Another CEL code question...
 

Well, wouldn't you know...

Top down ride home from work, 65 degrees and clear blue sky, and I look down and see the CEL on! Got home and pulled a P1128 code, which is an enrichment limit code for cylinders 1 - 3. Like the sig says, 2000 S, no mods, stock air filter, 52k miles.

So here's my thinking... no 1130 code, so it's just one side right now, so it's probably not something that both sides have in common. There's no smoke at startup, so AOS is likely ruled out. MAF, fuel delivery, or vacuum leak problems should kick both sides, so they are out. Pretty much leaves O2 sensors. Or course, I guess that given a few more drives 1130 could pop and then this is all out the window.

Other possibilities or opinions? Anything is welcome, Thanks!

Jack,
Your reasoning is pretty sound. Clear the code, check your gas cap and drive to see if it returns. If 1128 does come back I suspect it's little buddy 1130 will follow shortly.

There are two types of P1128/30 codes. Above Limit and Below Limit.

Above Limit means that the A/F is running so lean - at idle, that the DME cannot richen it sufficiently with the maps it contains. Below Limit is the opposite, meaning that the A/f is so rich - at idle, that the DME cannot properly lean it out.

Here's what the DME 7.2 diagnostic manual says about P1128 (and 1130):

Above Limit:

P1128/P1130 - Fuel/air mixture so lean that sensing has reached its rich threshold.

Possible causes:

– Incorrect signal from MAF sensor
– Intake air system leaking
– Fuel pressure too low
– Volume supply of fuel pump too low
– Fuel injectors fouled
– Exhaust system leaking

Below Limit:

P1128/P1130 Fuel/air mixture is so rich that sensing is up to its lean threshold.

Possible causes:

– Incorrect signal from MAF sensor
– Fuel pressure too high
– Fuel injector leaking
– EVAP canister purge valve open

Note:

If DTC P0445 (EVAP canister purge valve – short to ground) is stored in the memory, correct this fault first. An open EVAP canister purge valve can lead to the lean threshold being reached. Contrary adaptation values in connection with misfiring point to adjusted control times - check control times and adjust if necessary. If the fuel tank reserve light is switched on, no fault is entered.

There are values for tests of the various components mentioned. If you want these, PM me with an email and I can get them to you.

Damn
 

Maaaaaaaaaaan, I was gonna come into this thread and try to sound smart, but I can't top Lil' Bastard (love the screen name, huge James Dean fan). However, I would almost say that with no mods, your luck is that it is probably the O2 sensor(s).