Hi I have been having a problem with my 4runner not wanting to rev past 2000rpm after it gets warm, and I have another post all about it if you'd like to read it. Basically it will act as if it has a rev limiter at 2000rpm .I thought I had fixed the problem after cleaning a ground terminal for the ECM, but today the problem persists. I figured that I should rule out the Volume Air Flow Meter (Mass air flow). So while it was giving me the problem I pulled over on the side and unplugged the VAFM and the 4runner died after like 10 seconds, and I heard that its supposed to be able to run with it unplugged. So my questions are:

Why did it die?
Could I have a faulty VAFM?
Could my problems be related?


PLEASE HELP I NEED HELP THIS IS DRIVING ME CRAZZZZY, ALOHA!

 

Where did you hear that? What do you think the VAFM does?

First, the VAFM measures the air flowing into the engine, so the ECU knows how much fuel to add. Without the VAF, all you did was blind the ECU.

Second (and probably more importantly), the VAF has a switch that detects when "some" air is flowing. If you get into a crash that breaks a fuel line, you want your fuel pump to stop ASAP! That switch (through the COR) stops the fuel pump when the engine stops sucking air. Unplug the connector, the COR opens, the pump stops, the engine stops.

Your VAF is probably fine, but you read the manual to get the diagnostics.

 

I read that if you unplug your mass air flow sensor your car will still run. I guess the VAFM and MAF is not the same thing like I thought it was. Thanks for the information, I am glad its supposed to die.!!

 

#nailed it

Could try jumping off the diagnostic for fuel pump. But don't see why would just run in open loop.

 

You might want to tell us just what year and engine your working on??

Could be throttle cable adjustments or something broken.

 

Check your:

TPS...
Vacuum lines...
Throttle body...

 

They are different technologies (the VAF measures volume, a MAF actually measures mass), but they serve the same purpose. Meaning: if you disconnect a MAF you've still blinded the ECU. Because the fuel injected depends on the air flow, it isn't like the ECU could use a single "default" reading to replace the missing MAF.

While I could think of a way that I could design an ECU to "limp home" with a disconnected MAF, I've never heard of any manufacturer trying it. I would be careful of what you read (yes, especially here).

 

VAFM has a switch to the fuel pump. So when you unplug it there is no fuel supply to the engine. The VAFM must be open a little to close the switch so the pump runs, its a safety feature to cut off fuel to a dead engine and prevent a really bad fire.

 

Vehicles using a MAF typically are programmed to calculate air mass based on throttle opening and RPM in the absence of a MAF signal.

 

The actual problem sounds like fuel delivery. It may have enough to get the truck fired but not enough to increase the speed the motor turns. I would look at fuel pressure regulator then the fuel pump itself.

 

You are probably thinking about the tps that people unplug and the truck still runs. And with what your truck is doing,I would lean towards it being a tps related issue,my friend just had the same problem. We found a wire that was barely holding at the tps plug,and when we took the cheap aftermarket tps off (that we just put on a year ago) the insides fell out.