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I recently put my 2002 Nissan sentra 1.8 back together from a head gasket job.  Upon starting the car, it idles just fine...but as soon as I put it in drive the rpms drop to about 550 and feels like it's about to stall.  Giving it gas smooths every thing out, until I go over 3000 rpm or if I press hard on the accelerator, which both send the car into a fit of shuddering and making backfiring-like noises until it stalls completely.  I also notice that my gas pedal is tight, or hard to depress.  Any ideas? 
Note: I've read that my maf sensor may have something to do with it, so I unplugged it, ran the car for a while and that just made it worse.plugging it back in brought the car back to "normal"...

Edit: I'm gonna run through that list of possibilities that zipzit provided and check back which the results.

  • Swapped spark plug wires? One wire / spark plug not seated correctly?Cam shaft alignment to main crankshaft off by one notch on gear? – zipzit Feb 1 '18 at 4:41
  • Funny you mention the camshaft being off by a notch because this is what I suspected it could be...but why would it only be evident when in gear? – Nathaniel Davidson Feb 1 '18 at 5:13
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    Really? What do you think the cam shaft does? Timing matters. its not possible to simultaneously breath and drink water. Human: Breathe, then drink, then breathe. Engine: suck in air/fuel, compress, ignite & explode, evacuate exhaust. How did you ensure Top Dead Center (TDC) alignment for the camshaft when reinstalling the engine? Can you insert a photo of the page from the repair manual you used into your question? – zipzit Feb 1 '18 at 5:51
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    @NathanielDavidson . What service book are you using? Haynes or Chilton? If you didn't use a book or some other reference guide to exactly tell you exactly how to line up the cams with the crankshaft at Top Dead Center, you may well have gotten things out of alignment. There may be some youtube stuff out there, but I'd sure start with the book. – zipzit Feb 1 '18 at 12:56
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    I do see this link from Autozone that may be helpful. Perhaps you used this instead of a book? Remember the Cam shaft spins at half the speed as the crankshaft. You will need to understand how the valves work to ensure you are in a compression stroke. – zipzit Feb 1 '18 at 13:03

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