Q for Master Craig :)


New Member
Craig, I have been having idle problems with my 83lb/hr injectors in my '98 Cobra (DOHC 5.4L). The car was initially tuned by Randy@True Blue Performance out in Raleigh, but after a wideband O2 went bad, it started to run like crap. I replaced the sensor along with the install disk, and it runs better but with a surge and extremely rich (even though the A/F reads 13:1). Any ideas? BTW - I'm in South Carolina right now and there are NO tuners nearby! Even Randy is 4hrs from here. Thanks!
Are you idling in closed loop? I get that impression... take it out of closed loop at idle and I wouldn't be surprised if it fixes that problem. Big injectors, closed loop, and idling are three things that don't go together, IMO.

Where would you set the closed loop HI/LOW RPM on a car like his with a 850RPM idle?
Tough to say from here... depends on what makes it "happy", know what I mean? I'd try 1500 for the high and 1200 for the low as a starting point.

Thanks for the quick response! My high/low is already set at 1800/1200 respectively. It tends to idle ok sometimes, but it does one big initial surge (sounding like a throttle follower issue almost) and then tries to idle...

1. Are the IAC settings (pterm/dterm) universal for most cars? What would be a good baseline for someone like me?

2. How open should my throttle screw be?

3. I noticed my battery voltage reads 13.5-13.7 with the car running (12.1 with it on/not running) - is this normal? I thought 14.4-14.5 was normal.

4. My fuel pump voltage varies. On startup, it was 11.7, 10 minutes later, it was 12.2 - is that normal?

Thank you so much. I called "Mike" @ FAST and I did not get much help unfortunately. He actually told me there was no Windows version of C-Com. :(
1. Nothing universal about the IAC P and D terms. the only thing about them that I would say is universal is an approach to getting them set. My advice is to raise them both until it causes idle surging and then back it off a little bit from there. Basically, get the values as high as possible before you cross the point which is obviously "too high." There is a good explanation of what these terms are and how they work in the idle speed section of the help files within the Windows version of C-Com. If you don't have the Windows version, the help files are available on the FAST website. There is a post on this board from a few weeks ago that I put up called "Online help for FAST users" with a link to the help files.

2. The same section of the help files mentioned above will also detail the procedure I recommend for setting the throttle blades.

3. 13.7 or so is normal. It takes a pretty big alternator to get much higher than that. I could get about 14 even with my 140 amp alternator I used to use. That was also with a big electric fan and water pump drive which dropped the voltage quite a bit.

4. Are you sure the battery voltage itself isn't varying? This isn't at all uncommon, due to the extreme stress that starting a car places on the battery. However, you probably want your pump voltage to be constant. Varying pump voltage can throw you for quite a loop if it affects the pressure at all. You may need to run larger wire to the pump if this continues to be a problem.

Thanks Craig - I will mess with the P/D Term on the IAC, but it seems to idle ok sometimes, and other times it acts up. I think my pump voltage is changing. A bigger gauge wire (numerically smaller) to the pump should fix this? I will try it. Thanks again.