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Ron Z.
Ron Z., - Cadillac Tech -
Category: Cadillac
Satisfied Customers: 17948
Experience:  18+yrs experience. State Inspector and Cadillac Diagnostics
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I have a 2003 cts idles rough .. up and down service engine

Customer Question

I have a 2003 cts idles rough .. up and down service engine light is on .. have been dealing with this for some time now .
I started it a couple weeks ago and rps shot up to 3k -4k so i disconnected battery let sot for couple days now it is just rough but still not right. Can u help me out ?
Submitted: 1 year ago.
Category: Cadillac
Expert:  Ron Z. replied 1 year ago.

I'm sorry the Tech you requested was unavailable to assist you today. It appears that Tech is currently "Offline". Now that his 15 minute "request lock" has expired, hopefully I can be of some assistance in his place...

Can I have all the p-codes that were retrieved from the AutoZone scan?

Customer: replied 1 year ago.
Im in route to get it scanned it says "service idle control" on my screen on dash
Expert:  Ron Z. replied 1 year ago.

Ok. Get those codes, let's see what we can figure out here.

Customer: replied 1 year ago.
P0121..p1795.. p2176..p0507..p0221..p1780..p1780Most are throttle positon sensor .. alsa says something about reprogramming the car to new throttle position .. the one on my car looks fairly new its a bosch .. the sensor that hooks to intake and throttle body
Customer: replied 1 year ago.
Im trying to send a pic but it wont let me
Expert:  Ron Z. replied 1 year ago.

OK. Looks like TP codes, Idle Control codes and a couple transmission codes. THe TP plays a role in the transmission operation, so I believe the transmission codes are just by-products of the symptoms being created by the other codes. On this vehicle, the TP Sensor is built into and part of the Throttle Body assembly and is usually not recommended to be replaced as a stand-alone item. So if it looks like it's new, and it was replaced with an aftermarket part.... this very well could be the root of the problem. My advice at this point would be to carefully inspect the electrical connector and wire harness for any loose, broken or damaged wires. If the visual inspection checks ok, I'd say run a quick cleaning of the throttle body. Use a toothbrush and some carb cleaner and try to get as much build up out as you can. Get the bore, plate and plate pivot points. If the cleaning does not resolve the problem or helps temporarily, then I believe the Throttle Body Assembly is going to need to be replaced. Please do the right thing and remember to leave a rating using the rating system at the top of this page or accept the answer so I may be credited for this Q&A. You can ask follow-up questions any time, even after you rate or accept.

Customer: replied 1 year ago.
What about reprogramming the comp. Or will i have to do anything regauding computer if i replace it ?
Expert:  Ron Z. replied 1 year ago.

After throttle body replacement, there is an "Idle Relearn Procedure"

Perform the following procedure in order to allow the ECM to learn the idle position:

  1. Ensure that the following conditions are met:
    • The vehicle speed is 0 mph.
    • The accelerator pedal angle is less than 14.9 percent.
    • The battery voltage is more than 10 volts.
    • The engine coolant temperature (ECT) is between 5-60°C (41-140°F).
    • The intake air temperature (IAT) is more than 5-60°C (41-140°F).
  1. Turn OFF the ignition for 30 seconds.
  2. Turn ON the ignition, with the engine OFF for 1 minute.
  3. Turn OFF the ignition.
  4. Clear DTCs as necessary.

You can even give this a run-through now if you believe the TPS was replaced but not relearned. But, like I say, the TPS usually ins't a stand-alone serviceable item, so even if it was replaced, that is probably part of the problem.

Please do the right thing and remember to leave a rating using the rating system at the top of this page or accept the answer so I may be credited for this Q&A. You can ask follow-up questions any time, even after you rate or accept.

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