1993 Hyundai Elantra, Idle problems?

Question

Vehicle has a 1.8 16 valve DOHC. When idling, it slightly revs up and down and up and down repeatedly. What could be causing this? Please..........reputable mechanics or Hyundai techs answer please. I do believe this is beyond the knowledge of the backyard mechanic.

ok, no vaccum leaks, no hissing noise heard. Still accepting answers for possible problems

Ok, the crankshaft position sensor has nothing to do with this idle problem. I do have pretty good knowledge of today's car systems. but this particular problem has baffled me, Im still taking answers from auto techs that knows a Hyundai pretty good.

Answer 1

idle air control motor probably

Answer 2

Idle air control is correct



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Answer 3

The intake manifold gasket is cracked inflicting a pretend air signal affecting gas injection and engine timing. seen it many cases. replace the gasket and situation is solved. Spraying carb purifier round searching for an air leak gained't locate the issue yet brake purifier will - it has propane as a propellant and makes the engine react even as the better gas is going into the engine. solid success.

Answer 4

A dirty crank shaft sensor ,or Mass Air Sensor(MAS)can cause what your vehicle is doing.Don't under estimate the little guy some of them trial and error alot of time and money solving problems like yours.good luck.

Answer 5

That sounds like a vacuum leak to me. listen for hissing under the hood. could be a cool snake.

Answer 6

Your timing needs tuning.Just go to any workshop and the job will be done.