Google Groups no longer supports new Usenet posts or subscriptions. Historical content remains viewable.
Dismiss

2002 C5 Rough Idle?

273 views
Skip to first unread message

Crow

unread,
Aug 30, 2002, 7:38:38 PM8/30/02
to
My 2002 C5 has developed a rough idle and hesitation while shifting
(automatic) after 2,000 miles. Had it to the dealer today and it was
diagnosed as no problem found i.e., no computer codes. I can feel it
miss intermitantly and can see it in the engine while idling. I have
also noticed that my normal weekly driving which usually yeilds around
26 MPG is now at about 24 MPG - not a huge difference but noticable.

I'm using regular unleaded (87 octane) from the same gas station I've
always gone to and now I'm wondering should I use 91?

Any ideas would be appreciated.

tos...@aol.com ab...@aol.com ab...@yahoo.com ab...@hotmail.com ab...@msn.com ab...@sprint.com
ab...@earthlink.com u...@ftc.gov ab...@fbi.gov ab...@cia.gov ab...@nsa.gov

James Alrad

unread,
Aug 30, 2002, 8:03:55 PM8/30/02
to
On Fri, 30 Aug 2002 23:38:38 GMT, thec...@charter.net (Crow) wrote:

>My 2002 C5 has developed a rough idle and hesitation while shifting
>(automatic) after 2,000 miles. Had it to the dealer today and it was
>diagnosed as no problem found i.e., no computer codes. I can feel it
>miss intermitantly and can see it in the engine while idling. I have
>also noticed that my normal weekly driving which usually yeilds around
>26 MPG is now at about 24 MPG - not a huge difference but noticable.
>
>I'm using regular unleaded (87 octane) from the same gas station I've
>always gone to and now I'm wondering should I use 91?
>
>Any ideas would be appreciated.


Why in the world would you use 87 octane in a C5 when the minimum
requirement is 91?


Tom Scales

unread,
Aug 30, 2002, 8:47:04 PM8/30/02
to
Uh, yes

Your car requires premium.

Also, try various brands until you find the one it likes best. It will
particularly like a 93 octane.

Tom
"Crow" <thec...@charter.net> wrote in message
news:3d6ffc51...@news.charter.net...

Crow

unread,
Aug 31, 2002, 1:13:02 AM8/31/02
to
Good question. I guess because my owners manual says 87 octane is
fine. I'll try premium - at least 91 octane.

Kent

On Sat, 31 Aug 2002 00:03:55 GMT, James Alrad <nos...@hotmail.com>
wrote:

tos...@aol.com ab...@aol.com ab...@yahoo.com ab...@hotmail.com ab...@msn.com ab...@sprint.com

The Monk

unread,
Aug 31, 2002, 10:35:09 PM8/31/02
to
On Sat, 31 Aug 2002 05:13:02 GMT, thec...@charter.net (Crow) wrote:
>Good question. I guess because my owners manual says 87 octane is
>fine. I'll try premium - at least 91 octane.

Save that owner's manual! It could be a valuable collector's item!!!

Seriously, the official spec calls for "Premium Unleaded Fuel". I use
Sunoco Ultra 94... cause here where I am it's actually cheaper than
Mobil Premium. Go figure! Anyway... the car absolutely loves it!!!

Monk
1998 C5 Coupe

Crow

unread,
Sep 14, 2002, 2:13:16 PM9/14/02
to
My previous post had to do with my C5 idling roughly while running 87
octane gas (my bad). I ran a total of 5 tank fulls through it and
have since changed to Chevron 91 with Techrolene (sp?). I've run 2
tanks of this and I still have a rough idle.

I'm now considering using an injector cleaner. What's the best I can
use or should I use any at all?

Thanks, Kent

Baboo

unread,
Sep 14, 2002, 6:04:52 PM9/14/02
to
OMG, I hope you do not have to take her to the dealer. They can not afford
malpractice insurance.

be sure to understand http://www.anti-matrix.net

Buhda

unread,
Sep 15, 2002, 8:49:50 AM9/15/02
to
try running 93..which is PREMIUM gas....

