First, not said, but let's assume there are no codes. If you've got
codes, stop reading now.
You've got the right idea. Don't start, "throwing parts at it." Could
be something as simple as an emissions cannister purge valve or fuel
tank vent valve being screwed up. On an '89, check to make sure the
tachometer is reading correctly. If it's reading high, the engine will
run rich--common cause is stray signals getting into the ECM due to a
busted ground wire on the distributor shielding.
Generally, the MAF signal comes into play during changes in airflow, not
during steady state operation. If the throttle is closed the MAF isn't
in the picture. Think of the MAF and the Throttle Position Sensor as
doing what an accelerator pump and dashpot accomplish on a carburetted
engine. Steady-state running is more dependent on the O2 sensor and
computed Block Learn. If the MAF circuitry is not throwing a Code 33 or
34 there are better places to start looking.
Get Section 6E (Drivability) of the maintenance manual. Run a scan.
Follow the troubleshooting diagrams--avoid jumping to conclusions.
Guessing and prayer won't help. (Praying for increased patience is OK).
The results of the scan may pinpoint the issue. At the worst, the scan
will rule out a lot of stuff that's difficult to reach (like the EGR
valve on an L98) or difficult to electrically test. If you can't
borrow, build or rent a scanner, paying a couple of hundred bucks to
have someone else diagnose the problem is money well spent.
Get a fuel pressure gage--good for checking on fuel pressure & exhaust
back pressure. Also enables a simple injector balance test. (Cheaper
than paying someone to flow-check injectors.) Again, replace the bad
part, don't throw 8 injectors at a balance problem. Pick a gage that
will measure 0-60 psig and let you read a 1 psig (or 5kPa) increment.
'89 auto coupe, '02 e-blu coupe
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