AC makes it idle rougher.
Car idle is rough Inspection Service & Cost
A rough idling engine can be caused by a number of issues, some of them are serious while others tend to be minor, but the symptoms remain pretty much the same. The car will feel rough and bouncy when the engine is running. The car will also idle below its regular speed, display inconsistent RPMs and may produce a shaking, skipping or slipping sound when the vehicle is running.
While a rough idling engine may seem to be a simple inconvenience it often indicates a deeper problem within the engine. The vehicle should be inspected and repaired as soon as possible because small problems have a way of turning into expensive repairs.
How this system works:
The idle speed of an engine is basically the rotational speed the engine runs on when it is un-coupled from the drivetrain and the throttle pedal is not being depressed. The idle speed is measured in the revolutions per minute of the crankshaft.
When an engine is running at idle speed it generates enough power to smoothly operate equipment such as the water pump, alternator, and power steering but not enough power to move the vehicle itself. A passenger car will usually idle between 600 RPMs and 1000 RPMs. A properly functioning idle should run smoothly without skipping or slipping.
Common reasons for this to happen:
SOURCE: 2001 v6 escape rough idle when cold
To update my earlier repair on the 2001 6 cyl Escape: When cold, and when the ignition was turned over but no accelerator pressure given, the rough idle finally returned the P0303 code again when the check engine light came on indicating that it wasn't caused by the plugs or the coil. FYI, I had replaced the intake manifold gaskets during the original repair and just prior to that I had replaced the fuel filter which was very dirty (I cut it open to see).
The repair manual referred to fuel injectors as a possible problem. I have run three tanks of fuel using different injector cleaning products and am very pleased with the results. Cold starts are much smoother and I am unable to coax out the P0303 code or any other code.
My opinion, change the fuel filter, use a fuel injector cleaner for a couple of tanks, change the plugs if the problem still exists. The coils were not the problem on my vehicle.
SOURCE: 2001 Forester, Rough idle and engine loping driving at low rpm
I had a similar problem on my 2002 Impreza RS 2.5 (same engine and engine control system). In my case it was the O2 sensor on the intake manifold. This happened at 34,xxx mi. so it was covered by the warranty. Replacing the part is very easy. (two bolts and a wiring harness). Obviously I would start simple and cheap and work your way to expensive and difficult.
From my understanding its all caused from the engine missfiring. If its been a while or never, I'd change the spark plugs first. (stick with the Subaru Parts plugs, I went after market and the dealer claimed the plugs were not the correct "temperature" and had to pay for the new plugs and install although they did it without my permition. Thats a whole nother story).
Could also be the manifold pressure sensor.
Either 02 or manifold pressure sensor may cause intermitent check engine light.
Where I live Brookline,MA , Autozone will run a free diagnostic on your car by hooking up to your ECU and will give you the trouble codes and possible remidies. Of course there are no guarentee's but it will point you in the right direction.
Good Luck
SOURCE: my1999 madza 626 idles rough when its in drive or when i cut on
this could be a case of carbon debris in the throttle body plates and idle air control chambers...simply might just need serviced/cleaned...pull air intake off throttle body and spray with a good throttle body cleaner spray including the idle air ports. Ive also seen motor mounts cause this as this is more of a vibration felt in gear
SOURCE: my 92 honda accord ex as a rough idle at stop and
Typically this a result of bad motor mounts, I had the same issue with my 92 honda accord, changing the side mounts and the strut up front resolved the issue. The Trans mount, behind the motor is the most difficult mount to change and requires you to unbolt the other mounts and roll the motor far enough forward to gain access to that mount, but once all 4 mounts are replaced your issue should be resolved
SOURCE: 2000 ford expedition ,,rough idle in park..rough
Check the fuel pressure at the rail assembly, there should be a min of 40 lbs at the rails. Do you have any loss of power under a load? You may have an issue with your o2 sensor that is causing the ecm to send an improper signal to the engine ign/fuel map.
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