Well, I've got it. On the '98 SSEI."SYSTEM TOO LEAN - BANK 1" Looks like it could be a long day tomorrow No other codes.

History...
-A week or so ago, i gutted the air box. The boost gauge changed and indicated what is often a vacuum leak. Couldn't find it. (Boost gauge running -9 instead of -10 when stopped at a light.

-Replaced O2 Sensor

-Two days ago, I cleaned and replaced the TB.

-yesterday got gas and added the Chevron fuel system cleaner.

- Today engine light comes on, on the way home. Boost gauge gets heavy, -10 at stop light. O2 sensor is reading positive values, instead of + and -.

So here'* the top of the hit list, from what i have read from you guys...

1) Check routing of plug wires, make sure everything is away from O2 sensor.
2) battery cables checked and cleaned. And battery.
3) Check the fuel pressure next, because it'* quick.
4) Start soup to nuts with the carb cleaner again, to check for a vacuum leak. Add in around TB.

Any suggestions and possibilities would be appreciated. Speculations and questions on highest probability welcomed. If it'* the fuel pump, I'm going to be even more pi$$ed than I am right now. The car has been running great since I have been reclaiming performance with the BC best practices work.

O2 sensor and battery stuff OK.

Tell me about the IAC. There is a vacuum leak either at the IAC or on the TB, near the same spot. My bet is the IAC because there is no bolt head on one side of it. There'* bolt inside the tap, but no head. Must have weakened it when I reattached it. I'm going to have to retap it or reverse the bolt out.

Could a draft on the IAC caused all of this? It'* a mechanical valve, controled by the PCM. the freeze frame indicated it was at almost idle speed when it threw the code.

Even if it isn't the problem, I'm going to have to straighten it out before i continue.

First of all, please post the Techinfo description when you post a code number, so we don't have to go look it up. This is a courtesy to those you want replies from.

Any and all vacuum leaks need to be proven and repaired before going further. Spray carb cleaner at each location while the car idles. If the pitch or tone of the idle changes, there'* a leak. Your IAC has an o-ring. It probably isn't leaking with only one screw holding it in.

How old is the O2? What brand is it? What'* your alternator output at idle? Battery voltage at idle?

Yeah, I guess giving the description would be considerate. I put it up top "System too lean - Bank 1." I used the carb cleaner to check all around the TB and right where the IAC connects, the engine stumbled. So I straightened out the bolt problem, put the IAC back in, and checked it with carb cleaner and it held.

I had a no-name O2 sensor in the car, pulled it a week ago, and replaced it with the AC-Delco per BC tune-up standards, along with Beldens, NGK55s. I swapped back in the no-name O2 sensor to see if the Delco had failed. I got the same slow readings I had with the original. So the Delco appears to be OK, it'* just quicker. (BTW, the week old Delco had more carbon than I expected)

In my searches, BillBoost had problems with this code. And he'* a strong proponent of checking the battery cables. I checked them all (not look, took 'em apart). They looked good at both ends, ground etc, but I sprayed them and reattached everything.

I need a decent fuel pressure gauge, so I'm going to pick up one now. I'll confirm the readings on the battery and alternator while I am there. We'll see what comes of those and the fuel.

I cleared the code and it stayed off for an hour on the road, but I think it takes a few cycles to pick up this code. Meanwhile the car seems to have lost it'* "jump". I need a lot more thottle to get the boost gauge to push into the "+" side.

when you checked the fuel pressure did you pull the vacum hose off the FPR?

I just got the fuel gauge. Nice little unit, an Actron. Supposedly, you can check the pressure at the rail outlet, the FPR, clogged line, and the pump itself. I'm out of time to fuss with it today. first thing tomorrow. I'll keep in mind your thought about the FPR.

Alternator 14.5
Battery 13.2 , (amps read within normal range, too)

When you check it again you should see an increase in FP when you remove the vacume line. If you dont see an increase your pump is probably not able to provide enough flow under a boost situation. Possibly due to a clogged filter or a weakening pump.