1.9TD (D4192T) electrical(?) problems

[voivoi]

First, pardon my English.

It's a 1999 S40 with the 1,9TD with almost 350 000 km on it. I got it about a year ago with a blown head gasket. I replaced that (got the head machined too) and a bunch of related parts, water pump, belts etc. Turned out that the gasket wasn't the only problem.

It starts up nice hot or cold, but doesn't run right maybe half of the time - or more. And when it doesn't it hunts on idle and jerks a little when driving. And it seems to be totally random. Another problem I noticed in the autumn is it sometimes does't seem to be responding to accelerator pedal. So it first runs ok, but suddenly, often when changing gears, it just won't accelerate properly until the revs get up to 2200-2400 and the turbo kicks in. After next gear change same thing. Or sometimes not.

Also occasionally there comes a horrible rattling or knocking noise. I can't really describe it, but somehow I think it might be related to timing. I think it's the same sound I once created by pulling a connector (maybe green) by the feed pump while the engine was running. When driving, the sound stops when I lift my foot from the pedal. Also the triangular warning light with lambda symbol lights up quite often even when there seems not to be any problems.

I've had the codes read two times now months ago. They gave the same result and in between I changed the EGR valve (the dealership said it was faulty, I was quite certain it wasn't after cleaning and testing and blocking, but I happened to get one for a reasonable price so thought to try anyway). I also changed the solenoid valve controlling the actual EGR valve with no success. But the codes. The second time it was a Bosch reader and it gave some descriptions in Finnish, too. I don't know how accurate they or my transalations to English are, but here goes:

EFI-122 Air intake temperature sensor; Impulse too high
EFI-235 Exhaust gas recirculation adjustment; Impulse too low
EFI-732 Accelerator pedal position sensor; Impulse too low

I think that in some more detailed description it said "impulse ratio" and when driving the EGR adjustment didn't get any higher than 40%. This is also what the mechanic at the dealership said and what he thougt to be an indication of a faulty valve. Btw, he hadn't worked on this engine type ever before.

I've done my best to test the AIT and APP sensors with a multimeter but they seem fine. I've also tried to find vacuum leaks and broken wires, changed vacuum hoses, checked connectors and pretty much everything I can think of. Battery seems fine, too and on idle it measures 14,4 V on the terminals. I'll have to check the alternator brushes on the charger, though. Anyway, I think it must be something electrical but I don't really know how to find it without spending too much money. And I don't want to do that.

I found a (partial) wiring schematic for year model 2000 but I think it's a little different. And it's missing some pages. Any help on that? Do those sensors and EGR solenoid valve maybe have a common grounding point or reference voltage or something?

Any thoughts?