Air / Fuel Ratio going nuts. Car running fine... H


OK.. I just swapped a b18a1 into a 90 crx si.

My air/fuel guage is going NUTS! when I start the car, it runs rich untill it warms up. This should be normal. But once the car is warm, It dances from lean to rich to lean to rich, back and forth about once every second! The idle used to surge with it, but it seems that I have fixed the idle problems.

A list of stuff I've done:
Fresh new oil/filter
New Fuel Filter
Coolant air bleed out
Cleaned out EACV/IACV
Replaced FITV, opened it up and screwed the white screw in tight before I installed it.
New Oxygen sensor
Replaced all engine grounds with 6 gage. Added one. She's grounded now!
New Plugs, gapped properly
All new vacuum hoses
Vacuum is running at -22psi. Rock solid, no fluctuations.
Idle is 750, solid.
Set idle to factory specifications using the chilton procedure.
Timing is perfect, triple checked!
I put in my mugen chipped 90 CRX Si computer and it still had the same problem.
Engine idles great and seems to be running very strong.
No check engine lights

Things I haven't done that may pose a problem?!?:
Replaced the cap and rotor
Put fresh fuel in it. Fuel is around 8 mos old, I believe.. Trying to run it as low as possible before putting fresh fuel in.

The car was idling high (1000-1200) and surging back and forth at the same time as the air/fuel was surging.. But now after i've done all of that, the idle is rock solid at 750 RPM.

The fuel goes rich when I get on the throttle hard, and goes lean when I completely let off, which is correct. BUT, while cruising and idling the guage sweeps all over, and seems to sweep faster with engine speed.

Wow, that was a mouth full.. Any more ideas?


I'm just about that action Boss.
The A/f guage is only accurate if you have a wideband o2 sensor. I've delt with 4 of these guages, all autometer on four different swapped cars, and all of them did the same thing. It isn't a good monitor, but pretty much a cosmetic upgrade until you purchase a true wideband system.


Staff member
if its an autometer, that what it does.

it's why we call it "the laser light show"

get a wideband.


Whats bugging me is that its the same gauge that was already in the car before the swap. The o2 censor is the same part number. It worked fine before the swap. (running the si motor, the gauge was in there for a year) It would read stoic while cruising and idling. Of course it did fluctuate a little, but not like it is now. I'm still disturbed....

I'll figure it out. Thanks though.