Smog nazis and HC

[FTA1995]

Nice, glad you passed.
now the million dollar question, dirty MAF or Dirty Filter?
Probably a combination.

I'm guessing the idle cleaned up then as well?

[Craig 94 TA GT]

The O2 in the air combines with the C in the gasoline. If there isn't much O2 available (rich mixture), the combustion is not complete, and the C + O = CO (carbon monoxide). If there is an excess of O2 (lean mixture), the combustion is complete, and the equation is C + 2O = CO2 (carbon dioxide). The more O2 that is present, the lower the CO and the higher the CO2.

The other part of the combustion equation is the "H" portion of the hydrocarbons (fuel). 2H + O = H2O.

At low combustion temperatures, the "N2" is just along for the ride.... it does not take part in the combustion process. But as combustion temperatures increase, and with a surplus of O2, the N + O starts to combine and form various oxides of nitrogen (refered to as NOx for convenience).

That makes sense, thanks for the explanation, Fred.

Nice, glad you passed.
now the million dollar question, dirty MAF or Dirty Filter?
Probably a combination.

I'm guessing the idle cleaned up then as well?

Thanks, I'm glad I passed too - I did not want to go the "illegit" route. The idle still has major issues right after resetting the PCM. When I loaded the new fan settings, I also reset the PCM. When starting right after, the idle was horrible again. It surged between 400-1200 RPM and died once. After driving for 5-10 minutes, it was fine again. I think it's time for a new IAC and adjustment of the stop screw. Idle shows IAC counts around 60-90. Generally it's around mid 60s to low 70s, but sometimes it seems to "stick" around 90 and go down slowly, right after coming to a stop. That's why I'm thinking it's sticking.

[Injuneer]

The IAC "counts" you are reading with the scanner is the position the PCM is telling the IAC motor to set. There is no feedback to tell the PCM what the actual IAC position is. If the counts stay at 90, its because that's where the PCM is telling it to stay, not an indication that the motor is "stuck".

If the idle is rough, the PCM is going to have to open the valve up more to keep the RPM up and keep it from stalling. I'd say its not an IAC problem, its a poor idle quality. When you reset the PCM you are losing the long term fuel corrections (BLM's) and resetting them to 128 (0% correction). That would indicate the long terms have a significant deviation from 128 after they are fully "learned". You have to check the BLM's and if they are making significant fuel corrections, figure out what is causing them to do that.

[FTA1995]

how much spark correction + or - you get on average at idle?

[Craig 94 TA GT]

Thanks guys - I always overlook the real causes as you pointed out it could be BLM correction. And with 160 idle BLMs, you are probably right. I am seeing 27-31* of advance. I attached my advance vs stock. The RPM range os 0-4000. I think I need a retune really soon.

[FTA1995]

Check the Idle spark timing and take the average of what you see for 15 seconds, should be off by many degrees at all, one or two maybe that should be it. I can't really tell you that from your main spark table. If theres a big pull in idle timing, the IAC could be jammed open. We need to see gm/s idle, a few seconds of timing readout, they should be synced at least close to time, JUST in the idle, lets see what we can see.

If your timing is still the same as the MAIN you sent m e before, The IAC maybe be stuck closed or might just need to be relearned.

[Craig 94 TA GT]

Check the Idle spark timing and take the average of what you see for 15 seconds, should be off by many degrees at all, one or two maybe that should be it. I can't really tell you that from your main spark table. If theres a big pull in idle timing, the IAC could be jammed open. We need to see gm/s idle, a few seconds of timing readout, they should be synced at least close to time, JUST in the idle, lets see what we can see.

If your timing is still the same as the MAIN you sent m e before, The IAC maybe be stuck closed or might just need to be relearned.

Ok, I'll scan and check it out soon.

I still think I have a weird issue with the IAC. In the cold weather, I start the car to move it 1 spot in the driveway, shut it off. I start it again within 20 minutes, and it won't start unless I hit the throttle. It's fine then after that. I don't know if hitting the throttle helps because I'm giving it some revs/gas, or if it's simply because I'm opening the throttle blades. I'll try to find out soon.