Car passed everything (easily) except low speed (15mph) hydrocarbon emissions. The value measured was way high and the tech said it is just running wayyyy rich at low speed. During high speed test the hydrocarbons were well within tolerance (almost nil).

WTF???

I am about done putting money in this car, it is time for someone else to work on it.

 

HC alone doesn't indicate rich or lean, too lean or too rich & the HC goes high.
along with some other things, a misfire will also cause high HC.
if you can, scan the failure sheet or post the numbers, HC, CO, CO2, O2 & NOx.
if you scan the sheet, fold it so your VIN & tag numbers don't show.

 

OK,

 

he is right, it was rich on the low speed test, 4.14 on the CO shows it.
i doubt there is anything wrong with the cat.

a few things that can cause that,
possible but unlikely, it wasn't fully warmed up.
possible problems,
fuel pressure regulator intermittently sticking causing high fuel pressure or injector problems.
most likely problems,
the O2 sensor could be weak, a problem with the air temp or coolant temp sensors. a MAP sensor problem, TPS problem.

check to see if it has any codes, if it does, post them up.
if it doesn't have any codes, you'll probably need to get a data log to see what going on.

 

The only code that ever comes up is the EGR code (32). It does sound like it misses some once warmed up. All ignition components are new.

I can't get my laptops serial port to work, so I have never been able to collect data.

 

not being able to get data will be a problem.
which programs have you tired to scan with?
if it misses on the side of the motor the O2 sensor is on, it could fool the ECM into thinking its running lean. normally for it to boost CO that high, you would know its missing

something else i just thought of that i left out, problems with the AIR injection system.
i have seen a few diverter valves stick & put fresh air into the exhaust manifolds, it causes the O2 to show lean & the ECM thinks its lean & adds fuel.

 

I thought it was pretty much determined the AIR system only helped the cat light up and then it was done its job as far as emissions go...

 

the AIR system does help to get the cat warmed up when the motor is cold by injecting fresh air into the exhaust manifolds, it does this by helping the burn process to continue in the manifolds which lowers emissions during engine warm up. after the motor is warm, it injects fresh air into the cat to help it do its job.
if the diverter valve sticks, it can cause fresh air to be injected into the manifolds after the motor has warmed up. it takes very little fresh air to cause the O2 sensor to send a signal to the ECM that the motor is running lean, even an exhaust leak that is so small you can't hear it near the O2 is enough to cause problems.

 

My understanding was the complete opposite, that is, air into cat during warm up and then "sporadically" into the manifolds during normal running.
I'm really confused now...:-(

 

See my recent post: https://www.thirdgen.org/forums/tpi/...ml#post3441187

I can say with certainty that that an improperly functioning EGR valve will cause a rich condition.