Muti Codes due to CEL

I bought a 1998 Passport 2 months ago it has 186,000. I have replaced a lot of sensors in the last 2 weeks. Specficaly the TPS, all 4 O2 sensors, Idle Air Control Valve, Manifold Air Temperature Sensor, and EGR.

I'm still getting the following codes..

P0405 Exhaust Gas Recirculation Sensor A Circuit Low...intresting since I just replace the EGR valve yesterday. I also tried to clean the EGR tube in the manafold as it was not horrably gunked up but I cleaned it as best I could with SEAFOAM and Carb Cleaner. I'm sure i could keep working on this to make it cleaner.

P0327 Knock Sensor 1 Circuit Low Input (Bank I or Single Sensor)... One of the sensors i have not replaced so it is now on the list.

P0102 Mass or Volume Air Flow Circuit Low Input.... I cleaned this also but how can i check to see if it bad?


Thanks in advance.. Many posts on this forum have solved other issues I've had already.

None of these codes automatically means that the mentioned sensor should be replaced.

Any suggestions on how to check the actual sensors to see if they are good? All thye harnesses appear to be in good shape.

You really need a service manual. It's too much to get into here. There are troubleshooting steps that are outlined in a service manual that will help. Or, you can google each code and usually come up specific information. Don't worry about manufacturer, the codes are standard for all cars.

Bought a brand new Delphi EGR and it was faulty. Might want to verify it's good. I went months with the code, cleaned everything and could not get rid of the code. Finally swapped a different working egr and voila.

FYI.. Exchanged the EGR yesterday and I was able to go 1 full day before the EGR code came back... the investigating will continue.

FYI... CEL and EGR low voltage code.... Thought I'd try something new.

I took the connection plug off the new EGR and "tighted/pinched" the female connectors with a small screw driver. After reinstalling the plug the CEL was off. It satyed off for about 5 mins of driving and satyed on while I ran errands for 3 hours... only to turn it self off 5 mins before I got home.

Still stumped.