1993 Elantra Idling Rough

Good Day,

1993 Hyundai Elantra 250kms, 4 cylinder, 1.8L engine, 5 Speed

Just out of the blue one day the car idles very very rough upon starting. It
revs up and down between 1500rpm and 1000rpm. When it is fully warmed up the
idle speed variance drops to between 1000rpm and 750rpm. I did a full
tune-up, gas filter, PCV valve etc, with no effect.
Mass air has been checked, throttle body cleaned.

I took it to the local garage and they ran some tests and stated a burnt
valve ?? The compression test shows 190psi for all 4 cylinders.

Any ideas ?

Thanks.

 

If you've got compression, you don't have a burnt valve. It sounds like
the garage you took the car to is either incompetent or dishonest.

On a car that age, the first thing I would do is to systematically check
all the electrical connections in the engine bay. Corrosion is likely,
particularly on grounds. This may or may not be your problem, but it's a
good idea to clean up any corroded connections anyway.

Have you checked the output from the computer? It can be done with a
voltmeter, or you can take it a dealer and have them check it. That will
probably point you in the right direction.

 

Is it misfiring or simply raising and lowering the idle?

If it's the latter, look for an improperly adjusted idle switch (the one
terminal switch on the throttle body -- switch is closed at idle, open if
accelerator is depressed a little bit or more) or a bad idle actuator.
Check for coolant leaking into the throttle body.