Altitude Sensor Throwing Off Smog Results?

[91spiderNV]

Just bought the '88 Milano Verde from San Jose (sea level) to Reno, NV (5000 ft). Put on a new cat and muffler. The car failed smog badly.

Could the altitude sensor throw the car off this much? It still is running great, ignition timing seems good. Don't smell any gas, no smoke.

Car passed CA smog in July/07 easily.

Here are the numbers:

Here are the figures from 7/24, in San Jose:

15 MPH CO .4 HC 116
25 MPH CO .33 HC 90

Numbers in Reno 10/4 car was hot:

Idle (about 850rpm), HCppm was 618 limit is 220, CO% was 6.95 limit 1.20

2500rpm HCppm was 170 limit 220 (OK!), CO% was 1.97 limit 1.20

Air flow meter is clean, lamda sensors go bad? O2 sensor?

[slyalfa]

it might. I think you can check it with a DVM. but my guess is to retune it there anyways
download the shop docs.
if it was me I would look at the O² voltage(unplug big green wire) and ajust the pot on The AFM untill the voltage just start to swing back and forth. And then see where you are at.
you did change the oil 2 times and all the filters? use 20W50
read greg gordon L-jet tune up

[shoshone3]

Look for any and all vacuum leaks and exhaust leaks. Extra air to the O2 sensor will drive the mixture rich as the computer tries to compensate. Check all basics, clean oil, filters, grounds, and that engine is reaching operating temp. Bad temp sensor will keep engine in the rich "warm up" mode.
Do read Greg Gordon!

[Gubi]

Did you drive it for a while after installing the new cat? It supposedly takes 50-100 miles for the catalyst to reach full activity.

Other than that, yeah, go through Greg Gordon.