Misfires

KYCSAILOR

MEMBER
VOLKSWAGEN

Hello, I have a 1999 Jetta AEG model. I am getting P0300, p0301, p0302, p0303, p0304. Car will not idle or accellerate. I have given it a complete tune up. New oxygen sensor, new intake gaskets, fuel pressure to factory specs, injector flow rate is good (removed and bench tested), compression excellent, engine vacuum is between 40-50 psi, no vacuum leaks found as of yet, new fuel filter and pump is working good. Ignition coil is in good order. Mass air flow sensor is clean and appears to be working. Electric air pump had become unplugged and car was ran like this for a while before it was notice. I only noticed this after I started having running problems. Plugged it back in and it seems to be working. I am stuck. Any sugestions? Thank you.

2 Replies

RASMATAZ

MECHANIC
75,992 POSTS

What you got here is a nightmare, you sure its not possesed. New O2 sensor/s are they OEM parts.

Misfires can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel.

A Random Misfire code usually indicates a vacuum leak or bad gas.

If a misfire in a specific cylinder should lead you to check the spark plug, fuel injector and compression