ITRCA

If I have been driving and I come to a red light, or some place where I have to stop.. The car idles up at like 1500rpm for about 10-15 seconds.. after that it drops down to normal.. What could be causing that? It's pretty damn annoying at times.

Normal, all of the ITRs do it, including mine.

Completely normal.

Actually thats not quite tru, and it's not normal.

I'm not sure why yours does it, but it's ussualy if you've messed with either your TPS, or you IAC.

I actually switched to OBD1, which has caused a whole world of problems with my idle, but before I switched recently, when I was using my stock ECU, or when I switch back, nothing like that happens, if I drop the clutch it always goes back to about 850 rpms regardless of how I was driving. Out of all the ITRs I've driven at the shop. I've never noticed that any of them do it.......Not saying that none of them have, I just figure that would be one of those more noticable things, as you said, it would be pretty annoying.

If it's still under warranty, take it back to the dealer, and they'll hook it up to the computer, and make sure all the readouts, are with in the specified parameters.

Good luck......

Could be worse mine fluctuates idle after it has been run hard. then stabilizes.

OH! The five Rs I have been in all do the idle thing then rest at 850-900.
go figure some do some don't.

My ITR idles around 1500 RPM when started on a cold engine, but after it's all warmed up, it likes to sit around 900 RPM. However, if you sit there and turn your steering wheel this way and that, it kind drops a bit (same as if you turn on your A/C). But I've never heard of stopping at a stop light, and having it raise up, and then drop.

FBP ITR#00-0202 wrote:If I have been driving and I come to a red light, or some place where I have to stop.. The car idles up at like 1500rpm for about 10-15 seconds.. after that it drops down to normal.. What could be causing that? It's pretty damn annoying at times.

happens to me also. i think it idles higher when the fan turns on.

I believe the reason for this is emissions related. The idle is kept high while leaning out the fuel mixture to lower emission. When the throttle blade slam shut, the fuel mxture is still very rich. This is checked during a smog test. Here in Massachusetts, the cars are accelerated on a dyno at a certain rate to 30 MPH. At 30 MPH, the gas is released, thus closing the throttle blades and causing the emissions to go up. If you don't let the car idle down, you won't get that spike in emissions. This is the way car manufacturers get around smog tests. Car pollute worst at idle.

ok, this isn't like some life or death for my car question, but i am curious. start your car (cold motor, might work warm, but never tried it). Sit there and watch your RPM on your tach. While still on a cold motor, turn the steering wheel this way and that. as you turn it, did you notice your rpm drop, and hear the valves reset? when you stopped turning it, did your rpm go back to normal warming range? why does it do this? (leave your E-Brake up, so you're not moving, of course).

If your engine is cold, the power steering fluid is much thicker than when it is warm. The power steering pump has to work quite a bit harder too move the thicker fluid. 4 cylinder engines don't make a hell of a lot of torque a idle, therefore any extra temporary loading will cause the idle to drop until the loading is dropped or the IACV compensates for the additionalengine load.

In otherwords in english that means that, when your sitting at idle, your motor needs to strugle to push all your accesories. Although, I don't think your power steering fluid really thins out that much. In any case, your car really doesn't have as much power to run your alternator, so all the parasitic drag off your power steering, basically steels all the belt speed used to push your alternator, therefor, your not getting as much power to run your motor, it's almost like running on an almost dead battery.

And actually on a side note, even once your car is warm, turning the wheel while standing still will affect your idle, but generaly in the opposite way, your IAC will bump your idle up a couple hundred to compensate for the extra load. This same thing will happen if you pump your brakes a couple times while sitting still as well.

Later......

Actually, pumping your brake pedal several times causes a drop in intake manifold vaccum. That causes the fuel injection to compensate for momentary low engine vaccum, thus raising idle speed.

thank you everyone, that was very informative...now i know why when i raced on a cold motor i lost to an si (we've all done stupid things before...right? )

00ITR#756 wrote:pumping your brake pedal several times causes a drop in intake manifold vaccum.

Sounds like an interesting theory........why???

Power assisted brakes require engine vaccum which is stored in the brake booster. Eveverytime you step on the brakes, you cause a drop in engine vaccum utilized by the brake booster.

Kool, never knew that

Thanx....

I never thought about that occurance being emissions related. My friend had a 95 Mustang 5.0GT and his car would hang between shifts (the revs wouldn't drop off) and this was to burn off emissions between shifts. This has turned out to be a very informative thread! Thanks everyone.