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Category: Chevy
Satisfied Customers: 26645
Experience:  ASE certified tech ADVANCED LEVEL SPECIALIST. Wisconsin certified emissions state inspector
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Chevrolet Suburban K2500 4x4: 2003 suburban 6.0 rough idle.

Resolved Question:

2003 suburban 6.0 rough idle. Replaced the APP, Throttle body (2x) and the wire harness for the TB, and put in a brand new battery. 800 bucks in parts and still bad idle. Oh yeah, also the front O2 sensors. help
Submitted: 5 years ago.
Category: Chevy
Expert:  AMEDEE replied 5 years ago.
Hello and Welcome to Just Answer. My name is XXXXX XXXXX I will try my best to assist you and your 100% satisfaction is my goal. I have been working on these vehicles for over 10 years so I am very familiar with this system and how they work. However, keep in mind, that I need some solid concrete facts/evidence/clues from you in order to give you a good answer about your vehicle. Please realize that all my answers are based solely on the info that you provide me with.

Is the check engine light on?

Are there any codes in the computer?

Does the engine ever stall out on you?
Customer: replied 5 years ago.

No check engine, there are no codes my scanner can pick up although I am going to try to get to my garage guy this weekend and get him to read it with his scanner.


It has not stalled out, today it started idling about 1000rpm and it seems like when I get to 2k rpm it just wants to hesitate.


I replaced all the other parts because I was getting codes and engine light on. The codes indicated that the TB controller was having issues. I was having the truck go into "limp" mode fairly often. Since replacing all those parts it has not done that at all, now just the idle issue.

Expert:  AMEDEE replied 5 years ago.

Was the throttle body itself replaced?
Customer: replied 5 years ago.
yes, twice. After the 2nd one we checked the codes again and they were the same, I forget the exact number but they indicated a voltage difference between the 2 sides of the APP and the throttle body. That is why I replaced the APP and the battery (we were reading some forums that indicated that a weak battery might cause of the symptoms I was seeing).
Expert:  AMEDEE replied 5 years ago.

You might have an air or a vacuum leak. This is very common! Open the hood and listen for a hissing sound when the engine is running. Unmetered air can enter the engine through a vacuum leak, a dirty airflow sensor that is not reading airflow accurately, an EGR valve is not closing and is leaking exhaust into the intake manifold, an EGR valve that is allowing too much flow.

Possible Causes
Check for air leaks in the Air Induction system (e.g., in the intake manifold)
Check for air leaks in the PCV system and in its related hoses and/or valve
Idle air inlet passage or throttle bore is dirty or full of deposits
MAF sensor is dirty, "skewed" or installed improperly
Throttle plate, throttle shaft or linkage is damaged or sticking
TP sensor is out-of-range or "skewed" high
Customer: replied 5 years ago.

I can check and work on that tomorrow night / Saturday. Where is the idle air inlet passage? I took the air cleaner and the MAF sensor open and cleaned them out also.


Can I reach you through this site when I check those things?

Expert:  AMEDEE replied 5 years ago.
This engine has throttle by wire meaning there is no idle air control motor.

YES.. just reply back to me on this page after checking these things.
Customer: replied 5 years ago.

Ok, I could not find any vaccum leaks and then this morning I got the "Reduced engine power" right after I started it. Turned it off and got my code reader. It threw a P1125 - APP sensor code.


This thing is starting to get very dependable on doing its stuff. I start it up, it will idle rough and then when I start moving I get to about 2K RPM and it starts "surging". As soon as I get to about 2200 it smoothes out. The whole time I am driving though because I am never much over 2500 rpm it always seems like it is on the verge of going into Reduced Power mode...just seems like it is hesitating a little all the time. Any more ideas?

Expert:  AMEDEE replied 5 years ago.
IF you just got the APP sensor code and this sensor has been replaced already, you are going to want to check the inputs to this sensor and the wiring to and from this sensor. Besides a bad PCM, that would be the only other logical reason for this code.
Customer: replied 5 years ago.

Inputs into this sensor? Is that what comes from the position of the gas pedal? Is there a procedure for testing the wiring harness? I have been reading a lot lately about the wiring harness itself having issues...

What is the possibility that the ground on the back passenger side of the block, even though it is tight, is corroded or something and not making good contact?



Expert:  AMEDEE replied 5 years ago.
YES! This does happen from time to time! Check grounds at the rear of the engine, G103, G104. Also, check the Accelerator Pedal sensor connector itself for water or corrosion.
Customer: replied 5 years ago.
Ok, last question for tonight. HOW DO YOU GET TO THAT STUPID G103 :) I got my fingers on it, but no way to get a wrench on it. Also, where is G104 - I have heard of that one but could not find it. Diagrams would be helpful...
Expert:  AMEDEE replied 5 years ago.
Unfortunately, I cannot send any diagrams as it is against copy write laws to do. However, They are not easy to get to. You may have to get to them from the wheel well or from underneath. Ground 103 is on the passenger side head or intake bolt near the rear of the engine. Ground 104 is located on he drivers of the engine also on the rear of the engine either on the cylinder head or the intake.
AMEDEE and 2 other Chevy Specialists are ready to help you
Customer: replied 5 years ago.

Redid both grounds, still the same issue. At this point I am trying to find a APP sensor from a junked Suburban or Tahoe to replace the aftermarket one I put on. This whole process has been a pain in the butt...


I'll let you know how I make out.



Expert:  AMEDEE replied 5 years ago.
Sounds good!

Thanks for the update!