"Crow" <thec...@charter.net> wrote in message

news:3d837bc6...@news.charter.net...

Crow

unread,
Sep 15, 2002, 5:39:05 PM9/15/02
to
I can't find any 93 in my area.

On Sun, 15 Sep 2002 12:49:50 GMT, "Buhda" <taras...@hotmail.com>
wrote:

Buhda

unread,
Sep 16, 2002, 4:19:49 PM9/16/02
to
Try octane boost?

"Crow" <thec...@charter.net> wrote in message

news:3d84fde...@news.charter.net...

James Alrad

unread,
Sep 16, 2002, 4:47:34 PM9/16/02
to
On Sun, 15 Sep 2002 12:49:50 GMT, "Buhda" <taras...@hotmail.com>
wrote:

>try running 93..which is PREMIUM gas....
>


That won't affect the idle.

The cleaning additive in Chevron is Techron which is supposed to be
one of the best. Try buying some Techron additive at the station store
and follow instructions. That will give a more concentrated cleaner.


Corey872

unread,
Sep 17, 2002, 11:07:09 AM9/17/02
to
First, the injectors on an 02 can't be THAT dirty...well, maybe if you
ran a shovel full of mud in the tank, but many cars run 150,000+ miles
on 87 octane with no injector cleaner. More likely your computer came
up with some conservative fuel and timing settings to deal with the
low octane. I would first disconnect the battery (-)for 30 seconds or
so, which should re-set all long term fuel maps for the computer and
see if that helps. The car may again run bad at the start, but should
get better at the computer "learns" on the 92 octane.

Corey
thec...@charter.net (Crow) wrote in message news:<3d837bc6...@news.charter.net>...

Crow

unread,
Sep 21, 2002, 5:57:12 PM9/21/02
to
Finally figured it out. I'm very disappointed the dealer couldn't. I
had to perform the Idle Learn Procedure. Idles and shifts as smooth
as silk.

If anyone is interested, I can post the details.

Kent

On Fri, 30 Aug 2002 23:38:38 GMT, thec...@charter.net (Crow) wrote:

Frank Errico

unread,
Sep 22, 2002, 7:03:46 PM9/22/02
to
I have had autos that just won't idle with Chevron gas. I won't even think
aboout putting that stuff in my Z06.

"Crow" <thec...@charter.net> wrote in message
news:3d837bc6...@news.charter.net...

Dave

unread,
Sep 23, 2002, 12:21:05 AM9/23/02
to
I'm interested. What's the 'Idle Learn Procedure'?
Dave

Crow

unread,
Sep 23, 2002, 2:54:02 AM9/23/02
to
Idle Learn Procedure

Anytime the powertrain control module (PCM) or the battery
is disconnected, the PCM loses power, or the PCM is
reprogrammed, the PCMs learned idle position is lost. The
engine idle is unstable (rough idle, hesitant shifting) when the
learned idle position is lost. This can also occur even though the
correct number of steps are displayed by the computer because it is a
stepper motor without any feedback; the motor can lose its place.

Perform the following procedure in order to return the learned
idle to the correct position:

Automatic Transmission

1. Ensure the engine coolant temperature is more than 80°C
(176°F)
2. Turn OFF the ignition.
3. Remove PCM fuses (16&23) under hood and wait 10 minutes.
4. Reinstall the PCM fuses (16&23).
5. Set the parking brake and block the drive wheels.
6. Start the engine. Turn OFF the A/C controls. Ensure the engine
coolant temperature is more than 80°C (176°F).
7. Shift the transmission into Drive.
8. Allow the engine to idle for 5 minutes.
9. Shift the transmission into Park.
10. Allow the engine to idle for 5 minutes.
11. Turn OFF the engine for 30 seconds.

Manual Transmission

Same as above except:
7. Place the transmission in Neutral.
8. Start the engine. Ensure the engine coolant temperature is more
than 80°C (176°F).
9. Allow the engine to idle for 5 minutes.
10. Turn OFF the engine for 30 seconds.

0 new messages