There is a way to solve this promblem go to the dealer have them put on there diagnostic computer on the car and to set the throttle to 1-6 %...this is common for the evos and to check your battery it is not dying on you...Because when the car starts and the battery goes lower then 10 volt on crank the ecu loose postion on the throotle body..and that could be if you have a smaller batt too...I had the same problem and I put a expensive battery on and set the throotle postion and i am ok ...I hope this helps you guys....

 

I have built three evo's before mine that idle perfect. Mine of course does not. Cold start is good but once warm my a/f is anywhere between 10:1 to 12:1. Never has cammed clean like most evos with cams. Just clean, stock sounding idle. The biggest thing that catches my attention is that my AIC valve gets VERY warm with the engine cold and the key in the on position. Strange to me. Also randomly makes ticking noises. The ECU does not respond to flashing when I try to bump idle. When I unplug AIC valve while the car is hot and running it idles good and revs a little bit better, but still pig rich. I think I will try checking voltage at the AIC valve. HEAVLY MODDED.

 

my 2003 evo isn't modified at all aside from exhaust / downpipe, one day i was idling at around 900 (like always) then at the next stop i was idling at 400-500 and dying. it's been that way now for 4 days, i've been using the e-brake and holding the gas to keep it running at stoplights. anyone come up with a solution to this problem?

 

ok, so i turned that phillips screw on the backside of the throttle body.. out about 3 turns and the idle went back up to 900 RPM. i'm sure that's just masking the problem, plus this morning when i started my car it wouldn't stay running until it was warm. at least once it's warm it stays running at stops now.

i think the problem is either..
boost leak or gunky throttle body. i'm hopefully having my throttle body cleaned this week.

 

Turning the phillips screw was not a good idea. The throttle body is calibrated from the factory with that screw set in place. I will check the factory service manual for the proper readings at the AIC valve and post them when i can. Also my evo's readings...

 

It doesn't make a difference really, turning that screw in and out just increases or decreases the amount of air bypassing the throttle plate to raise of lower the idle. On some DSM's I've worked on that's the only way to adjust the idle after using a new SM intake and a different TB. 2003's especially have issues with the AIC valve, the gears like to strip out after a while and idle becomes very erratic. Flashing the ecu with a higher idle rpm should raise it IF the AIC is working properly.

 

great posts, thanks guys!

 

Call the mistu dealer and ask them if they updated your flash.. could have messed a few things up not knowing it has already been tuned.

 

my evo 8 was doing the same thing minus the stalling and trouble code. your coil pack is most likely the culprit as it was with mine. check to see if the coil pack is weak.

 

I took out my plug and found that they were way out of spec. When I tried to close the gaps a bit, the iriduim tip broke on 2 of them.

My car idles like a champ after replacing the plugs and doing the following...

I raised the ISCV tables in the 2 highest heat ranges, raised the lowest idle settings to 1000 RPM on all idle table. I raised base idle timing to 8 degrees in 500 to 1000 RPM and 100 and lower load. Finally, I raised the Idle Sensitivity to 148 from the stock 128 setting.

In addition to all of the above, I also calibrated the MAF for the 75 and below Hz values. As it turns out my HKS suction with K&N required be to lower the values on the MAF scaling table.

Took a lot of work.....but the car runs fantastic.

Oh and I am running the FP green, AMS 780cc injectors (FIC), full HKS hard pipes, Blitz FMIC, APS BOV, and revolvers.

 

matty8 tell ur mech to watch data on his scan tool. needs a decent one like modis or possibly genesys see what iac and maf are at idle ecu should see maf around 5gps and iac somewhere between 20 to 30%

 

How did you did you go about the above? how many points did you end up having to drop the values?

-E

 

The process is rather lengthy.
(do a search for "scaling the MAF"; the thread will tell you all)

My Clif Notes Version.....

Scale your MAF to read Hz then....

1) Varify your injectors are properly scaled with the stock rubber MAF tube. (LTFT all within +/- 3%) (STFT hovering around 0%)
2) Log idle MAF HZ with the stock MAF tube (just to for varification purposes)
3) Log idle MAF HZ with the HKS suction pipe (mine was about 50Hz)
3a) Notice how your injector STFT and LTFT are now off becasue of the HKS pipe
4) Add the total change in the STFT and LTFT in terms of %
5) There is a adder value of 140 so add 140 to the logged idle MAF Hz unit
6) Add or subtract your % from the (adder + MAF Hz unit total)
6a) If the % is + then add to the MAF Scaling.
6b) If the % is - then subtract from the MAF scaling
7) Subtract back out the 140 adder
8) This is your new MAF value

My math....

Logged MAF HZ = 50 50 Hz = 165 MAF Units
LTFT Low = -1%
LTFT Mid = -7%
STFT ~ = -3& avg

165 MAF units + 140 Adder = 305
LTFT Low -1% + LTFT Mid -7% + STFT Avg -3% = -11%
305 - 11% = 271
271 - 140 adder = 131 New MAF units

I then used the same calculation for the values below my idle Hz.

For some of the other values I added or subtracted to make the curve as smooth as possible.

My idle scaling values are....

19 - 114
25 - 120
50 - 131
75 - 167
100 - 180
125 - 187
150 - 191
175 - 195
200 - 198
225 - 201
250 - 203
275 - 206
300 - 208
400 - 216
500 - 222
600 - 227
800 - 233
1000 - 236
1200 - 237
1400 - 235
1600 - 232

 

sorry, but what is the IAC?
Idle Actuator controller?

 

IAC stands for "Idle Air Controller"
at least i think so, some people also call it idle control valve.