Ambient air temp sensor

[stevo]

Hello Everybody, I have been trying to track down an intermittent problem which involves lose of power from a low idle to about around 1700 RPM then comes back to life, what I have found is when the ambient air temp reads 119-120 degrees this is when it goes into limp mode, also noticed the temps can drop to -30 and everything in between then settles to where you would expect it to sit.

I thought the sensor was on the top half of the air filter box and would have thought unplugging it would give me a Zero reading but continues to show a reading, disconnected the Maf sensor and the air flow drops to 0 my car is a 1999 TD5 and have had it since new, it is a pain as sometimes happens at traffic lights.

Sometimes can go days without playing up then can play up multiple times in a day, but not when cold only after everything has warmed up.

Any help would be much appreciated and would be the 1st time a sensor has played up, the sensor in the air box is not cheap either so do not want to replace the wrong one (Fault has been there a few years but has gotten worse lately).

[Graeme]

Have you checked the wiring that runs across the front of the head? The covering deteriorates which then allows the wires to rub on metal eventually wearing through the insulation.

[SPROVER]

Have you checked for oil in the loom at the ecu?

[stevo]

I fixed the wiring years ago and covered it in heat proof conduit the only wire that i did find stuffed was the oil sensor wire, also my loom has been dry for years after doing a couple of mods have never had oil show up at the ECU, would like to find where the sensor is positioned then disconnect it and see what the reading does then.

[discorevy]

assume you mean the Intake air temp / boost sensor , try removing it, clean with contact cleaner and refit.
( it's located in the middle of the intake , 2x 8mm head bolts )
you may have to replace if cleaning doesn't work.

[Graeme]

The ambient air temp is indeed the one in the airbox. When disconnected a default value is used which from memory is quite low for our climate.

[shack]

The so called "Ambient temp sensor" is indeed the airbox lid.

The intake temp sensor is in the inlet manifold under the engine cover- if still fitted.

Both will cause issues if misreading.

If the temperature is still jumping around after being unplugged, it will be wiring or ecu issue.

Note that they both have default readings if they play up.

I'd say from your temp reading, it's the sensor in the manifold.

Cheers
James

[discorevy]

If Stevo's is eu2 there won't be an ambient air temp sensor in the airbox lid.
The fact that he is able to read the temps points to intake air temp sensor or related circuit

[shack]

If Stevo's is eu2 there won't be an ambient air temp sensor in the airbox lid.
The fact that he is able to read the temps points to intake air temp sensor or related circuitGood catch! Can't believe I missed that.

But yeah, the IAT defaults to 120° from memory.

[stevo]

With a cold engine and disconnecting the sensor on Manifold reading went straight to the default of 199.4 weird thing was when I disconnected that sensor with a Hot engine I was still getting a reading that varied so will have to dig further.

Did check oil at ECU but was Dry as did some Mods about 15 years ago that seems to have stopped the oil getting to the ECU.

[shack]

Ok,

I'll have to recheck my figures, but that sounds wrong.

I'll see if I can do something tonight, I realize it would be frustrating.

Cheers
James

[Bazzle218]

I would be givng the ECU plug / socket a clean the red one looks oil contaminated.

[stevo]

plugs all good just discolored with age and grim, now after having a further play and seeing what things were doing and when it pointed back to the sensor only with a warm engine and more likely to play up after sitting at lights for a period of time or parked up after a run so heat would build up in manifold, replaced it and all is good when sitting at traffic temp will climb slowly to around 40 degrees but everything stay steady with readings no more jumping around.

So if you have an engine that just goes gutless till about 1500-1700 RPM then takes off this is another thing to check and after 22 years this is the first sensor to fail on the car.

Part number is MHK100640 or the Bosch number is 0 281 002 205.

[discorevy]

you're welcome [thumbsupbig]

[AK83]

Just question re AATs, and more specifically TD5 airbox covers.

Mine is an 02(I'm pretty sure EU3).
One day at pick-a-part .. I found a half stripped TD5. Idiot me didn't bother to check the plate or VIN for year, but the airbox cover was in good nic, so I grabbed it.
In mine, some 'gorilla hack' has busted it up and it needs a tek screws for one corner and the clip for the other side, so is not sealing perfectly. It's not bad, just not right.
No way I'd take it into a river crossing tho!

Anyhow, the AATs are different.
I could use the good lid I got, but the sensors are differently plugged and sized so don't fit. ... arghhh!

Anyone know of differences in AAT types? I can't seem to find any info.

The sensor in each air box lid fit perfectly in their respective spots, but IIRC the one form the wrecker has smaller spacing for the screws and I think one less pin on the plug.

I'll have to get some photos up I reckon.

[shack]

If it's 4 wire it's EU3. AAT + AAP

If it's 3 wire it's EU2. AAP only

They read differently to each other and aren't really interchangeable, certainly not a good idea to put an EU2 on an EU3 engine.

But you shouldn't be able to plug the wrong one in, different plugs.

And it's a long time since I looked at a Nanocom, but I don't think they report ambient temp, only ambient pressure..is that what you are referring too?

[AK83]

If it's 4 wire it's EU3. AAT + AAP

If it's 3 wire it's EU2. AAP only

They read differently to each other and aren't really interchangeable, certainly not a good idea to put an EU2 on an EU3 engine.

But you shouldn't be able to plug the wrong one in, different plugs.

And it's a long time since I looked at a Nanocom, but I don't think they report ambient temp, only ambient pressure..is that what you are referring too?

definitely the AAT.
I knew there was a one wire difference and the plugs don't fit and the sensor is differently shaped and sized and that the airbox lid also has difference to make them not interchangeable .. etc. [biggrin]

... ok, so I got to source another airbox lid too ... [thumbsupbig]