1990 244DL

I was getting a check engine light with the codes 232 and occasionally 113. I would disconnect the battery to reset the computer and after about 125 to 150 miles the light would come back. So I bought a meter to test whether I was running lean or rich at idle. Here's what I get.

The car starts up fine. Initially after startup, the meter would read stoich - i.e. fine. Then within ten seconds the readout would drop slowly into the lean range and then off the scale. Results appear to be verified with a mutimeter. I checked for air leaks and can't detect any. I changed the exhaust including o2 sensor, FPR, cleaned trottle body, changed main pump, upgraded the 561 ecu to a 951, did a complete tuneup, etc. I'm just stumped as to what would cause the guage to register off the scale. I mean, a small air leak should make it run lean, but this gauge just eventually drops right off. If I shut the car off and wait a few seconds then turn the key to the II (two) position without firing up the car, the meter slowly returns to stoich. With the multimeter I verify that I am getting.5 volts before startup. The car seems to be running ok, at shakes a bit at idle and once the light comes on it really starts shaking a bit. What could be causing me to run so much in the lean range? Thank you.

My first thought was also the accordian air intake hose, my second thought was the intake manifold gasket which were already mentioned. Both are quite easy to replace and not too expensive either.

Bean
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'80 242GT 93k, '94 945T 143k, '89 765T 68k (new '94 B230FT)

The 84 DL had this problem along time, until I pulled the intake manifold and replaced the gasket. Problem solved.
It' sjust about impossible to detect, and the job is not too hard. You just have to pull the manifold off the studs, and make sure you get all the old one off.
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745 & 744 16valves w/ 4+OD, 245 SE w/auto, 242 Ti w/4+OD, 245DL parts car

Pull off the 'accordion' plastic intake tube between the AMM and the throttle body. Stretch it to make sure there are no cracks in it. They may not be visible unless you look at the tube carefully and flex it around. Could create a huge unmetered air leak.
Did you check all air connection around the idle control motor? Is the idle motor functioning properly?

vytas

The usual culprit is a vacuum leak; air that gets to the motor without traversing the AMM. Also, exhaust leaks and inoperative or clogged injectors, but you say you replaced the exhaust.

The "stoich" reading you see is only while the o2 sensor is cold and not generating any response to the motor. If you disconnect the sensor from the ECU, leaving the A/F meter connected to the ECU, you'll see "stoich" all the time.
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Art Benstein near Baltimore