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Initially I thought this was located in the throttle body, but looking at the SSP PDF it sounds like the maybe the MAF sensor is actually a combined MAF/IAT sensor unit.

Anyone here know for sure?

This is normally the case, and pretty sure if you remove the MAF you'll see it, it's just a resister positioned in the airflow.

Why do you ask?

Teutonic Tuner wrote:This is normally the case, and pretty sure if you remove the MAF you'll see it, it's just a resister positioned in the airflow.

Why do you ask?

I'm trying to find optimum placement for a water meth injection jet. Having a combined MAF/IAT sensor will be a pita really as ideally I think I want to inject after the MAF (so as not to damage/short it) but before IAT sensor so the ECU can advance timing etc based on the cooler air. I've got the Revolution carbon intake which means space is at a premium too.

It should be fairly simple to bypass the thermistor on the MAF with a dedicated inlet temp sensor I did this on my previous E46 M3 as they suffered heat soak where the MAF was positioned. Evolve Automotive produced a kit to do this which consisted of a IAT sensor from an E36 M3 (which was the same resistance as the one in the MAF) and connecting it to the 2 wires from the MAF (cutting just one of them). It worked treat. If you want some more info I can dig out some sketches etc to help you on your way, let me know.

Teutonic Tuner wrote:It should be fairly simple to bypass the thermistor on the MAF with a dedicated inlet temp sensor I did this on my previous E46 M3 as they suffered heat soak where the MAF was positioned. Evolve Automotive produced a kit to do this which consisted of a IAT sensor from an E36 M3 (which was the same resistance as the one in the MAF) and connecting it to the 2 wires from the MAF (cutting just one of them). It worked treat. If you want some more info I can dig out some sketches etc to help you on your way, let me know.

I'm thinking that might be what I have to do - splice the MAF wires and add a separate IAT sensor. Really struggling to find specs of the OEM MAF/IAT though.

Yeah, any diagrams etc would be useful as well as some info on the oem unit in the rs4 if you have it

Here’s a thread (not my thread, but I contributed) giving good detailed pics and diagrams on what to do on the M3. The Thermistor on the M3 MAF was 2500ohms (not sure which temp this is measured at though to give 2500ohm reading, maybe it's 0degC?) which was the same as the IAT sensor on the E36. It maybe that the RS4 has the same value of thermistor so the E36 IAT sensor might be all you need. Imagine that, a BMW part on an Audi...

http://forums.m3cutters.co.uk/showthread.php?t=40600

Teutonic Tuner wrote:Here’s a thread (not my thread, but I contributed) giving good detailed pics and diagrams on what to do on the M3. The Thermistor on the M3 MAF was 2500ohms (not sure which temp this is measured at though to give 2500ohm reading, maybe it's 0degC?) which was the same as the IAT sensor on the E36. It maybe that the RS4 has the same value of thermistor so the E36 IAT sensor might be all you need. Imagine that, a BMW part on an Audi...

http://forums.m3cutters.co.uk/showthread.php?t=40600

Thanks for this. I can probably do some probing with my multimeter and a hairdryer to find out which wires are which.

If I can't find out the specs to enable me to buy a separate sensor, I'll probably buy a second maf sensor and use one for maf readings and one for iat. This water meth project *may* be getting a bit out of hand!

Your welcome. I'm hoping I haven't started you on the road to ruin...

Tony, well done for trying something new again! What sort of gains do you think you might get from this?

MikeFish wrote:Tony, well done for trying something new again! What sort of gains do you think you might get from this?

I'm not expecting huge gains in hp, probably a bit of a kick when it comes in. Also, it feels wrong to spend hours doing backbreaking work (or paying unit20) to do a carbon clean without trying to fix the cause

It's turning out to be quite complicated due to the lack of technical information available from Bosch/Audi on things like fuel injectors and sensors.

Getting some good helpful guidance from Richard at Aquamist, sounds like he's been doing water meth on race cars for years so really knows his stuff.

Once I've made some progress I'll do a proper write-up. I have a feeling it's going to be a pretty cost effective mod once I've done some groundwork.

Bit of an update here and for posterity, the IAT sensor thermistor is definitely combined in the MAF housing. Looks like it's pins 2 and 3 from the left (edit: still testing) having played about with multimeter and chiller spray.

I bought a separate IAT sensor (from a passat I think part number 058 905 379) and it seems to give the same readings as the one in the RS4 maf, so the plan is to rewire and relocate the IAT to just before the throttle body, move the MAF to just after my revolution/pipercross filter (probably with some sort of air straightener to reduce any turbulence) and then place the water meth injectors straight after the MAF. That way there's no risk of shorting out the MAF with mist, gives more space for the water meth to atomise and mix with intake air before hitting the IAT and entering throttle body.

Gratuitous ascii art...