Personal computing discussed
Moderators: askfranklin, renee, emkubed, Captain Ned
anonymous38 wrote:I have a 2003 pontiac grand am 2.2 L. It runs really rough on idle in all gears whether it is warm or cold. It pulls out of it when the accelerator is pushed and you don't feel it again until you left off of the pedal. Changed the plugs and harmonic balancer because it was wobbling. There are no codes being pulled and there is no loss of power. I can accelerate pretty fast with no problems. What could cause this?
Pancake wrote:How do you "idle in all gears"? At idle a petrol-powered car is basically operating with a mostly closed throttle plate to minimise fuel used.
ludi wrote:Pancake wrote:How do you "idle in all gears"? At idle a petrol-powered car is basically operating with a mostly closed throttle plate to minimise fuel used.
I assume he means releasing the accelerator while in motion, which then closes the throttle plate, and can expose the effects of a dirty IAC valve, vaccuum leak, or various airflow sensor problems as several posters have indicated.
Pancake wrote:I have a Ford "ute" about the same vintage but had to look up what an IAC valve was as my car doesn't have one. I only really play with my car and thought manually actuated throttles kind of stopped being manufactured in the 90's?!? Isn't everything since then computer controlled throttle servos? Why would you not do that as soon as cars had ECUs?!? Bizarro world!!!
Starfalcon wrote:I would start the car and listen to the engine and see if you can hear a hissing noise...that is always the easy way to track down a leak. Once you have the area it is coming from narrowed down, you can start checking the lines and see which one it is.
Pancake wrote:Why would you not do that as soon as cars had ECUs?!?
synthtel2 wrote:Pancake wrote:Why would you not do that as soon as cars had ECUs?!?
Throttle response.
Glorious wrote:Starfalcon wrote:I would start the car and listen to the engine and see if you can hear a hissing noise...that is always the easy way to track down a leak. Once you have the area it is coming from narrowed down, you can start checking the lines and see which one it is.
You can do the smoke (see where it gets sucked in) or carb cleaner (if the engine races, that's roughly where the leak is) tricks too if you can't actually hear it.
Waco wrote:synthtel2 wrote:Pancake wrote:Why would you not do that as soon as cars had ECUs?!?
Throttle response.
I hear you, but the throttle response on a servo-driven throttle isn't perceptibly worse than cable driven - with the bonus that proper fueling is FAR better since the ECU can set the proper pulse widths and ignition timing as the throttle opens and not in response to the throttle opening.
Short answer: there's no real difference.
synthtel2 wrote:Waco wrote:synthtel2 wrote:Throttle response.
I hear you, but the throttle response on a servo-driven throttle isn't perceptibly worse than cable driven - with the bonus that proper fueling is FAR better since the ECU can set the proper pulse widths and ignition timing as the throttle opens and not in response to the throttle opening.
Short answer: there's no real difference.
I have yet to drive a car with an electronic throttle that truly delivers on that (not that that sampling includes much in the way of high-performance stuff, to be fair). They've got their advantages, but the extra delay / lowered rate of change is perceptible.
The ECU can set fuelling and timings according to changing conditions far faster than a suddenly-opened throttle plate translates into MAP. Trying to set them directly against throttle opening would result in knock when the throttle is snapped shut suddenly, would drop timings too quickly on accel, and would go very rich on early accel before the lean dip accel enrichment is designed to counter (and the inverse on decel). It's far more accurate to use MAP for the heavy lifting and throttle position for tweaks than to try to emulate the intake manifold in software well enough to make throttle position the main load sensor, despite MAP on the face of it not being as responsive.
DragonDaddyBear wrote:Electronic throttles make cruise control much less complicated. Even if the lag is a thing, not many care enough to notice but they would notice no cruise control. Not that it can't be done mechanically but it's far less elegant and not as reliable.
ludi wrote:I've owned or driven at least five vehicles that had the old-school vacuum-driven cruise control connected to a mechanical throttle, and all worked fine (one, a 1998 Camry, still does). What am I missing?
SuperSpy wrote:You haven't truly learned to hate vacuum hoses until you have to diagnose non-functional four wheel drive actuation on an early 2000s Chevy.
The manifold vacuum goes to an electronic switch on the transfer case, which opens a valve, which brings vacuum back up to the engine bay (while crossing dangerously close to the exhaust), to a vacuum cylinder, which pulls on a cable, which pulls a pin that engages the front differential.
Plus, the HVAC diverter system is also vacuum driven, and GM had a lovely issue where the vacuum valve on the transfer case would blow a seal, so the (pressurized) transfer case would force transmission fluid into the HVAC selector, which would ooze out from under the dash.
Captain Ned wrote:Amateurs. Rank amateurs. Behold the vacuum hose routing diagram for a 1985 Civic with the CVCC carburetor.
Captain Ned wrote:Amateurs. Rank amateurs. Behold the vacuum hose routing diagram for a 1985 Civic with the CVCC carburetor.
Chrispy_ wrote:That's the early era of O2 sensors for ECUs, and with electronic fuel injection replacing carburettors and chokes, the idle smoothness is down to either poor injection/ignition (check fuel lines, injectors, sparks and leads) or poor air/fuel mixture (check O2 sensors and ECU error codes).
Glorious wrote:Chrispy_ wrote:That's the early era of O2 sensors for ECUs, and with electronic fuel injection replacing carburettors and chokes, the idle smoothness is down to either poor injection/ignition (check fuel lines, injectors, sparks and leads) or poor air/fuel mixture (check O2 sensors and ECU error codes).
Uhh, not exclusively, it absolutely can be vacuum leaks like many have suggested or the IAC valve like ludi indicated.
IAC valves are typically like ~50 USD, and it's typically two bolts and simple gasket.
Vacuum leaks can be more expensive, depending on how/where, but they can also easily be things like ~10 USD semi-rigid piping/hosing piece, like for EVAP etc... Those can be as simple as picking a part off the shelf (not behind the counter i.e. these pieces fail/degrade all the time!) at the auto parts store and just pop the darn thing on.
Anyway, both of those can absolutely cause a rough idle, and they should absolutely be where you start, not the O2 sensors. (I mean, if the code reader explicitly talks about "O2 high", is the sensor bad, or are you lean cause of the leak? [conversely if you fix what you think was a leak, it might start saying low--not necessarily because it's bad, but because your ECU has been overcompensating etc...])
EDIT: In my experience, the codes give you very rough diagnostic information, but you have to think about the system in totality and try to figure out what that might possibly mean. Unless it's outright obvious already, you very rarely find immediately straightforward answers.