On a n/a what does this sensor contol besides secondary air....can it control idle??? The reason why I'm asking is when i tap on the sensor or wiggle the connector the idle speeds up and down is this supposed to happen??? I thought it only controlled the air pump system...??

 

Don't think of it so much as a boost pressure sensor but rather an intake pressure sensor. Under different loads and rpm's, your engine takes in different amounts of air. You could have 2 different times when you are at say 4000 rpm but depending on how much throttle you are giving it, it will have a different intake pressure, or more appropriately vacuum. Then ecu uses this information to help determine how much fuel to inject and how much timing to use based on rpm AND load. If you disconnect it, the ecu goes from thinking it has a good vacuum, to thinking it has near full throttle pressure since that is a lack of vacuum. This sensor still functions the same way on a turbo car too.

 

The boost/pressure sensor has NOTHING at all to do with the air control valve or the airpump. Absolutly nadda. We're talking about the boost/pressure sensor located near the right strut tower. One vacuum nipple on the bottom with one electrical plug and black and rectangular in shape. This is not in disagreement with the post above. Just want to make sure you know it has nothing to do with the acv or airpump.

 

so should this thing make the idle change if u tap on it???

 

so this sensor is kinda like a MAP sensor on most cars right??

 

Sounds like a poor electrical connection either in the plug or in the MAP sensor. If the ECU gets no reading from the MAP sensor it defaults to reading of ~4inHg vacuum, a bit less than what an NA sees at WOT. Once of the MAP sensor's tasks is ignition timing control, and since the timing settings at idle are quite different to those at WOT, the timing is probably changing each time the ECU loses and regains the correct signal, and this would definitely affect idle speed. That's my theory anyway.

 

hmm...ill try another one and see if it makes a difference...mines a 91n/a could i use one from an 89n/a???

 

You must use one from the same serise (4 or 5) and engine type (NA or Turbo), so yes.

 

I was just working on my engine in that area, and i accidentally nocked off the hose to the pressure sensor. It looks like it was glued on or something by the previous owner. Is it bad to drive with the hose disconnected? Anybody know where i can buy a replacement hose connection?

 

To the original poster- might want to do a search- we discussed this little bugger in detail a couple of months back. Even went so far as to disassemble one to interpret the guts, lol...Basically, a small pressure-sensitive microchip inside of an enclosed cylinder is the "pick-up" medium for our intake pressures (or vac, if you will), this signal is very small, and must be amplified prior to output to the ECU. Hence, any slight bumping may very well skew the output signal.

Like NZ said, it could very well be a dirty/loose electrical connection also...

Now, to the last guy- a broken pneumatic input won't disable the signal output, but the ECU will think your manifold pressures are at atmospheric all the time (akin to WOT), and will adjust fuel scheduling accordingly. In other words, she won't run like she's supposed to. And, if you happen to have error code LEDs installed (S4), or the S5's check engine light, it should be continually telling you that something is wrong...

 

is there anyway to check the pressure sensor with a multimeter?? or osope??

 

Yes, read the FSM.

 

The output of the pressure/boost sensor is found at pin 2B at the ECU. It's a brown/red wire and should read approx 2.3 to 2.7vdc if the car is a turbo and 3.5 to 4.0 vdc if a non non turbo..... at IDLE and fully warmed up. Idle being approx 750 rpm.

Or, if you don't want to access the ECU, then unbolt the pressure/boost sensor and backprobe the brown/red wire at the sensors connector with it connected up and the car idling.