Truck idle high after throttle cleaning code P0121

Pat

Silverado 2500 HD Stalls

Unread post by Pat » Fri Feb 19, 2010 1:29 pm

2003 Chevy Silverado 2500 HD
6.0
Check engine light.
GM computer Codes- No.
Work done to repair this problem = No repairs dealer mech checkef for problems and found none said it was a connection problem in wiring.
GM tech:
question = The engine goes to limp mode for no reasion. No warning. Does not do it when truck is under load (pulling trailer ect.) May not do it and may do it six times in the next forty miles.

JK

Re: Silverado 2500 HD Stalls

Unread post by JK » Fri Feb 19, 2010 1:31 pm

If the check engine light come on, then there must be codes stored in the computer.
These codes may be the key to the stalling.
Any number of sensor could cause this.
Also, may be loosing fuel Pressure. Need to have that checked as well.
If they found a poor connection, it may not have been completely repaired, or there may be another in the same general area of the last repair.

Roy

Truck idle high after throttle cleaning code P0121

Unread post by Roy » Wed Apr 03, 2013 7:52 am

After cleaning carbon from the throttle body of my 2008 Chevy Silverado it seems to idle up and down, but it stays idling high after i give it a little gas then come to a stop. Could this be a sensor in the throttle body or a vacuum leak. We cleaned the throttle because of and engine light code P0121 on the scanner.

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ProTech
Posts: 651
Joined: Wed Oct 17, 2012 10:08 am

Re: Truck idle high after throttle cleaning code P0121

Unread post by ProTech » Thu Apr 04, 2013 6:48 pm

This sometimes happens after a throttle bore cleaning due to the idle position that the computer has learned is now not correct. As the throttle builds up carbon deposits, the computer will re-calculate the idle position so it can get the appropriate amount of air to the engine. After a good cleaning, the old idle position is basically letting in too much air, hence the high idle.

What needs to be done is an idle learn reset, but this will require a scan tool. Sometimes driving it for a while, even up to a few hours, the idle will eventually relearn on it's own.

A few instances, which I've seen myself, the computer can't seem to compensate properly and needs to be reprogrammed to correct the issue. This again would require a scan tool and your local GM dealership.

Take it for a long drive, some highway and some stop and go driving. If this doesn't help, you'll need to either get the idle reset, or the computer reprogrammed.
GM Dealer Technician For 18+ Years
In the automotive industry for 20+

ledodgen
Posts: 1
Joined: Mon Sep 16, 2013 2:49 pm

Truck in Limp Mode

Unread post by ledodgen » Mon Sep 16, 2013 2:54 pm

2004 Chevy Silverado stuck in Limp Mode. I have replaced 1/2 and 2/3 relays and still have problem. What should I check now? Had codes of P0300 and P0753.

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carriedi
Posts: 2573
Joined: Wed Apr 10, 2013 12:42 pm

Re: Truck in Limp Mode

Unread post by carriedi » Mon Sep 16, 2013 11:23 pm

not sure what is going on here. why did you replace the relays? Do you have tranny codes? before you change anything did you check if the trans computer was sending out a signal to those relays?

Trans goes into limp mode if there are codes stored somewhere in the system. What codes have you found?
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