1993 Near Mint Sunbird V6 3.1L Erratic Idle / Running Rough

rstivers1989

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Alright folks, I need some real help with this one, it is a dousey.

I have an erratic idle with my 1993 near mint Pontiac Sunbird 3.1L V6.

Sometimes: Start car up, goes to 2000 RPMs then settles instantly to regular idle (700ish w/out AC, 1000-1100 w/AC On).

Sometimes: Start car up cold, goes to 2000 RPMs and stays at 2000, or waffles between 1000 RPMs and 2000 RPMs, sounds really rough, eventually Code 35 (IAC Issues) pops. Engine is clearly missing during this 1000 - 2000 RPM issue.

Sometimes: The issue will happen if the car is warm (200+) but not 220 degree, again, Code 35, 1000-2000 RPMs.

ALWAYS: When engine is at 220 degrees, shut off, and then restarted the issue ALWAYS happens. again, Code 35, 1000-2000 RPMs.

Note: Data below is reflected in ALL circumstances (normal operation + during erratic idle) - I do not know if these are relevant, but they seemed interesting to my uneducated mind.

-Exhaust 02 Stays Rich for 30 seconds, then goes Lean/Rich back and forth constantly
-Battery starts out at 10.5 volts and drops as low as 8.5


Things I have already done:
Replaced IAC
Replaced Throttle Body Gasket
Replaced Battery
Replaced Throttle Position Sensor
Replaced O2S Sensor
Replaced Radiator and Heater Core (this solved a pre-existing "running hot" issue)
Replaced Thermostat
Replaced PCV Valve
Replaced TCC Solenoid
Replaced all Coolant Hoses
Replaced Water Crossover Coolant By-Pass Tube
Fuel System Cleaning with Intake Manifold Cleaning using Motor Vac Fuel Injection Cleaning System
Cleaned Throttle Body
Cleaned IAC
Cleaned pretty much every terminal I can find
Checked for Vacuum Leaks

Prior work on the car done recently (likely unrelated to the issue, but noting just for posterity):
Air Conditioning Compressor Replaced
Serpentine Belt and Tensioner Replace
Rear Breaks (Full) Replacement (Calipers, Rotors, etc)
ABS Front Right Wheel Sensor Replaced
Spark Plugs and Wires

My current thought is that it might be an issue with the ECM or the Fuel Injectors, but with the Fuel System having been cleaned so recently, I was leaning towards ruling out the Fuel System.

Note: I have an acutron OBDI reader that can give me live diagnostic data, I can provide data on specific points if it will be helpful.

Would be grateful for any assistance you can offer, sadly there are limited mechanics in my area willing to tackle these problems.
 

melsg5

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Are you saying your car battery reading is 10.5 volts and drops to 8.5 volts?
These readings are with a multimeter?
 
G

G-435385

I had idle issues with my 91 with the 3.1L....found that the speed sensor connection was full of water....cleaned it up and VROOM back to normal. Speedometer was whacking out also. Maybe not your issue....but thought I should mention it.
 

92 Sunbird LE

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Needs at least 12 volts to run properly.....as Mel pointed out...., check your harness where it goes into your firewall to the interior, mine was loose at one point, check all your grounds also(clean and shiney) engine ones too.


Doug in P.R.
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rstivers1989

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Hey Folks, thank you kindly for the responses.

The voltage # is coming from the OBD1 reader.

Voltage at the battery while running is 14.2-14.6, voltage at the Alternator is 14.2-14.6 while running (multimeter), with the OBD1 diagnostic tool its 10.2.

The harness was not loose, grounds appear to be good.

Where is the speed sensor connector?
 

92 Sunbird LE

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On top of the trans, passenger side, where the hole is on the pic, 2 bolts hold it on.

Doug in P.R.
 

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rstivers1989

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Hey there - sorry for the long delay in response here:

1) Speed sensor connector is fine
2) Coolant sensor is fine
3) Oil pressure is fine

Currently on the list to check IAC Voltage, maybe the connector is bad? It looked brand new and clean.
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92 Sunbird LE

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I would just keep running fuel injector cleaner or Seafoam to see if it clears up, or take out the computor and check the terminals to it and on it and take out the prom cover and blow it out with compressed air...

Doug in P.R.
 
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