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Tool Hut
Tool Hut, ASE Certified Technician
Category: Chevy
Satisfied Customers: 494
Experience:  Owner of a mobile diagnostics company assisting auto technicians with difficult vehicles
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I have 2000 s10 extreme with 4.3 vortec it is idling rough

Customer Question

Hi I have 2000 s10 extreme with 4.3 vortec it is idling rough throwing the po300 code and it is deisling when I go to turn it off I have replaced plugs wires cap rotor check fuel pressure converted it to the mpi injectors checked the egr valve cleaned and checked pvc valve I am at my limits on it can u help
Submitted: 1 year ago.
Category: Chevy
Expert:  Gary replied 1 year ago.

was everything done to correct this issue ?

NO vacuum leaks at all ?

when its skipping at idle if you remove one plug wire at a time off the cap do any you unplug make NO difference in the idle ?

Customer: replied 1 year ago.
It has good vacum and checked all the plug wires with the timing light it lights up with all of them
Expert:  Gary replied 1 year ago.

ok but at idle will any wires you unplug off the cap NOT make a difference in the idle ?

just be sure there are NO vacuum leaks

Customer: replied 1 year ago.
Just started it and went through them all again they make a slight difference when u pull them
Expert:  Gary replied 1 year ago.

with it setting a 300 code the crank sensor is reading a misfire

usually when all the cylinders will make a difference in the idle when removing spark plug wire and a brand new injection set up these issues come down to a bad crank sensor or the bottom distributor gear worn down enough to change the timing

pull out the distributor and be sure the bottom gear is not worn down at all

any signs of that change the gear or the distributor

if its not worn or was worn and you fixed that and it still does this i would try a new GM crank sensor

Customer: replied 1 year ago.
Is there a way to test the crank postiom sensor
Expert:  Gary replied 1 year ago.

not really due to the signal is puts out to the computer

the power and ground should be good to it since the engine will run but its acting like the timing is off and when that happens its the distributor gear or the crank sensor

Customer: replied 1 year ago.
wouldn't the computer see that the crank postiom sensor was bad and throw the code out for it
Expert:  Tool Hut replied 1 year ago.

Hi, My Name is***** have over 20 years experience repairing vehicles. I am a ASE Certified Master Auto Technician. I am confident we can resolve your problem together.Please remember I don't know your skill level. I can't see, smell, hear, or touch the vehicle. It may take a few back and forth replies to get to a satisfactory resolution.I also try to give all of the information you may need expecting a positive rating. If there is any reason I cannot get a positive rating please let me know.

I have read the back and forth. I think Gary was on the right direction. Have you pulled the distributor and inspected or replaced the drive gear?

Customer: replied 1 year ago.
that was the first thing I did when it started this problem
Customer: replied 1 year ago.
The gear was in good condition no wear to it at all
Expert:  Tool Hut replied 1 year ago.

It didnt have a sharp edge? Sometimes the wear is not obvious. It can look OK and be worn.

Customer: replied 1 year ago.
Nope it did not and rotor and had no excessive movement in the rotation of it either
Customer: replied 1 year ago.
I checked the timing with the timing light and a scan tool and it was reading 10-15 degrees advanced when it was idling what
Expert:  Tool Hut replied 1 year ago.

The scan tool should have had a CMP offset reading. Do you know what that value was?

Have you cleaned the mass air flow sensor?

Do you have a vacuum gauge?

Customer: replied 1 year ago.
I don't not remember what the value was I can run it again and let u know . I removed the mass air flow and looks perfect and no I don't have a vacum gauge put had the brake booster line off and it had good vacum to it all the time
Expert:  Tool Hut replied 1 year ago.

The gauge is the only way to test vacuum. I would clean the mass air flow sensor with brake clean. A piece of fuzz will make it run funny.

Customer: replied 1 year ago.
Do u think it could be crank position sensor
Expert:  Tool Hut replied 1 year ago.

No usually the crank sensor will prevent starting

Customer: replied 1 year ago.
What about the deisling of the motor when go to shut it off that usually means to far advanced but since it is computer controlled what is u take on this part of it
Expert:  Tool Hut replied 1 year ago.

It is only computer controlled from where you set it. That is why I asked about CMP Offset

Customer: replied 1 year ago.
Ok checked vacuum last nite and it was low around 10-12 and it was pulsating what could the problem be
Expert:  Tool Hut replied 1 year ago.

Pulsating is an indication of a broken valve spring or burned valve. Not a good sign.

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