Dave recently sent me this question, I thought I would answer it in a thread as I think this is a popular topic at the moment and there might be more people who have similar or related questions. There may also be other people who have opinions and experience to share to help everyone get a balanced view of the topic.
"I have the apexi power fc, Is it possible to map myself or is it best to get TDP to do it, and if its best to get tdp to do it then is it much point having the Apexi in the first place or does it just help them map it better etc, My car was running very rich so i'm looking at getting it mapped"
My view on it:
It is possible to do a DIY mapping session, that is the beauty of the PowerFC (and any standalone ECU). The PowerFC is regarded as somewhat of a 'simplified standalone' in that it has just enough to be programmable, without having so much that you need a computer science PhD to understand it. For that reason it is a good ECU for novice mappers. If you are chasing ultimate power, then DIY or 'street mapping' is not a very good choice as there are not very accurate tools available for determining if the changes that you are making are having a beneficial or detrimental effect on the performance of your car. You can buy
GTechGtech meters etc, however changes due to windspeed, road environmentals, traffic conditions etc mean that you only have a very rough measurement to consider and from one day to the next your results can vary. They are fun to play with though!
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Regarding DIY mapping, the elements that you need to take in to account for when mapping are:
* Air/Fuel ratio
* Ignition timing
* Correction factors
Air/Fuel ratio
You may have heard that your engine is essentially an air pump. The pumping action is created by burning air and the more air you can burn, the more torque/power your engine creates. There can be many catalysts (fuels) for burning air, the one most people are familiar with is unleaded petrol (however e85 is also used in Ireland).
As with anything, there is a balance point where you want to have a good mix of air and fuel to burn. If you have too many parts of fuel in your Air/Fuel mix, your engine will run "rich" meaning smokey, chugging, poor pickup, clogging up spark plugs etc and overall be down on power. If you have not enough parts of fuel, you will get "lean burning" which normally entails higher temperatures, down on power, and at the extreme end, damage to your engine. There is a Stoich point, which essentially means the balance point of not too rich, and not too lean. There's a whole science behind it but in general for unleaded you find this point around 14.7:1 at idle. That is 14.7 parts of air (measured by weight) to 1 part of fuel.
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Note that this is at idle and cruise and not the AFR to use when aiming for maximum power in a turbo or NA car. I am led to believe that in general these are 11.5:1 (turbo) and 13.0:1 (NA) however as stated previously it is only through dyno tuning that you can get an exact understanding of where optimum performance is.
So as you can appreciate, changing the AFR that your engine runs at can make things worse or better, and you need to be able to tell if your adjustments are heading in the right direction. Your MR2 does not have an AFR sensor that is accurate enough to detect these readings from the factory. There is a factory O2 sensor that does this job, however it is what is known as a 'narrow band' sensor, meaning that it can only detect for vary minor changes in the state (i.e. it says to the ECU - I am rich, or I am lean, it will not say by how much, or what the measurement is)
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To be able to tune effectively, you need to have a much more clear view of what the AFR is that your engine is running at. This is achieved through using an aftermarket "Wideband Sensor" which can be installed in to your downpipe or exhaust system (this may require a bung to be welded in place or you can get adaptor plates for the factory location).
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Two popular options for wideband kits are the Zeitronix ZT2 (http://www.zeitronix.com/Products/zt2/zt2.htm) and also the LM1 from Innovate (http://www.innovatemotorsports.com/products/lm1.php) both of which do a similar job but have various functions and features to differentiate themselves.
Using a wideband, it is possible therefore to adjust your fueling at different points while the engine is running to get to a desired outcome. The dyno tuning companies use the same tool to do the job, however because they can measure changes in power at the wheels, they can be more accurate at getting your fueling mix right.
The PowerFC allows for changes to the fueling correction map straight from the hand commander.
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Unfortunately however, the screen is very small and you can not see the whole map at once, this would not put off a serious tuner who knows where to look, but as a novice I preferred to look at the map on a laptop so you can see the whole map at once. One problem with this however is that the PowerFC (from the factory) does not allow you to connect a laptop unless you are an APEXi dealer (boo), so some clever chaps in New Zealand (Gidday Gil!) decided they would invent a black box that connects to the PowerFC and allow it to be programmed (this is called a Datalogit and is available at: http://www.fc-datalogit.co.nz/)
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The Datalogit comes with software called (FCEdit) which allows you to edit the relevant tables within the PowerFC and directly adjust fueling/ignition timing etc. There are other software packages written to work with the Datalogit (eg: Co-pilot by MR2 owner and genius Kevin Bean) however I have not used them first hand as yet.
This is what a fueling map looks like in FCEdit. The points on the left hand (vertical column) are load points (i.e. how hard you put your foot down, or if your car is going up or down a hill) and the points on the top horizontal column are RPM.
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Examples:
My car idles around the cells 5000(V) and 1200(H).
When accelerating hard in first gear I am using cells 3000-12000(v)
When accelerating hard in third gear I am using cells 10000-20000(v) etc
Summary
Just to re-iterate, yes it is possible to DIY map although you need to get hold of the right equipment to do so. You won't get maximum performance out of your car but you will have a lot of fun getting it 95% right and learn a lot in the process. You will also be able to cut down on dyno tuning time as the professional tuner will probably only need to tweak some stuff rather than do a whole map from scratch.
It's cheaper to just go to a dyno and pay the money, but is that really fulfilling for a hobby? I guess it's down to the individual.
There's a whole other side to mapping which includes ignition timing (equally if not more important than fuel), I've written some threads last year on 3sgte tuning and ZT2 installation that go over fueling and timing:
http://www.mr2.ie/index.php/mr2-forum/8-performance-and-repairs/91-3sgte-tuning#137
http://www.mr2.ie/index.php?option=com_kunena&Itemid=53&func=view&id=554&catid=18#554
Please feel free to ask more questions/discuss/add other opinions or items and let's discuss. I have a lot of screenshots and data that I can add in to explain further details... :)
and I'd say i'll be thinking seriously of getting some hardware & software to get it 95% right further down the line 
Food is obviously thrown out but just need the BBQ utensils. I'll grab them from you at the next meet/mini-meet.
and thought "I should have known utensils wouldnt take up two bags" as I looked in at 
green mouldy sausages, 
