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Idle speed on drive by wire

 
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Knarley Darley
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PostPosted: Thu May 31, 2007 10:39 pm    Post subject: Idle speed on drive by wire Reply with quote

Is there a way to slightly increase the idle on 2000 and newer GM 5.3s, and 6.0s that have drive by wire? Seems like when they get past 80,000 miles and up they idle at 400 rpm and ocasionally stall at idle if loaded suddenly by the AC or power steering. I tried giving the throttle plate and openning a good cleaning, and cleaned the injectors. The car seemed to run better, but the idle is still to low. Any ideas?
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squeeezer
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1991 Chevrolet Camaro

PostPosted: Fri Jun 01, 2007 12:31 am    Post subject: Reply with quote

see if there are and tsb's or campaigns on this issue

a reflash could take care of it Very Happy

i could check for ya tomorrow

need exact year and make etc.
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nwcc
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PostPosted: Fri Jun 01, 2007 12:37 am    Post subject: Reply with quote

Do the drive by wire cars still have a IAC valve to compensate for AC and the like?

Or does the PCM just adjust the throttle motor?
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Paul P
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1971 Chevrolet Chevelle

PostPosted: Fri Jun 01, 2007 6:38 am    Post subject: Reply with quote

Sounds to me like carbon buildup behind the throttle plate. A little carb cleaner on a rag should do the trick. Most tune up shops overlook this detail when diagnosing a stalling condition. There is a certain amount of air that is supposed to get through the throttle plate when fully closed. The AIC can't compensate for no air coming in when there is a carbon ridge just behind it. I've seen this many times on high mileage computer controlled engines.
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Fri Jun 01, 2007 7:14 am    Post subject: Reply with quote

usually a GOOD cleaning is all that is needed. clean the MAF when you have it off. would be a good idea to flush the injectors too if it hasnt been done.
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af2 wrote:
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Knarley Darley
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PostPosted: Fri Jun 01, 2007 10:09 am    Post subject: Reply with quote

Good call everybody. I have already cleaned the heck out of the plate, I open it with one finger, and use carb spray and a small brush and scrub till it shines on both sides, the same thing for the bore arround it, and the injectors. The injector clean gave it noticably more power at part throttle and smooth as can be, but the idle is still below 500 in park which in my opinion is still to low. This is a 02 suburban. Do you think there could be enough build up in the intake trac and on the intake valves to cause this? It has 123,000 on it.
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Knarley Darley
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PostPosted: Fri Jun 01, 2007 10:12 am    Post subject: Reply with quote

Just reread your post. I will try the MAF clean and see what happens.
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Fri Jun 01, 2007 12:03 pm    Post subject: Reply with quote

Knarley Darley wrote:
Do you think there could be enough build up in the intake trac and on the intake valves to cause this? It has 123,000 on it.


it is possible but a good injector flush usually cleans the back side of the valves pretty good because the injectors spray directly on them.

another thing to keep in mind (mostly for those with less experience) DONT TRY TO CLEAN A DRIVE BY WIRE THROTTLEBODY WITH THE KEY ON. the PCM will see the open t-body and close it. bye bye fingers Shocked Crying or Very sad

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af2 wrote:
It seems we can look at our magical Balls and come up with a fix?

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nwcc
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PostPosted: Fri Jun 01, 2007 12:38 pm    Post subject: Reply with quote

10sec.et wrote:
DONT TRY TO CLEAN A DRIVE BY WIRE THROTTLEBODY WITH THE KEY ON. the PCM will see the open t-body and close it. bye bye fingers Shocked Crying or Very sad


Damn!!! Shocked I never would have thought the throttle motor was that strong.
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Fri Jun 01, 2007 12:53 pm    Post subject: Reply with quote

nwcc wrote:
10sec.et wrote:
DONT TRY TO CLEAN A DRIVE BY WIRE THROTTLEBODY WITH THE KEY ON. the PCM will see the open t-body and close it. bye bye fingers Shocked Crying or Very sad


Damn!!! Shocked I never would have thought the throttle motor was that strong.


i got that information from a driveability class. the instructor stuck a Bic pen in one (test vehicle) and it damn near cut it in half.

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SMOKEmUP
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1979 Chevrolet Camaro

PostPosted: Fri Jun 01, 2007 1:44 pm    Post subject: Reply with quote

Do you have access to a scanner? If not the local Autozone here will scan the car for free.

I would look into the O2 sensors. After a while the response time slows down and indicate a false lean condition and the computer over compensates by adding fuel resulting in poor idle. Another thing to look into are the catalytic converter as they may be plugging up. Check for the usual vacuum leaks.

Another thing you might try is to reset the computer. The computer learns the engine's fuel trims and if they are off can cause problems.

To reset:

Turn key on, don't start car
Pull PCM BATT and PCM IGN fuses (should be in engine compartment)
Wait 5-10 min
Turn ignition off
Replace fuses

After it's reset you'll need to drive the car for 30 min to an hour for the computer relearn fuel trims.

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10sec.et
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Joined: 29 Mar 2006
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Location: Houston,Texas
346658.74 points


1969 Oldsmobile Cutlass

PostPosted: Fri Jun 01, 2007 4:30 pm    Post subject: Reply with quote

SMOKEmUP wrote:

Another thing you might try is to reset the computer. The computer learns the engine's fuel trims and if they are off can cause problems.

To reset:

Turn key on, don't start car
Pull PCM BATT and PCM IGN fuses (should be in engine compartment)
Wait 5-10 min
Turn ignition off
Replace fuses

After it's reset you'll need to drive the car for 30 min to an hour for the computer relearn fuel trims.


before driving the truck give it a few minutes idling in park with all accys off then with ac turned on. that will give it time to "learn" idle. also a problem with intake leaks on those motors but you need to look at fuel trim to find it. the PCM is too quick to try the old "spray carb cleaner and listen for rpm change". you wont notice any difference without monitoring the data.

these trucks are also sensitive to low voltage. if you have a bad battery or bad cable connections it will cause weird problems.

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It seems we can look at our magical Balls and come up with a fix?

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