Strange behavior when cold (just started)
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Joined: Sep 2002
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From: LI, NY
Car: 88 GTA
Engine: 305 LB9
Transmission: T5
Strange behavior when cold (just started)
Folks,
88 GTA, 305 5.0 TPI, stock
Did a search, couldn't find what I need. It's minor thing (if there is such an animal), but when I first start the car, if I blip the throttle, there is no rev at all. It seems as the engine gulps the air but doesn't get any fuel. It feels like it wants to stall (just for a split second). If I lay off, the car idles fine and once I start driving, the problem goes away, and stays away.
The car has the cold start valve in the driverside runner. Is this a normal sympton? IAC? O2 sensor? Plugs, wires, cap, rotor, coil are all new. Car is timed to 6* (as per hood sticker) and idles and runs fine other than this issue at start up. Thanks.
Kevin
88 GTA, 305 5.0 TPI, stock
Did a search, couldn't find what I need. It's minor thing (if there is such an animal), but when I first start the car, if I blip the throttle, there is no rev at all. It seems as the engine gulps the air but doesn't get any fuel. It feels like it wants to stall (just for a split second). If I lay off, the car idles fine and once I start driving, the problem goes away, and stays away.
The car has the cold start valve in the driverside runner. Is this a normal sympton? IAC? O2 sensor? Plugs, wires, cap, rotor, coil are all new. Car is timed to 6* (as per hood sticker) and idles and runs fine other than this issue at start up. Thanks.
Kevin
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GTA,
Your symptoms should really have nothing to do with the cold start injector (valve). It is only active during cranking, and for a moment or two afterward. Once the engine is running, it becomes useless and inconsequential.
Hesitation on throttle tip-in is a common situation when the IAC is open wide to maintain a higher RPM. The throttle body is essentially in a high bypass mode, whereby most intake air is routed around the throttle plates. The air on either side of the throttle is stagnant, or basically not moving. This can be counteracted to some extent by resetting the minimum air position of the throttles so that the base RPM is on the high end of the allowable range. This makes some air flow around the throttle plates at all times and minimizes that "dead air" syndrome. As long as the throttle body and IAC are clean and in good working order, the ECM should still be able to control the engine RPM at the target idle.
You'll never completely eliminate the tip-in hesitation, but can minimize it. The phenonmenon will always be more pronounced when the IAC is opened farther (like on a cold start/high idle).
EDIT: For all you grammaticists, I meant "farther", not "further". There is a subtle difference. I would have typed "further" if that's what I meant - not that I have great keyboarding skills by any means.
Backing up a step or two, why would you want to "blip" the throttle on a cold engine, anyway? The IAC/ECM are in complete control of the RPM, so there is no way to "kick down" the idle. And the extra, unnecessary load on a cold, loose set of bearings is never a good thing. Start the engine, adjust your mirrors, check the gauges and idgit lights, play with the radio, shave, eat breakfast, roll yourself a fatty, put on your seat belt - do whatever it is you do. But wait about a minute or so before you get happy with the throttle. Your engine will appreciate it. Your oil will stay cleaner and last longer, too.
Your symptoms should really have nothing to do with the cold start injector (valve). It is only active during cranking, and for a moment or two afterward. Once the engine is running, it becomes useless and inconsequential.
Hesitation on throttle tip-in is a common situation when the IAC is open wide to maintain a higher RPM. The throttle body is essentially in a high bypass mode, whereby most intake air is routed around the throttle plates. The air on either side of the throttle is stagnant, or basically not moving. This can be counteracted to some extent by resetting the minimum air position of the throttles so that the base RPM is on the high end of the allowable range. This makes some air flow around the throttle plates at all times and minimizes that "dead air" syndrome. As long as the throttle body and IAC are clean and in good working order, the ECM should still be able to control the engine RPM at the target idle.
You'll never completely eliminate the tip-in hesitation, but can minimize it. The phenonmenon will always be more pronounced when the IAC is opened farther (like on a cold start/high idle).
EDIT: For all you grammaticists, I meant "farther", not "further". There is a subtle difference. I would have typed "further" if that's what I meant - not that I have great keyboarding skills by any means.
Backing up a step or two, why would you want to "blip" the throttle on a cold engine, anyway? The IAC/ECM are in complete control of the RPM, so there is no way to "kick down" the idle. And the extra, unnecessary load on a cold, loose set of bearings is never a good thing. Start the engine, adjust your mirrors, check the gauges and idgit lights, play with the radio, shave, eat breakfast, roll yourself a fatty, put on your seat belt - do whatever it is you do. But wait about a minute or so before you get happy with the throttle. Your engine will appreciate it. Your oil will stay cleaner and last longer, too.
Last edited by Vader; Nov 2, 2003 at 08:14 AM.
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From: Palm Bay, Florida, USA
Car: 95 E-150 & 07 Kawasaki ZX-6R
Engine: A slow one & a fast one
Transmission: A bad one & a good one
Axle/Gears: A weak one & a chained one
Vader...All of that is some damn good information...but....
To my experience, 'blipping' the throttle WILL kick the idle down. Granted, it still won't be at a BASE idle, but it will idle lower than previously. My V6 Camaro worked this way, and my V8 Mustang does too. (EFI, stock ECM, new IAC valve). The Mustang will sit and idle at 1400 cold...if I blip it, it'll sit at about 900. On some days I HAVE to flinch the throttle to bring the idle down. Otherwise, the rpms will drop too far too fast and stall the car.
To my experience, 'blipping' the throttle WILL kick the idle down. Granted, it still won't be at a BASE idle, but it will idle lower than previously. My V6 Camaro worked this way, and my V8 Mustang does too. (EFI, stock ECM, new IAC valve). The Mustang will sit and idle at 1400 cold...if I blip it, it'll sit at about 900. On some days I HAVE to flinch the throttle to bring the idle down. Otherwise, the rpms will drop too far too fast and stall the car.
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