kalafre

1993 Taurus 3.0

Car went to what seemed like full throttle today. I find that when I disconnect the Mass Air Flow sensor, it will idle (roughly). Also, if I disconnect the hose from the throttle body, it will idle (roughly). This leads me to believe that the Mass Air Flow sensor is ...confused...
Does this seem like a safe assumption?

shorod

Yeah, after unplugging the MAF sensor and later removing the air inlet hose, the PCM was most definitely confused. It sounds like the MAF is doing what it's supposed to. When you unplugged it, the PCM no longer knew how much air was entering the throttle body, and when you removed the hose from the throttle body, unmetered air was entering the intake and really hosing up (no pun intended) the air/fuel ratio.

The throttle on your 1993 is mechanical, the only thing that could cause it to go full throttle will be mechanical in nature or the cruise control.

So can you describe the incident better? How long did it stay at what seemed like full throttle? Did it do this as you were accelerating aggressively? What did you need to do to get the engine to slow down?

-Rod

kalafre

I was trouble-shooting after the fact (this happened to my daughter).
Technically, it didn't go to fuel throttle, mechanically. Rather, it goes to high rpm's.
With the air intake hose (going from the air-filter to the throttle body) attached to the throttle body, the car was at super-high rpm's as soon as you started it. When the air intake hose was removed (allowing air directly in to the throttle body) it ran at normal rpm's, but rough. So I put the air intake hose back on and it ran at high rpm's again, so I disconnected the MAF sensor pigtail and it ran at normal rpm's.
So, MAF sensor connected, high rpm's...MAF sensor disconnected, normal rpm's.
My thinking is that the wire is not heating up properly, so the MAF sensor thinks a huge volume of air is flowing, so it tells the EFI to put more fuel in the system.

shorod

How high do the rpms go with the MAF and hose connected? Are we talking like 1500 rpms, or higher? You could also have a Idle Air Control motor that's stuck allowing too much air past the throttle plate. Or, you may have a carbon build up on the backside of the throttle plate that is preventing it from closing fully, but still allowing too much air to flow past it. When you disconnect the MAF, the roughness is making the engine run crappy enough to slow the engine speed. Most of the time a disconnected air intake hose would cause the engine to stall at idle. I think whatever is causing the fast idle is still there when you disconnect the MAF/hose.

-Rod

kalafre

It goes very fast - that is why I used the phrase "Full Throttle".
When the MAF is disconnected, it sounds like it's at about 400-500 RPM.

kalafre

I just wanted to follow up with the resolution to this.
Although the MAF seemed a possibility, it actually was something else.
Next to the throttle body runs a small conduit with two small vacuum lines. Somehow, this conduit worked its way to a point where it was binding with the throttle linkage, which prevented the throttle from closing fully.
1 zip-tie later and it's all fixed...

Thanks for the suggestions!