Mach2

I have a quick question about the deceleration fuel cut feature on the PFC. What exactly is its' purpose? I read about it on page 33 of the manual, but it doesn't say what it's for. Btw, is there any reason why my car's idle jumps to 2K during cold starts? I clipped the wires, but it still seems to do the AWS. Only thing different is that with the stock ecu I could avoid it by starting the car in gear, and with the PFC that doesn't work and it'll still jump to 2K. I don't have the common fluctuating idle so I don't think it has anything to do with the adjustments. After a while it settles down to 800rpm and stays perfectly. Any input? I searched through all the old posts but didn't find any helpful info. Thanks in advance!

Xcessive

There is an air bleed screw under the throttle body that usually needs
to be turned in approx 1/2 to 1 turn or until the idle goes down.
Factory setting is approx 2 turns out.

FD Racer

also check the screw for the fast idle cam that works with the hot wax rod. The more distance between the hot wax rod and where the screw threads are the less of a high rpm warm up you will get.

adax

iTrader: (2)

As I understand Deaccel. fuel cut, it does the following:

If you notice when you let off the throttle and coast, injector duty cycle goes to zero. The stock ecu maintained fuel to one rotor when coasting under some conditions but I'm not sure if the PFC does this. Obviously if duty cycle remained at zero, the car would eventually die. This setting specifies what RPM fuel is again injected to prevent stalling, and there are settings according to electrical load conditions (see manual). If you have a light flywheel, revs tend to drop faster so you may need to increase the RPM at which the injectors come back on to prevent overshooting (undershooting) the idle RPM.

Alan Cross

Giving it a little gas when costing down with an open exhaust produces the nice GT car-esque burbling and popping.

cewrx7r1

iTrader: (2)

It's purpose is to turn off the injectors during de-acceleration to clean up emissions. At the set point, the injectors are turned back on to prevent the engine from dying and then it goes into idle mode.

Mach2

Thanks for all the replies. The description of the decel fuel cut was exactly what I was looking for. As for the hgh rpm's during cold start, I adjusted the air screw till it was fully closed, and it leveled off the hunting idle. I never adjusted the fast idle cam, but shouldn't it work fine the way it was originally set? It workd fine with the stock ecu. Why would it act up with the PFC? Could it have something to do with the Water Temp correction? Could the settings be too lean for the colder temps, causing the idle to rise? After it warms up the idle levels off at 800rpm. Thanks in advance.

RecKleSs

Mach2...wow, I didn't know you had your car back on the road. As for the idle my car idles around 2000 RPM until it warms up, which is about 58C. The RPM will drop to 850 RPM. This only happens when the car has been sitting for a long time and when it's very cold outside.

Mach2

Jay,
I got it back together a week ago so I'm still taking it nice and easy. Only got 50 miles on the new engine. As for the high idle, I was able to fix that by tightening the screw sitting on the hot wax rod. I tightened it till the idle reached 1500-1600rpm. Now when cold the idle jumps to 1500-1600rpm and slowly levels off to 800rpm. Everything works great now. I don't know why it needed adjusting since I had never touched it, but at least it's fine now. Thanks for all the help!

KZ1

I think a lot of people get anxious and turn down the screw prematurely, from my experience a few days with PFC adn it will correct itself to perfect idel. TO all those with hunting idle just, just drive it will most liely fix itself. For example: after install mine had same fluctuating idle, then smothed out, then used brakes for first time at idle, started to flutcuate again, then smoothed out. WHne fans came on for first time, started to fluctuate, when headlights on first time same thing. after awhile everything is cool, and PFC works liek a champ, I never played with cams or screws, etc.

cewrx7r1

iTrader: (2)

All of this idle fluctuations when using the PFC, even after driving for a while, is the result of how much better it controls fuel and timing at idle than a stock ecu.

The O2 and timing control functions (under ETC) increase idle efficiency so much that the engine is getting too much air that the ISC solenoid can not be closed any more because it is closed all the way. Then the PFC adds more fuel to reduce revs but his then makes the O2 too rich, then it leans it out. These out of bounds conditions that it can't reach causes the cycling effect. That is why most of us have to help the unit by physically reducing idle air by adjusting the air bleed screw and/or idle set screw.

My idle O2 voltage stays around .03V with the air pump working. Very lean and clean. My exhaust tip is light black/darkgray for the first time in 9 years. Before it was very very soothy black. With the pump disconnected for UEGO O2 testing, idle O2 voltage is .8V.