Hi guys,

I woulds like opinions here please. This is my daughters car and I am working on it. It originally would lose power then die. It would start back up and get her home after letting it sit for 20 or 30 min. A few months later it died and wouldn't start at all. I towed it to my house. Checked for fuel and spark, both seemed O.K.
.
Here is a list of what I have replaced so far:
Used engine from same model and year Quest from junk yard. (nice and clean inside engine)
fuel pump - new
fuel pressure regulator - new
mass air flow sensor - used
main computer (ECM) - used
pcv valve - new
spark plugs - new
spark plug wires - new
cap & rotor - new
all vacuum hoses - new
all fan belts - new
all rubber fuel lines - new

I have ran the following tests from the factory service manual and they checked out O.K.
ECM input output test
camshaft position sensor test
mass airflow sensor test
ignition coil test
power transistor test
fuel pump test (electrical) I haven't checked fuel pressure on the new pump yet
closed throttle position switch test
throttle position sensor test
IAC valve-AAC valve test
IAC valve-FICD solenoid valve test
ECM relay, fuel pump relay, IAC relay-FICD relay

I have also cleaned every electrical plug under the hood with a tiny wire brush and lacquer thinner when I had the engine out. then sprayed them with electrical component safe solvent and checked for loose connections and tightened every one.
I put on an extra ground strap from the battery to the chassis and from the engine block to the chassis.

Well, I think that's where I'm at.
Everyone's thoughts on this subject are appreciated.

Thank you - Ric

Update

There is an idle speed adjusting screw on the "IAA" or idle air adjusting unit, which is made up of the IAC valve - AAC valve and the IAC valve - FICD solonoid valve. This adjusting screw was turned all the way in. I unscrewed it 6 turns to match the position of the old one and now the quest will idle. The idle is rough and will run at 800 rpms for 5 seconds then run at 1400 for 5 seconds and keeps going back and forth between these two. I can hear a vacuum leak somewhere under the intake manifold. It seems to be coming from the bottom end of the PCV hose where it connects to the valve cover.

P.S. - On sat Aug 13 I took the fuel rails and the injectors out and cleaned them and bench tested them they were not that dirty but now they are like new and work good. This changed nothing. The car still would not stay running. Oh well, at least I know they are like new.

Everyone's thoughts on this subject are still appreciated.
Thank you - Ric

Update

The original problem of won't start seems to have been the distributor. It has photo sensors in it which tells the computer to send a signal to the injectors to squirt gas into the cylinders. This was fixed by removing the distributor and taking it apart enough to be able to spray it with carburetor clearer to clean the photo sensors.

The idle fluctuation and hard start was difficult to find the problem. It seemed to be a vacuum leak, but... I had already replaced every vacuum hose. yesterday I tracked down the vacuum leak to a faulty (NEW) gasket that was installed between the intake manifold and the EGR valve. I made a new one (don't trust store bought) (out of a extra thick manila folder) and used permatex hi-temp copper silicone on both sides of the gasket.

I read a post where a mechanic explained how to find a vacuum leak. Use carb cleaner spray while the engine is running to spray hoses and connections, when you hit the leak the engine will smooth out. This was a great tip and worked very well.

The van is now fixed and running fine.