Have to let idle for 2 mins or hangs rpm Looking for some ideas here. Did a Head and cam swap on my 2002 Trans Am LS1. I'm data logging my test drives to my tuner. But we seem to have a little issue with Idle. Everything else is perfect. EVERYTIME I start the car I have to let it idle for 2 mins, or I will get the cruise control effect and hanging rpm. And once it starts to hang it WILL NOT go away unless, I cut the car off, restart the engine, and let it idle for the 2 mins. Part 2 to the problem is if I start it with A/C off, I can not turn A/C on. Because it will do the same thing and will not go away, without a restart, or turn A/C back off. I either have to start it with A/C on or off. I cant switch once I start the car or it will start to hang. Tuner is pretty dang good and is trying hard (several adjustment too idle stuff but luck), but he is not local, so its kinda a disconnect, if there is a hard fault. Because I think we are both wondering, if there is more too it then the tune now. I have changed out my TB with a spare, Clean the TB and IAC good, I swap IAC with a spare I had. Same TPS. Random codes, start up with A/C on I have got TCS Off 5 times, ABS 1, and MAP DTC 3 times. It has thrown a TPS and IAC DTC twice. But haven't lately. Mod list: LS1, CNC Ported 799, .625 lift/109 LCA, #42 injectors, LS6 intake, LT, ORY, Dual Dual |
Also saying all that. I have about 500 miles on this setup and ALOT of start ups. So the codes being thrown isn't that often |
Often "cruise control effect" is from a vacuum leak that IAC_counts=0 can't do anything about. That's question #1 - when "hung" is IAC trying to go to zero (and is idle closed loop RPM control active, or defeated, is Q#2). What happens at t=2 minutes? AIR pump shutoff? Just happen to get back to closed loop idle RPM at that time? Weird A/C behavior (esp. refusing to engage at idle) may be an artifact of the tune. Turning off "stall saver strategies" could show whether this is that kind of mental problem (fixing it may want more idle tuning for stability). A/C does bump desired airflow and maybe somewhere along the line, something kooky bistable has gotten into that mess (a long chain from air temp to bump torque to desired air mass to desired airflow, there's some tables that might be bad news if munged). Might put an eye on A/C system pressures and see if you have low side underpressure or high side over- pressure that's messing with you. Wouls not expect this to have a fixed time-signature but maybe it's just a coincidence that behaves roughly the same way when it happens. |
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