This is a 1990 740 Regina NA with about 170,000 miles.

I've been investigating a rich smelling (eye burning) problem. It's real annoying when stopped and idling. If I drive for a distance and really really really get it warmed up, the problem seems to pretty much disappear, and out on the road it will still return 26-27 MPG. But for short distance, low-load driving, it's annoying as heck. I haven't found the right fittings to tap a fuel pressure gauge in to the rail, but since it still runs good and gets good MPG on the road, I am assuming the pressure regulator is OK - at least for now. Also, the replacement cat was still under warranty, so they gave me a new one even though the one on it "looked" OK - no change in smell.

Fault codes:

Socket 2:

3-2-1 Signal missing to/from Cold start valve. It throws this one IMMEDIATELY when running the engine for just a few seconds which I believe is expected on a Regina car that has been flashed for the cold start modification???

2-2-3 Signal missing to/from Idle Valve. I don't know how long it takes to throw this one. I do know that the valve corrects for cold idle, etc., so go figure....

Socket 6:

1-4-3 Knock Sensor signal absent or faulty. I don't know how long it takes to throw this om either. I do know that there is NO noticeable pinging and it always has good acceleration (for an NA 740). It DOES have significant cold engine knock, so I wonder if that is being picked-up by the sensor.

Now, I've been checking resistance across the various sensors, and here's what I've learned (Garage and engine block temperature are both in the mid-high 70's):

Air Temp Sensor - About 1800 ohms.

Coolant Temp Sensor - About 3700 ohms. (Shouldn't it be more like 1700-1800 ohms at that temperature?

MAP Sensor (labeled "GM")- pins A-B about 6000 ohms; B-C about 25,000 ohms; A-C about 1,000 ohms. Also, no matter how hard I suck on the vacuum hose, it has NO effect on resistance. I know I may not be able to suck neg 15 psi, but shouldn't I see "some" change?

My next step may be to put the temp sensor in warm-hot water and see what the resistance goes to.

OK, so now that I've bored you all to death, what thinks y'all?