97 toy corolla DTC po300 po301 po401 po402

PO300 and P1399 are random cylinder misfire detected.
PO301 cylinder 1 misfire
PO302 cylinder 2 misfire
PO304 cylinder 4 misfire
PO306 cylinder 6 misfire
I would say that you have damage to the ignition wiring harness or you ECM is failing.

Which code you have po300 or po301.po302 .PO301,PO302 will be coil or module.PO300 could be bad spark plugs,vac. leak,clog fuel filter,bad fuel pump,bad battery.

PO401: EGR insufficient flow detected
PO402: EGR excessive flow detected

A code P0402 most likely means one or more of the following has happened:

The DPFE (differential pressure) sensor is faulty and needs to be replaced
There is a blockage in the EGR (most likely carbon buildup)
The EGR valve is faulty
The EGR valve may not be opening due to a lack of vaccuum

P0171 is a lean code. Most common cause for this is a vacuum leak. The cat would throw a P0420 code. Don't mess with the cat. The P0300 code is a random misfire code. Look for a vacuum leak first.

There could be a hundred causes for a check engine light. First step is to hook up a computer scan tool and see what codes the computer has. The next step depends on the codes.

miss fire codes need to check tune-up, proper spark at all cylinders

Just change the air flow meter.Thats faulty.

make cranshaft gear has not spun under timing cover ive seen it happen before

Replace the coil pack.

Replace the coil pack..