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Old 10-31-2014, 02:37 PM   #1
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Default GM 3.4 high rpm, won't drive

Car:
2003 Pontiac Grand Am 3.4 V6

Problem:
Engine starts fine, then races between 3600 and 3800 RPM at a steady twice per second. Engine dies immediately when I attempt to shift into gear. It displays the security light and a P102 (MAF low freq) code. Disconnecting the MAF gets rid of the code, but no change otherwise.

I'm going to test the MAF and replace if bad, but I'm concerned something else is wrong.

Any suggestions?

Background:
I've done a lot of work on this engine, so I could have messed up nearly anything.

I had a 'start and die' problem. I replaced the fuel filter and pressure regulator which didn't help. That problem was fixed by hard wiring a resistor between the ignition switch and the BCM, then doing a 'relearn'.
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Old 10-31-2014, 02:51 PM   #2
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High rpm like that could be a vac leak, bad IAC/PCM/harness, stuck throttle plate open(crud in bore, kinked throttle cable), etc.
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Old 11-01-2014, 10:52 AM   #3
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I agree. Bad vacuum leak could be caused by leaving a hose off or a sensor on the manifold or the iac ,etc
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Old 11-01-2014, 01:01 PM   #4
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Default Thanks guys!

I will certainly check for leaks and lose connectors. It'* great to get a response so quickly! Let me add some more details.

I get no response to the gas pedal, the engine cycles smoothly between 3600 and 3800 like it'* hunting for something.

The engine dies immediatly when I move the gearshift, it'* clearly an electronic command. That might be a normal safety feature I suppose, it'* probably not a good it idea to shift a racing engine into reverse.

I checked the MAF freq. I got 1020 -1040 Hz, following the rpm cycle. That seems to qualify as low, but it is following the rmp change. I'm going to remove it and inspect/clean it.

Finally, I ran the engine with a different PCM in it. Before I discovered the ignition switch problem, I tried changing the PCM. I got one from pick n pull, same year and model. It didn't help, so I changed back to the orginal. I'm wondering if there is some 'relearn' the PCM needs since the engine was cranked while it was absent.

I read about a CASE relearn for the crankshaft sensors. That seems a likely problem, but the symtoms don't really match. This car runs, but won't drive at all!
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Old 11-01-2014, 01:24 PM   #5
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Have you done anything with the TB or TPS(throttle position sensor)?
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Old 11-06-2014, 04:10 PM   #6
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Default TBI

I think I had the TB loose. I'll check the TBI connector. Thanks
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Old 11-17-2014, 11:22 PM   #7
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Default no signal or power from TPS

Sounds like your TPS went. Need to make sure you are getting power from the TPS. There will be a voltage drop and gain when you move the TPS. If not you found the problem. You can find a vacuum leak using a cigar. Disconnect the main vacuum line and blow smoke from the cigar into the line (with the car not running). Watch to see where smoke comes out.
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