MAP sensor? Anyone?

[JWC]

Hi,
Every now and then I drive around and the ECP and Check Engine come on. After a restart the ECP goes out and then after 4 more, the Check engine light goes out. Other than that, car runs ok. Sometimes a soft missfire in second after ragging in 1st.

I plugged in my VAG-COM and it will have one fault code (only when the check engine light is still on.)

MAP Sensor Implausible Signal. -Intermittent.

Now, I've checked the harness to the sender and its ok, and I have looked at the output. It reads about 1000mBar when the engine is static, and about 300 when its idle, and climbs to about 800 ish with Wide open throttle. This looks about right to me. It does say intermittant, so perhaps there is a problem. But I have ruled out everything except...

1) The sensor is faulty, but pretends to work when you watch it (a bit like me when I was at school).

2) There is a vaccum leak somewhere.

3) The K&N filter is affecting the manifold pressure, and this is causing it.

Anyone had to have the MAP changed. As soon as I mentioned MAP sensor to someone he said 'is it a VW?' Which lead me to belive that MAP sensors for VW's might be less than perfect.

Anyone know how much for one? And it is the sensor on the end of the inlet manifold, if I wanted to measure the pressure that is where I would do it.

[Josh_PoloGTi]

I took the sensor out and gave it a clean in isopropyl alcohol... That sorted mine.

[JWC]

I took the sensor out and gave it a clean in isopropyl alcohol... That sorted mine.

What problem did you have? I've read that the MAP can produce glitches if it gets a problem. Mine seems ok then goes a bit bonkers. Just had all the bist off the engine, checking for obvious vacuum hose leaks, but seems ok, and an idle reading of 300mBar sounds plausable. So perhaps it needs replacing. Did yours have carbon on it? Why would IPA fix it? The diaphram can be attacked by IPA?


Hmm IPA - reminds me, went to beer festival yesterday, mmmmmm beer.

[Josh_PoloGTi]

Huh? What diaphram?

Mine had thick gunge all over it...

The car was running a bit lumpy and I was trying everything to get it sorted.

[PhilGTi]

Josh i have the same problem, which sensor did you clean and where is it located in the engine?

[giannispolo]

Guys the MAP sensor what does it do and where is it located in the lump?

[JWC]

The MAP sensor (Manifold Absolute Pressure) is located very close to the dipstick on the inlet manifold. Its job is to tell the ECU what the pressure in the inlet manifold is, so it can work out how much air volume there is going into the engine. It knows how much goes in, because it knows the capacity of the engine, and if it knows the pressure, it can work out how much fuel it needs to get 14:1. Its about 1" by 0.5" with one screw at either end.

It is basically a pressure sender and gets the pressure by comparing it the force on one side of a diaphram with that on a calibrated side. The bigger the difference, the more the silicon bends. But it can give a scratch output. Basically, as I understand it, it should produce a low pressure (high depression) at idle, and virtually none at wide open throttle. Which mine seems to do. I think mine works most of the time, and just goes nuts every now and then.

[giannispolo]

thanx mate 4 the info

[Polo_Gio]

Hey i need to clean my sensor but looking at it am unsure how to take it out. do the screws on either side secure it and are they the only parts?

Thanks

[JWC]

Yes, but the probe goes in quite a way.

[Polo_Gio]

Is there enough room to withdraw it and the probe then if working with the bonnet open?

Also what did you clean it with and where can i buy it?

Sorry for all the questions,

[JWC]

yeah, its the dip stick that gets in the way.

I cleaned it with WD40!

Didn't solve the problem though!