Recently, I've worked on three cars with Mass Air Flow sensor problems. None of them triggered an engine code

General process:
* Ensure harness attaches tightly to the MAF. Ensure the pins of the connector are good
* Inspect MAF sensor for cleanliness
* Inspect engine for airflow leak (vacuum leaks)
* Don't replace the MAF unless damage can be verified
* When all else fail, check Fuel Pump PSI (not usually a problem at idle, more likely to be a problem under high load/high RPM)


1. Nissan B15 1.8 would idle fine, as soon as you touched the throttle it would die. Cause: dirty sensor, didn't look shiny. Fix: $7 can of electrical contact cleaner, spray the sensor several times until shiny silver appears. Let dry 5 minutes. Been running great for six months

2. Nissan B15 SE-R 2.5 (QR25DE) would idle fine and rev OK in neutral. Shake when put in gear. As you tried to move the car the engine would shake badly until it revved up a bit, then it smoothed out and had plenty of power. Cause: Air leak on downstream side of air duct (flexible ducting was cracked in two places) -- as the engine moved, it opened up the cracks. Solution: Replace air duct

3. Mazda 3.0 would idle OK, but shake when put in gear. Ran fine at higher RPMS. After a couple months it started misfiring at higher RPMS too. Cause: 1) air leak 2) MAF dirty. Solution: Clean MAF helped a bit, but still run slightly rough at higher RPMS. On inspection, MAF appeared to have rust on the sensor. Remanufactured sensor for $80 fixed the high RPM problems. Then I heard hissing from the engine at idle, so I removed the plastic engine cover and using a tube to my ear, narrowed down the location of the hissing. There was a large vacuum hose broke off. Put it back on and the engine quieted down, idled about 300 rpm lower, and stopped missing when put in gear. Like a new car!


* The Nissan B15s (2000-2003) won't run if the MAF is unplugged, apparently these ECUs require MAF to operate

* The 2003 Mazda 6 ran great with MAF unplugged, poorly with MAF connected (with the MAF unplugged the ECU estimates airflow via lookup tables, instead of sensing the airflow). This indicates an air sensing issue, though not necessarily an MAF sensor issue. For example, a good MAF will report less airflow than actual if extra air is entering downstream of the sensor. Downsides of running with MAF unplugged: engine codes triggered, and no modulation to the gearbox -- every shift banged hard. But a good diagnostic to confirm it's an air flow issue (in this case it was an air leak at manifold hose). This is the North America Mazda 6 with Duratec 3.0 V6 (Mondeo engine type). Dunno if it uses a Mazda ECU or a Ford-type ECU

Handy info , $700 later my exa turbo is still back firing and jolting after 3000 rpm. 2 mechanics and 1 auto elec couldn't find problem.