I have an '85 T/A, stock everything, pretty much original, even the injectors I swapped out, code F TPI. It isn't emissions exempt yet, so stock is good for now. The problem is, I can't get rid of a rough idle. I have an AutoXray, and according to the scan everything seems to be OK, except I do have a question about the MAF sensor readout. When it stalls at idle in drive, (really rough at times, but not until it sits a bit) the gr/sec drop like a stone like a countdown. However, when the motor is not running, ignition on, I get a reading of 8 or 9 gr/sec. Is this normal, or should I do a sensor and burn off relay? I have also heard of a computer problem related to the MAF "module". Could it be an IAC related problem? The scanner indicates a working condition, and it "steps" like it should, apparently, anyway. Any info would be greatly appreciated...

 

The problem is that you are reading scanner data, not the actual signal produced by the MAF sensor. The scanner will report only what the ECM is telling it, AFTER the ECM has performed the signal conditioning, scaling, etcetera. This is all great if everything is working correctly, but it ISN'T, is it? Too many techs were either asleep during that part of their training, or they got lazy and forgot exactly how the systems work.

Put the scanner back in its pretty case, and get out you DMM to perform some real diagnostics. Chances are that the meter will tell you exactly what is going on before the ECM, then you can use the scanner to determine if the ECM is FUBAR.

Remember that the ECM will assume a presumed flow value so that fuel can be administered during cranking, otherwise the engine will not start. That may be what your scanner is reporting, and you won't know until you test the MAF directly. This is the old design ECM after all.

Back to the root of the problem, have you performed a compression or cylinder leakage test? If the test(s) indicated proper mechanical condition, did you perform a power balance test of the ignition system? The injection system? One of those three should point you in the right direction.

 

Motor is tight, and I will perform the multimeter checks, and what are the specifics, if any, of common problems with the "old ECM"? And, hate to come up stupid (HA,HA), could you define a power balance test?