Hello... I'm working on my brother's 1984 240 wagon, B23F, with LH 2.0 injection, US spec. The car is running EXTREMELY rich. It idles poorly, misses horribly at higher RPMs and spits/barfs out huge black clouds of unburned fuel from the exhaust. I pulled the spark plugs and saw that they were saturated with raw fuel.

I got my blue Bentley Volvo 240 manual out and dug in.

Upon examination, I found that the air mass meter (AMM) was bad, it had a broken filament and the idle mixture potentiometer couldn't be adjusted.

I pulled the connector off of the AMM (ignition off, of course) to put the car in limp-home mode. It runs much, much better in all RPM ranges this way, but stalls a lot while driving. Obviously, I can't leave it that way.

I installed a rebuilt AMM, but the problem persisted with virtually no change.

I tried various mixture settings, with no changes or improvement noted. I did a full test of the rebuilt AMM according to the Bentley manual, everything checks out to spec, including the mixture potentiometer (both at the AMM and at the ECU connector) and the power supply and ground at the AMM connector.

I replaced the oxygen sensor. Voltage at the connector reads at 1.0 volt and drops slightly when coming down to idle from 2000 RPM, then goes back up to 1.0 volt almost immediately; there is a simultaneous drop in idle when this happens. I am not getting the fluctuating voltage that the Bentley manual says I should get at idle.

I connected a noid light to each fuel injector connector. Each flashes like it should when I crank the motor.

I've removed and thoroughly cleaned the throttle body and reinstalled it with a new gasket. No improvement. One item of note here is that I can't seem to get the idle down to spec, even with the adjustment screw turned almost all of the way down.

I checked for throttle switch function and continuity, both off of the manifold and at the ECU connector. It is working perfectly and set correctly, both for idle and wide open throttle.

I've checked for vacuum leaks as best I can. Nothing found so far, but I suppose that it's not out of the question, although a leak would seem unlikely to cause the system to run so rich... would I be wrong to assume that? I examined the entire intake system from the air cleaner to the throttle body, there are no leaks or other problems that I could find. The air filter is clean, the preheated air system isn't a problem, either.

I've checked the idle air control valve, both at the ECU terminals and using the idle test connector. It appears to be functioning normally, I get the expected 200 RPM drop with the test connector grounded.

The coolant temp sensor read about 1,500 ohms at 75 degrees F, which seems about right according to the Bentley chart.

There is no cold start injector on LH 2.0 systems, so that rules that out.

I've done a complete LH System Electrical Test according to Bentley, page 241-12. The only item that was out of spec was the AC microswitch; there was continuity no matter where the AC switch was set, I got a reading of about 5 ohms on my meter.

I have had several electrical connections go bad on this car and my '82 due to corrosion (fuel pump and ignition systems were affected), and am suspicious that a wiring issue might be the problem, but the ECU test (mentioned above) didn't show such issues... anywhere else I should look? I should mention that I rebuilt the ubiquitous disintegrated wiring harness by the firewall last year... I will check it all again for good measure.

If I'm not mistaken, the ECU gets its RPM signal directly from the coil, and I haven't checked that circuit yet... could that cause my problem? The car wouldn't run without it, correct?

I have not checked the fuel line pressure regulator, but if it was the culprit, wouldn't it cause problems whether or not the AMM is connected, since it is independent?

I am now considering that the ECU might be bad, but I don't want to throw $$$ at replacing it until I've exhausted all other possibilities. ANY hints or info appreciated.

Thanks for reading this far... I'll check back regularly to see what the collective has to say!

Victor
Portland, OR