eternal981

i'm about to just skip my IAC and let the throttle body control the idle... my cars idle likes to hang. driving along, hit the clutch and come to a stop, and the RPMs jump to about 2000, then down to 1500, then to idle. it takes about 10 seconds to finally get to idle. when it's actually idling, it idles fine. steady as i could ask for. but it hangs like no other, and it's sorta embarassing to have the car idling at 2000+ rpms at a stop light.

What could be causing this? I thought it was a bad IAC, so I bought a new one, and actually the new one has made the car hang at 2000rpms longer than the original. Help me out please, this is driving me CRAZY!!

In case it matters, the car is a 2000 Saleen S281, 4.6L V8 with forged internals and new block, ati procharger at 12psi, ported heads, long tube headers, offroad h pipe and borla catback

mustang_montana

ive been having the same problem with mine. basically got a real similar setup to you. i replaced the iac, smoothed things out but still idle hang. replaced the maf, no difference. checked for vac leaks, nothing. checked for and inlet leaks, nothing. basically im convinced it just needs to be tuned right, and ill find out saturday when i hit the dyno. i also got a new egr valve i want to put in. my idle hang got a little worse after the plenum/tb install though. i adjusted the screw due to vac lock i was having, but everything else seems fine.

Rusmisel01GT

Check too see if anything got knocked loose somehow from the intake, check to see if the filter is loose or the pipe going to the filter to the TB... other then that do what montana said.

monkeydude3

yeah i don't have that problem and haven't heard of it happening too much with N/A cars... probably in the tune, because I believe you can set the idle and stuff too


it sounds to me like even tho your blower isn't really in boost, it still is pushing some air in through the intake and the computer is compensating with more fuel which results in higher idle for a bit until it figures out what's goin on

mustang_montana

its rediculously common. almost everyone has the idle hang at some point, well unless they stay stock. im praying the tuner can fix mine. if not then im ripping apart every vacuum line/intake component until i figure it out.

monkeydude3

you know an easy way to find a vacuum leak, is remove the vacuum line where it meets the intake manifold and plug it, do this one by one and if it gets better at any line, you found the 'circuit' the leak is in

eternal981

well I've gotten to the point where if I don't figure it out soon, I'm going to route a toggle switch to the console somewhere to switch off the IAC. I was going to just unplug it and set idle with the throttle body screw, but I can see where there are SOME advantages to having the computer control it (startup, maybe while a/c is running, etc). but other than that, having your car idle at 2000+ rpms at a stop light is about as cool as having your doors painted a different color than the rest of the car.

montana, let me know what you find out! my nearest GOOD tuner is about 2 hours from here (alternative auto, and livernois are both here in Michigan but a decent drive). I've been avoiding going to them for fear that they don't fix the problem, and I have to drive it there AGAIN. if I keep taking time off work to fix the car, pretty quick I can't afford it. haha. talk about being between a rock and a hard spot. how many PSI are you running on your blower? and while i'm at it, what bypass valve are you using to control it? i need to replace my bypass valve for the blower too, and can't decide which route to go.