Have any of you ever taken a car in for the tailpipe sniff test, only to have the engine start running badly when they put the probe in the tailpipe, and smooth back out when they remove it?
The first time it happened, I thought it must be my imagination. And the car wasn't running well anyhow, so I wasn't surprised it flunked.
The second time it was running smoothly. The moment the probe went in, it started getting rough. But it was when he pulled it out and the engine immediately smoothed out that I was sure this really did happen.
I've never heard of this, don't see how it could happen. It was a long probe, I think he did shove it all the way up into the muffler (god knows why). I can't duplicate the results so far.
Yes, this is the Miata with the weird low rpm roughness that goes away at 2000 rpm. That's doing better at the moment. Not perfect, but much better.
Do you know if the sniffer pulls a vacuum to get a reading?
not that it should matter....
Have you tried to partially block the exhaust? (gloved hand, of course... 
)
Wonder if your car is super sensitive to something.
The only thought I had was that the sniffer touches or clips onto the exhaust somehow completing or shorting a circuit.
There's nothing wrong with your car, I don't like probes up my tailpipe either!
Ok, now for the serious post:
I was thinking you could try to replicate the problem with a broom stick?
If the problem arises with the stick then you would know its a "plugged exhaust" issue, if the problem doesn't duplicate itself then you could suspect "electrical circuit" issue... either way, that's kind of odd.
Spent some quality time with the car last night. I just can't replicate it, and really can't see how it's possible anyway.
The car's been keeping me occupied with various things past month or so. Payback for years of rock solid reliability I guess.
Temperature sensor for the ECU is cheap, I'm going to replace it. I've been finding several sensors that are borderline, and I think this one is as well. I really suspect it isn't ranging as far as it should, causing the ECU to never know engine is actually fully warm.
