Gas w/ethanol causing drivability and C.E.L. problems?

Hello, does anyone know if gas containing ethanol causes the check engine light to lite?
My C.E.L. lites at idle and then goes out when I speed up.
I get a "rich fuel exhaust" trouble code #45 for my '87 Olds Cierra.

I've replaced:

O2 sensor.
MAP sensorAnd checked EGR valve to make sure it moves freely, port is not clogged, vacuum lines to it are good.
There's no change.
The car runs fine and has a good idle.
I've checked the plugs and wires.
Any ideas?
Note:
I posted this question here in this section because, if the gas is the problem, it applies to a wide range of cars.
Thanks.

If it only happens at idle, try cleaning the idle air control valve. What engine in in your car?

2.5L.
I thought about the I.A.C., but it seems to control the idle ok, and I don't get any trouble coses from it. It couldn't hurt to clean it though.

Engine misfire, dirty injectors, high fuel pressure, fuel contaminated oil all can cause this code, ethanol at 10% is not the issue, are you trying to use 85% ethanol?

I use whatever the local gas stations are selling.:confused:
It has a T.B.I. The only way the fuel pressure can be higher than what the pump can produce would be a clogged return line from the T.B.
I doubt that could happen, although stranger things have happened.

Wrong, how about the pressure regulator in the TB having a torn diaphragm. No way to know without checking the pressure, normal diagnostics for a rich condition.

to answer the first question, 10% ethanol would definitely NOT cause any code.

If you used a much higher percentage of ethanol, such as E85, it very well might set a lean code, but not a rich code

As for figuring out your problem, you replaced the two items I would have suggested off the cuff. If you haven't done it already, I would definitely be checking fuel pressure.

Misfires cause lean codes btw. It definitely won't be an ignition problem, EGR problem, vacuum leak, etc. Very few things cause rich codes

Wrong, how about the pressure regulator in the TB having a torn diaphragm.
I appreciate all the replies.

Man, good point maxwedge.
You're right. If the diaphragm is leaking, the pressure will not be able to open the return port for the gas to return to the gas tank. I'll have to look into this.

Or it could be the injector itself... did you run some fuel injector cleaner through the sytem? There could be deposits inside the injector that allows it to sitck open and not allow the proper cone shaped spray into the throat... either that the whole injector could be damaged.

I've been dealing with the problem over the winter, but I have to go thru emissions now. I'm getting desperate. I have to go thru emissions or the registration will be suspended.
The throttle body injector doesn't leak when it's not running, but perhaps it could be bad.
I've checked the fuel pressure which seems to be correct. It's steady at 12 psi, and then increases to 20 psi with the return line pinched closed.
I'd rather fix it myself than pay a shop hundreds of dollars.

Does any one have any more suggestions?
I've cleaned a couple of the grounds for the wiring harness and cleaned the main connector for the harness.
Thanks a lot.

Anybody?