very low idle
Thread Starter
Instructor
Joined: Nov 2007
Posts: 101
Likes: 6
From: gozée belgium
very low idle
hello
when i leave home, after one or two kilometers, I stop in an intersection,my idle drops at 500 rpm and rises back to 750 when I really stop;
it's very low and I feel like she will stall but she does not .
I feel it is getting worse
what it could be ?
thanks for your help
excuse my poor english
when i leave home, after one or two kilometers, I stop in an intersection,my idle drops at 500 rpm and rises back to 750 when I really stop;
it's very low and I feel like she will stall but she does not .
I feel it is getting worse
what it could be ?
thanks for your help
excuse my poor english
Racer
Joined: Feb 2013
Posts: 350
Likes: 0
From: Saratoga NY
Nope not at all. I just drove it and I do have to say it was more like 600 rpms not 500. But it runs great
Is your mpg gone down a lot lately? How clean is your air filter? What have u checked and when was your last tune up
Is your mpg gone down a lot lately? How clean is your air filter? What have u checked and when was your last tune up
CF "Young" Senior Member
Joined: Feb 2005
Posts: 4,034
Likes: 26
From: Cupertino CA
St. Jude Donor '12
Something else to look into is the throttle body. At ~60-70k I had to have mine cleaned, just some throttle body cleaner spray picked up at the local parts store. It made the difference between an A4 stalling just sitting at a stop and running smoothly.
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Melting Slicks
Joined: Sep 2011
Posts: 2,258
Likes: 544
From: Appleton WI
Does your car have an automatic or manual transmission? If manual, does the RPM raise to 750 after you push the clutch in and come to a complete stop? You may be slowing down in a gear that is too high for the speed and you're lugging the engine below the normal idle RPM. This is more noticeable when the engine and transmission are cold. Now that you are watching for this condition, you might be noticing it more even though it was happening all along. You wouldn't be the first person to do this. If this is the case, you can either choose a different gear, push the clutch in sooner, or ignore it.
If I did my conversion correctly, your fuel use looks ok. I'm estimating you're getting ~19.8 MPG. I'm assuming you do quite a bit of in town stop and go driving. Have you noticed a change in fuel use?
If I did my conversion correctly, your fuel use looks ok. I'm estimating you're getting ~19.8 MPG. I'm assuming you do quite a bit of in town stop and go driving. Have you noticed a change in fuel use?
Thread Starter
Instructor
Joined: Nov 2007
Posts: 101
Likes: 6
From: gozée belgium
It s a 6 speed.
She has 112500 miles and i own her for 5 1/2 years.
When i slow down i press on the clutch pedal
and when i m almost stop the idle drops at 500 and
even below.
I think it s not normal cause she did not do
this before. The idle never dropped below 750.
This appears a few weeks ago.
She has 112500 miles and i own her for 5 1/2 years.
When i slow down i press on the clutch pedal
and when i m almost stop the idle drops at 500 and
even below.
I think it s not normal cause she did not do
this before. The idle never dropped below 750.
This appears a few weeks ago.
Melting Slicks
Joined: Jul 2013
Posts: 2,012
Likes: 23
From: Anaheim CA
I'm seeing 500 consistently on my A4...just assumed that was normal for this size/type engine.
One odd thing is that I've looked everywhere obvious in the service manual(s) and cannot find any specification for idle speed. Seriously?
One odd thing is that I've looked everywhere obvious in the service manual(s) and cannot find any specification for idle speed. Seriously?
Race Director
Joined: Jan 2007
Posts: 18,643
Likes: 14
From: Norman Oklahoma - The Only State in the Union with no Blue Counties!
Idle RPM is controlled by the ECBM computer. "Normal" for any LS engine is 750 RPM after the engine is warmed up. The engine should run around 100 RPM higher until it is warmed up. When you turn on the AC compressor the computer bumps your idle up about 50 RPM to compensate for the increase in load.
OP, since your car is not running in this manner and no changes in the computer program has been made then you must have a mechanical reason for the change in behavior.
Air filter, dirty fuel injectors or a bad one, dirty mass air flow sensor, bad spark plug or spark plug wire or a combination of all of these might be the culprit.....even bad gasoline
I am no mechanic but I would eliminate the possible causes and go from there.
p.s. Your english is WAY better than my Swedish!
OP, since your car is not running in this manner and no changes in the computer program has been made then you must have a mechanical reason for the change in behavior.
Air filter, dirty fuel injectors or a bad one, dirty mass air flow sensor, bad spark plug or spark plug wire or a combination of all of these might be the culprit.....even bad gasoline
I am no mechanic but I would eliminate the possible causes and go from there.
p.s. Your english is WAY better than my Swedish!
Racer
Joined: Mar 2012
Posts: 446
Likes: 1
From: Christiansburg VA
I've got another cause: faulty Intake Air Temp sensor or wiring. My C5 had the same behavior, and starting throwing IAT codes after a while. The cause was a broken wire going to the IAT. Hard to find, as the insulation was still intact. If you can get your hands on a scan gauge, that makes diagnosing the problem a LOT easier.
Melting Slicks
Joined: Nov 2008
Posts: 3,146
Likes: 203
From: Edmonton Alberta, Canada
I had same issue low idle and it was the air filter. I replaced it and after about two days it now idles at 750-800 rpm. It took a couple of drives before the idle recovered. Also some sea foam fuel additive is a good idea. Good luck, Rob
Thread Starter
Instructor
Joined: Nov 2007
Posts: 101
Likes: 6
From: gozée belgium
good news 
Yesterday I cleaned the throttle body who was a bit dirty, and also cleaned the MAF and air filter.
this morning on my way to work, my vette has run perfectly. cold idle at 1000 rpm and after heating at 750-800 rpm
thank you all
I speak french
Yesterday I cleaned the throttle body who was a bit dirty, and also cleaned the MAF and air filter.
this morning on my way to work, my vette has run perfectly. cold idle at 1000 rpm and after heating at 750-800 rpm
thank you all
I speak french
Melting Slicks
Joined: Jul 2013
Posts: 2,012
Likes: 23
From: Anaheim CA
As I said, I can't find anything in the service manual, even under the section for diagnosing "bad idle".
Advanced
Joined: May 2008
Posts: 87
Likes: 0
From: Chicago IL
I just cleaned the throttle body last night. Wasn't too dirty but since I haven't done since I bought the car 5yrs ago thought it was time to clean it.
After cleaning it and driving this morning I noticed the rpm's were a bit high, around 700-750 in park and on D around 500-550. Also noticed that when slowing down at about 600 it does a quick jump to 700-750, which It never did before. Engine is basic stock just for the Vararam and XS Power headers and X pipe and mail in tune. (automatic trans)
Can anyone tell me if this is normal after a TB clean? What can I do to stop that quick rpm jump?
Appreciate any input.
After cleaning it and driving this morning I noticed the rpm's were a bit high, around 700-750 in park and on D around 500-550. Also noticed that when slowing down at about 600 it does a quick jump to 700-750, which It never did before. Engine is basic stock just for the Vararam and XS Power headers and X pipe and mail in tune. (automatic trans)
Can anyone tell me if this is normal after a TB clean? What can I do to stop that quick rpm jump?
Appreciate any input.
Melting Slicks
Joined: Nov 2008
Posts: 3,146
Likes: 203
From: Edmonton Alberta, Canada
All the rpm numbers are normal operation but the jump is questionable. Is the air conditioning on or off? Try turning it off if it is on and see if there is any difference. I think it is a rpm bump to maintain AC pump drag. Good luck, Rob