When I tried to add these pics to the n00b’s guide on MAF cleaning, it said there were too many pics. So, it gets a thread all by itself.
When you clean the MAF, you should “reset” the Engine Control Unit (ECU) to put it through a “re-learning” process. You should do this when you clean the air filter, MAF, get new O2 sensors, spark plugs, injectors, a CAI, or exhaust and/or cat back system. Anything that affects the motor.
What you’ll need:
A Spyder! (year and color vary)
The engine should be cool when you perform this procedure, or you are likely to get burned.
–and a 10 mm wrench if you’re going to remove the negative battery terminal clamp.
You have 2 options: 1) remove the ECU fuse for 20+ minutes (preferred); or 2) remove the negative battery terminal for 20+ minutes. Although less time might be required for reset, it seems that 20+ minutes is the common method. For best results, remove the terminal or ECU fuse before you clean the MAF (or do whatever you’re doing to the car that necessitates the reset).
OPTION 1 (PREFERRED): Removing the ECU fuse. This method has less “collateral damage”–it will not lead to the loss of your radio presets or clock setting.
Where is it? It’s in the fuse box on the forward driver’s side portion of the engine bay, next to the battery.
There’s a small ‘catch’ on the front (frunk side) of the fuse box cover–push it in with your finger and lift up on that end of the cover. The cover will lift off. The rear catches are like hinges, so you pivot the cover and it will disengage from that side.
When you lift the cover off, it will be ‘upside down’–turn it 180 degrees so the diagram on the inside of the cover matches up with the fuses.
Examining the fuse diagram on the fuse box inside cover, you’ll see the ECU fuse as the 2nd one from the bottom on the left side (in the third slot–the lowest slot is empty in a stock Spyder). In this photo, the ECU fuse is outlined in blue boxes on the cover diagram and the fuse box itself. In the rear right corner of the box, there is a pair of plastic fuse pullers (they look like plastic tweezers) designed to safely remove the fuses (yellow arrow).
Remove the fuse pullers, squeeze the top together to separate the forks, and lower the forks over the fuse. Relax your grip on the top, and let the fuse pullers grasp the fuse. They will click into place.
Pull up gently on the fuse pullers (but don’t squeeze the top together, or they will let go of the fuse) to remove the ECU fuse. 
Here is a view of the fuse box from the driver’s side of the car, with the ECU fuse removed.
Put it in a safe place.
Leave the fuse out for at least 20 minutes for the “reset” procedure.
To reinsert the fuse, use the fuse pullers to gently reinsert it into its proper receptacle. NOTE: the numbers on the top of the fuse will be upside down to you when inserted correctly (look at all of the fuses–the numbers face opposite your direction). Make sure you put it back in the same direction you removed it. It will click into place.
Release the fuse pullers’ grip on the fuse by pinching the top together and pulling upward. Put the fuse pullers back in their place.
Replace the cover by turning it back around (so the diagram is now upside down to you), hook the two catches on the rear end on the ‘hinges,’ and push down on the front of the cover until it clicks into place.
OPTION 2: Removing the NEGATIVE battery terminal clamp.
**NOTE: this will result in the loss of your radio presets and clock setting.
The battery is on the driver’s side of the engine bay. Here’s a hint–the positive battery terminal is the one with the red cover with the big PLUS sign on it.
Using a 10mm wrench, loosen (but do not remove) the nut on the negative terminal clamp.
When the clamp is sufficiently loose, grasp both sides of the clamp. Wiggle it back and forth and pull up gently, and it will come off the terminal.
To protect the terminal clamp while you work on other things (like the MAF sensor cleaning), you can wrap it in a cloth.
Leave the terminal disconnected for 20 minutes. To reconnect, simply place the terminal clamp back over the battery terminal and gently push it downward until it is firmly seated on the terminal. Using the 10 mm wrench, tighten the nut so the terminal clamp is firmly secured. If you have an SMT, you may hear the accumulator pump start up when you reconnect the terminal–it can be startling, so just be prepared.
So, now that THAT’S done, let’s move on to the nitty gritty. You can clean the MAF while the ECU fuse or battery terminal clamp is disconnected, to make the most efficient use of your time. See the separate page for cleaning the MAF.
This documentation in no way replaces the Toyota MR2 Repair Manuals. The purpose of this content is only to provide supplementary information to fellow MR2 enthusiasts. Midship Runabout and its contributing authors will not be held responsible for any injury or damages that may occur as the result of practicing any of the methods or procedures described within this website. Article and photo submissions are property of the contributing author.
