Hi, I have the P0400 code on my 1997 Montero Sport LS with the 3.0L SOHC gas aspirated engine. I replaced the EGR valve and EGR valve solenoid, and only then did it occur to me that there was no need to do that, because all one has to do is put a hand vacuum pump on the EGR valve with the engine running, and if there is no change in the RPM, then it's pretty clear that the EGR tube or input manifold EGR tubes are clogged with carbon. And indeed, there was no change in the RPM at idle. The car didn't cough or stall, so I am assuming that carbon deposits are the problem, unless there's some other valve somewhere that stops the flow until the engine is going at faster revs.

Now I am faced with figuring out what to clean and how to get to it. When I take off the EGR valve, there are two holes underneath it. Presumably one is from the exhaust and one goes to the engine. How do I take apart whatever is necessary in order to clean everything and get the EGR flow to resume? The youtube videos on EGR cleaning that I have found all show later generations of the engine than mine. Mine has has the diaphragm-type EGR valve located near the firewall on the driver's side of the engine compartment.

Any help or advice would be greatly appreciated.