Absolute throttle position

[Jan Rehak]

Hello, I´m from Czech republic, so i am sorry for my english.

I bought Tahoe 2000 5.3 with rough idle, it seems like light misfires. So I changed spark plugs, wires, all 4 O2 sensors, cleaned throttle body and maf sensor, water temp sensor, fuel regulator, PCV valve, checked fuel pressure (57psi), checked vacuum leak with smoke test and spray, new air and fuel filter. But still no change, and no error codes…

No any smoke from exhaust. Short term fuel jump between -2% / +2%.

Idle at warm engine is around 570, but diagnostic show "ABSOLUTE THROTTLE POSITION - 0,0%", is it good or not?

Thank you for yours answers and opinions, Jan R.

 

[Kraig]

Throttle at idle should be 0–does it rise when you apply throttle?
No check engine light/codes? Might try running some injector cleaner through it.

 

[Jan Rehak]

Throttle at idle should be 0–does it rise when you apply throttle?
No check engine light/codes? Might try running some injector cleaner through it.

Yes it moves from 0% to 100% (full throttle).
no CHECK ENGINE LIGHT, no CODE

 

[HiHoeSilver]

Hard to narrow down without a specific misfire code, but maybe coil packs?

 

[Jan Rehak]

Hard to narrow down without a specific misfire code, but maybe coil packs?

The coils were tested and all should be ok. Is a possibility how to test injectors?

 

[Jan Rehak]

I tested compression today :

#8 160psi. #7 169psi
#6 156psi. #5 160psi
#4 162psi. #3 148psi
#2 168psi. #1 148psi

Is 148psi too low, or is it still ok? Thank you

 

[retiredsparky]

a little carbon on intake valves could cause the lower compression. The slight missing could also be caused by injectors not properly atomizing. You could watch internet videos on how to clean them with fuel injection cleaner. Youtube has multiple videos on an inexpensive method of doing this. It involves using the cleaner to pressurize the injector and then powering the injector to operate the solenoid. It will be obvious if an injector has an uneven spray pattern. Or you can take the injectors to a shop to have them tested/cleaned.

 

[Jan Rehak]

Thank you for your response. I sent yesterday injectors for cleaning. If you disconnect the MAF while the engine is idling, do you see any change? nothing happens on my car.

 

[Kraig]

It runs off default data with the MAF disconnected—not ideal and it will trigger a fault code, but it should run without MAF input.

 

[Jan Rehak]

Thank you, now I'll waiting for a clean injectors.