running condition that outright "death" (and resurrection after cool down...).
I'm looking at the list and I see MAF, TPS and IAC on there and it would fit with your other described issues.
Certainly if the connectors are questionable, especially when heat is applied, you could see a cascading series of issues.
Any chance you could buy or borrow a spare ECU? I'm just wondering if you might have a bad solder joint or intermittent connection at the ECU. I realize that ECU failures are rare, but its not exactly unknown either.
If I do anything before I take it to a shop, it'll probably be to find an IAC off a known running car; it's the only code that's been thrown more than once, no other codes referenced have - and if the unit I replaced is the reason that car wound up "salvaged", well ironic (though unlikely to me such would be the case... does not seem a common failure part; that said, neither are ECUs, but there were several miata.net posts with running issues like mine where it turned out to be the case).
That leaves other issues, but which would seemingly cause a more consistent problem (i.e. not running flawlessly, in between), wiring, of which I can find no breaks or bad grounds (and why cmcgregor's note is intriguing), or an ECU. From memory, IAC wires straight to ECU, it's not dependent on other circuits, but I'd have to look again. ECU was one of the culprits I initially thought was a possibility, but I suck at diagnostics, so I'm trying to chase "easy" stuff first.
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