Background: My car has been running on a Brain built ms2 for maybe 5 months now, no big problems. I recently changed my clutch/flywheel, but the car has been fine and I don't see how that would effect anything. My car is still N/A, and I'm using the LC-1.

Anyway, I start the car this afternoon to go to work, and it won't hold a steady idle. Doesn't die, just surges between 400-700 constantly. It is very hot here, mid 90's, but the car normally idles fine regardless, and has been running great all week.

This behavior continues all the way to work. As soon as I get on the gas, the car behaves almost normally, but is reading very rich. Under cruise/normal load I read 10.5-11.5, and when engine braking it still stays around 12, doesnt lean out as it normally would. The last oddity is when I go under heavier load, the AFR goes to about where it should, around 13. Idle is also reading 10-11 when normally it is 14-14.5

I don't know much, but my first actions were going to be recalibrate lc-1, and clean the iacv.

Please help a noob here that's trying hard to find a solution before I have to drive home! Thanks in advance! I will datalog the ride home.

 

What are your current sensor readings? All normal?

 

Sounds like something is wrong with your TPS. Either it needs recalibrating, or something went boo-boo with the wiring or the sensor itself.

Dimitris

 

Which sensors? Coolant ok, oil pressure good, afr explained, there's a million sensors


Recalibrate in MS? I'll try that, want to explain how it causes these symptoms? Not doubting, I just want to understand



Thanks guys keep em coming! Sorry I can't give much feedback since I'm at work

 

Fluctuating idle = MS not entering closed loop idle -> possible cause = TPS, MAP too high

Overrun fuel cut not activating -> possible cause = TPS, MAP on overrun too high

Closed loop not working when crusing (indicated by being overly rich): possible cause = TPS reading too high, MAP reading too high, RPM too high

We can eliminate MAP being too high because your AFR on WOT is ok. The common possible cause for all of these symptoms is the TPS.

Dimitris

 

nice, the Athenians still got it

but it didnt help

 

tps was not the problem. Behaves just like before.

help
here's a log after startup.

 

bump for help? Maybe this should be in the general section? I'm thinking it may not be a MS problem

 

The only sensors I was curios about are the ones that dictate fueling. AIT, CLT, MAP and RPM. I could care less about oil pressure and the other 999,995. I was trying to establish the state of the ms because I can't see it from 650 miles away.

If you say they're good than they're good. I was wondering why your PWM IAC duty cycle trace is flat at 37.9, though. If your controlling the IAC valve it should be anything but steady, shouldn't it?

Bad IAC valve? Corrupted tune? Just throwing them out there in case you haven't already thought of them.

Vacuum leak would cause similar symptoms as well.

 

I had an IAC fail and stick open. Basically, the rpm would jump between 900 and 2500. But it would also impact while on steady cruise....

You should check the IAC....

Dave,

 

The log shows your MAP hovering around 63-65 kPa. On a normally running Miata it should be around 30 or less at idle. That suggests vac leak, or maybe an IACV problem, or something related to your MAP sensor or the vac line to it.

 

well, i checked my vac lines before posting anything here so i didnt think that was it. So I cleaned the IAC, helped a bit, recalibrated o2, didnt do anything, reset tps, didnt help, changed plugs and checked vac lines again. It must have been a vac leak because now it's running well. I never found the leak but that's what it seems to have been. Sorry guys that's what I checked first but I guess I just missed it the first time.

Thanks for all the tips though, I've learned a little bit more through this, thanks again everyone for always helping me out with my stupid problems