IAC and starting question

[v8zcar]

After fixing a clog in my fuel return line which was causing abnormally high fuel pressures, I was unable to start the engine unless I held the TB plates open the a little.

After the engine revs up and continues to run, I can let go of the TB lever and bring it back to full-closed without killing the engine.

When the engine is running, I watched various screens for IAC position and TPS and IAC vs CTS. Moving the line on the Throttle Follower screen, Start IAC Pos vs CTS screen, and Idle Speed vs CTS screen doesn't have any "real time" effect on how the engine runs.

Is there anyway to test the IAC's actual movement?

Thanks,
Owen

 

[Craig Smith]

Not without removing it and watching it slide back and forth. An IAC motor doesn't provide feedback as to what it is doing. The computer can only tell it where to go and assume it does it.

What kind of target numbers are you seeing? I'm gonna guess that they are high and often pegged at 180. Is this the case?

If so, you have about 2 minutes' worth of work ahead of you to correct the problem. Are you up for it?

 

[TwinTurboIroc]

LOL, craig is in a good mood

 

[v8zcar]

Hope he's still in a good mood from yesterday! I'm all ears!

My target numbers were around 55, don't remember off hand but not pegged real high.

The reason I asked as that I can't start the engine without opening the TB plates, but then the idle is real high. But then I can't bring idle speed down when I try different IAC settings. My guess is I should have a balance between IAC opening and TB opening, right?

Thanks,
Owen

 

[TurboTR]

Yes. If you can't adjust idle with the IAC then the TB is probably out of whack and the IAC is out of control range, pegged either high or low. The throttle blade still has to be adjusted properly for it all to work right.

TurboTR

 

[tazgn]

I had this exact same problem today as I loaded a new program in the car I was tinkering with. But for me it was the cranking vs revs table I screwed with and caused it. Also the IAC P and D terms. I got it worked out now. But there seems to be alot more than jus tthe target IAC involved in the starting sequence to keep the motor running. (My new VE numbers down at idle were a bit off too). Just sharing my frustrating experience today with you.

Derrick