08-19-2008, 10:20 AM
Join Date: Jan 2008
Location: Ashburn, VA
Total Cats: 0
Emissions (1997) - OBDII failing...need help diagnosing
I've got a 1997 Miata, 138k miles. All stock except for the Racing Beat intake. I went to get my emissions test and failed. In Virginia, they do the OBDII scan. 3 monitors didn't pass (weren't ready). They are:
There are/were no hard codes, battery wasn't reset, no major work. The car runs fairly well. Relatively new spark plugs and wires (less than 10k). The car doesn't have the top end it used to...nor does it seem to accelerate nearly as quick as it did years ago.
I've run injector cleaners occasionally. It gets autocrossed frequently. Timing belt and other stuff done around 126k.
I've replaced the front O2 sensor recently. On my cheaper Acctron scan tool, it passed. However, when using a nicer Matco scan tool, it showed the 3 monitors "not ready."
The TPS (throttle position sensor) is only reading between 11% and 72.9% (doesn't show 100% full throttle, even though I have the gas pedal to the floor). My mechanic downloaded the specs from Mitchell onDemand and the voltage was within (right in the middle) of the accepted ranges.
Has anyone seen anything like this on the 1.8 Miatas? My mechanic didn't want to just start randomly replacing things (nor do I).
I appreciate any insight!