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Discussion Starter #1
I have a 1993 MK3 that I just bought about two weeks ago.
I have a wide range of knowledge of cars but am completely new to VWs so I'm a tad lost.

I know my o2 sensor needs to be replaced.
The car was bogging really bad at low RPMs. I cleaned the master air flow sensor and that helped bring the idle up. (it was initially idling so low the car would just shut off)

The car started bogging again. Also, the second you let off the gas the RPMs drop to zero and the car shuts off.

Went to start it up and it started but the RPM quickly dropped to zero, shutting the car off. Went to start it again and it wouldn't turn over.

I know the bogging issue was due to the bad o2 sensor, but can that get so bad that it will cause the car to not start?

I was planning on getting the cat and o2 sensor replaced next week.
 

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Discussion Starter #2
oh and I'm wondering if it may have to do with the IAC as well. I've heard of those being cleaned out with carb cleaner and that helping. Opinions?
 

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Yeah if they are bad enough they will make your car not start. The IAC valve could be cleaned with carb cleaner, its a valve that gets clogged up after awhile. Who knows if it actually helps.
 

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idle air control valve allows correct amount of air that engine needs when idleing to keep air to fuel mixture where it should be so if its clogged or dirty it very well could keep it from idleing or cause a spuratic idle
 

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however the oxygen sensor will not cause the car to not idle or start. all the oxygen sensor does is "sense" the levels of oxygen and fuel that is in the exhaust system. if it senses to much oxygen (lean mixture) it sends a signal to the ecm to dump more fuel to equal out the air fuel ration and if it senses to much fuel (rich mixture) it tells the computer to cut back on fuel to adapt to the correct air fuel mixture. i have ran around with no wires connected to my oxygen sensors and had no idle or drivability issues except for a decrease in fuel mileage. This being said i do not recomend cutting your wires or ignoring that they need replaced because over time if you continue to run your vehicle on a rich mixture it could cause "wash out" of piston ringswhich in turn could result in premature engine failure, but again this would take years to do not something that could happen overnight.
 

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Discussion Starter #6
Thanks guys, much appreciated.
I had to take it to work today and it started up just fine and drove great to work.
On the way home though, I ran into a new problem. It started to do its usual bogging, but much harder then the gas pedal did absolutely nothing. The car was still on but no matter how hard I stepped on the gas, it wasn't registering.
The car shut off. I turned it back on and it was back to normal and driving ok again.
I'm praying this is because the o2 is just THAT bad and maybe the computer's just not sending any fuel to the engine at those points..
But I've never dealt with an issue like this in a vehicle before. :(
 
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