I missed your earlier discussions; I'm assuming you're putting an '89 engine into an '89 car, and you kept the same ECU and fuel injection system.

Fault in fuel injectors. I would test it. The four injectors are wired in parallel, connected to a single output at the ECU. Pull the plug off each injector and measure resistance. Each should be about 16 ohms. Plug them all back in and measure at the ECU terminals. You should see about 4 ohms. The ECU will only "see" the injectors electronically, so it's registering an unusual current situation.

Fuel system compensating for rich or lean mixture at cruise. If one of the injectors was partially blocked, you might get a misfire on that cylinder, which would be seen by the oxygen sensor as over-rich, and it would lean out the whole system, causing the rest of the cylinders to run lean.

Vehicle speed sensor missing: There is supposed to be a wire from the speedometer in the dashboard to the ECU. It's a blue/black wire that goes from pin 34 at the ECU to a 12 pin connector on the instrument cluster. (If you have an older car that you put a newer engine into, the older cars have a mechanical drive for the speedometer, while the newer cars have an electronic sensor in the differential that drives the speedometer.)

If you haven't already done it, you might want to check and set the base idle speed and the base mixture setting. If you can't get the base mixture setting to come in line, it's usually indicative of something else not working somewhere. Once you get it all working properly, you can set the base mixture, and it should run happily from there.

With the codes you're seeing, I definately suspect the fuel injectors. If you have injectors from your old engine (assuming the same year swap) you might try swapping the injectors and see how it does. One other thing - if your fuel pressure regulator was sticking, that may cause similar fuel system "weirdness".

Good luck!

Roger

It seems to me that your engine is running lean. Normally, the mixture is controlled by the ECU so that mixture is almost normal (lambda = 1).

If the mixture is lean, and the O2 sensor still works, you can measure the voltage of the O2 sensor (connector is on the firewall, right side, green wire). Connect a digital voltmeter this connector (+ terminal), the - terminal to ground. When the mixture is lean, the voltage is below 500 mV (0 to 250 mV). When its high (600 - 800mV), the mixture is rich. With a normal working engine, the signal is travelling between lean and rich, with a cycle time from about 0.5 to 1 sekond.

If your mixture is lean, the reason can be : fuel injectors, pressure regulator, AMM. Most suspicious to me is the AMM (had the same problem years ago).

You can fool the AMM, so that the mixture will be richer :

Take it out the car, take away the inlet screen, inside you see a little tube with the hot wire in it. Don't touch it !. Make an obstruction between the innertube and the outer (some foam will work). Mount it again.

Now, the engine will run richer, because the AMM thinks there is going more air through it (only the inner tube is measuring !).

It worked fine for me (now for 4 years).

Good luck.