87 bonneville

I really hope one of you guys can help me with this.....
The problem started on a typical day of stop and go driving in town. It
started running really rough at low rpm's, I had to keep the gas pedal half way down to maintain high rpm's and keep the engine running, however once up to 35 or 40 mph would seem to run ok, but let off of gas and engine would die. Mechanic said it was the catalytic converter($175), so I had it replaced, then he said it was the oxygen sensor($60), replaced that also. Now a week later, I have had the fuel injectors replaced ($300), the throttle position sensor($40), fuel filter($10), plugs and plug wires($45) all replaced. Six months ago I had to have the coil packs replaced, and shortly afterwards one of those went bad and had to be replaced a second time. I am at a loss here, the car seems to load up with gas and flood out once it becomes hot and the thermostat opens, when restarting you have to press the accel all the way to the floor and let it burn off the excess fuel before it will attempt to go anywhere, and when doing that it blows black smoke out of the tail pipes not really bad but noticable. The car has 186,000 miles original motor, and has been maintained very well....so what gives? Any help will be greatly appreciated.......
Thanks in advance, Brea
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87 pontiac bonneville 3.8L V-6 FWD

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Brea wrote:

While you seem to be getting more than fair prices, is this mechanic actually testing anything or just throwing parts at it?
Many stores such as Pep Boys and Advance Auto Parts can test components in-store before you buy a new part. Going by the conditions you describe, I'd recommend bying a Noid Light kit. http://tools.batauto.com/index.php?crn …&rn4&action=show_detail $22.99 and it can really help in whittling down what is and isn't wrong.
I am at a loss here, the car seems to load up with gas

You might see if you can pull up any trouble codes.
Codes for GM Car Computers - Test Your Car
CODES USED BY COMPUTERS IN GM CARS
New cars use computers to store and remember malfunctions that occur. These are displayed in the flashing sequences in the instrument cluster. A typical sequence of instructions follows:
Locate the C3 diagnostic connector (also called the "ALCL"). It is usually under the dash on the drivers side. On the Ponitac Fiero, however, it is located in the console between the seats. Short the 'A' & 'B' positions of the diagnostic conector ('B' is ground), then turn the ignition key on but do not start the engine. CHECK ENGINE OR SERVICE ENGINE SOON light on dash will flash out the number 12 ( flash - pause - flash flash ) which means the self diagnostic mode is working. This will be repeated 3 times. Any trouble codes the computer (called the Electronic Control Module or ECM) has stored will then be flashed out ( for example: code 23 is ( flash flash - pause - flash flash flash ). If more then one code has been stored, they will be flashed out in order, each repeated 3 times. Look up the code in the following chart to find the faulty circuit or component.
NOTE: Do not automatically replace a component without first checking its wiring and connectors. Also, it is good practice to test the component further using a digital volt/ohm meter as described in the vehicle's service manual. Remove the A to B short and turn off the ignition. After the repairs, clear the trouble codes from the computor's memory by disconnecting the fuse marked 'ECM' for at least 10 seconds.
C3 TROUBLE CODES
12- Normal code with ignition on and engine off. Indicates no distributor reference pulse to ECM. Not stored in memory. 13- Oxygen sensor or it circuit 14- Coolant Temperature Sensor circuit shorted. 15- Coolant Temperature Sensor circuit open. 21- Throttle Position Sensor (TPS) or its circuit. 22- Throttle Position Sensor circuit voltage low due to grounded circuit or faulty adjustment of TPS. 23- Mixture Control (MC) Solenoid circuit open or grounded. 24- Vehicle Speed Sensor (VSS) or its circuit 32- Baromteric Pressure Sensor circuit voltage low. 34- Vacuum Sensor or Manifold Absolute Pressure (MAP) circuit. 35- Idle Speed Control (SC) Switch circuit shorted. 41- No distributor reference pulse to the ECM. Unlike code 12, this will be stored in the ECM. 42- Electronic Spark Timing (EST) bypass circuit, or EST circuit open or grounded. 43- Electronic Spark Control retard signal for too long a time. 44- Lean exhaust 45- Rich exhaust 51- Prom (programmed read only memory) calibration unit faulty or improperly installed in ECM. 53- Exhaust Gas Recirculation (EGR) valve vacuum sensor has received improper vacuum signal. 54- Shorted Mixture Control Solenoid circuit and/or faulty ECM. 55- Grounded Vref (terminal 21), high Oxygen Sensor circuit sensor voltage, or faulty ECM.
(from; http://www.totse.com/en/bad_ideas/scams_and_rip_offs/gm_codes.html )
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He was running the computer and nothing was coming up, turns out it was the Mass Air Flow Sensor....something he had changed about 4 months ago...

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