Well, I had to go and fix something that wasn't broke, that'll learn me...

Alas, I have adjusted the throttle screw, and now she runs like crap.

I know there's a way to adjust the throttle switch (on other side of intake, that leads to the ECU), but do I need an ohmmeter? or multimeter? Or is there some Zen master mind trick I can use to get the switch back in tune with the throttle?

And, I f I drive it like this (out of whack) will I damage the D-jet system any?

I would be greatful for any help. Just please be specific, as I'm still learning after a year and a half of vintage volvo enthusiasm. (My girlfriend and I are getting married nonetheless, she says I don't have to give up working on the car, but she said some things are going to change around here...god only knows what...I imagine instead of taking the whole weekend to work on the car I may only have a few hours...uh oh)

Cheers,
samuel

Go to VClassics.com for a discussion and lots of troubleshooting guidance on D jet. You will need a volt-ohm meter to test the components. From your message, it seems like the throttle switch is out of adjustment or maybe worn or dirty. First set up the throttle so its completely closed at idle. The little stop screw should be positioned so it just makes contact with the throttle plate flange when the throttle is closed. Then use the ohm meter, as described in the VCLassics info to set the throttle switch.

I'll give it a whack...

On D-Jet FI you don't adjust the idle with the throttle valve. It should ALWAYS close fully, and the throttle switch should be adjusted so that as it closes it just closes the set of contacts in there (there are two sets - one closes when the throttle is opened to engage extra injector pulses - the other set closes at idle to engage the special idle circuit in the computer).

The idle is adjusted by a large forward facing screw underneath the manifold, directly underneath the throttle. You will have to take off the large air shose to the air cleaner to see this. Loosen the locknut and screw it in and out to set the idle. Some things that can hamper your ability to set idle speed:
1) Stuck Cold air bypass valve - this is the aluminum thingy attached to the block and attached to the manifold near the throttle by two inch thick hoses. When cold it is supposed to let more air through and raise the idel so it doesn't stall when cold. These often (OK - almost always) stick - either open or closed. If it sticks open you'll have a fast idle even with the idle adjustment screw all the way in. Stuck closed and it will die when old unless you keep a light foot on the accellerator. As a temporary fix (or permanent when you find out how much new ones are!) for a stuck open one just plug the hose.
2) Vacuum leaks - any leak anywhere past the throttle valve will raise the idle. Likely suspects are manifold gaskets, injector seals, and faulty brake boosters. If they let too much air in the idle will be too high no matter how much you fiddle with the idle adjustment.

If your car is still running funny it could be another problem - luckily for you D-Jet is one of the simplest FI systems around and you can check it out pretty easily with a multimeter if you know the proper readings for each sensor ( http://www.icbm.org/erkson/ttt/engine/fuel_injection/d-jet.html ). Just remember to set the timing, adjust the valves, clean the plugs, and possibly even check the compression before starting to diagnose FI system problems. And another good tip is to consult a wiring diagram and check the sensor readings at the big multiplug that goes into the computer - this will check the wiring too - which is about 1/2 of the faults a D-Jet will get. If it checks bad there check again at the sensor to determine if it or the wiring is causing the problem.

Don't be tempted to throw in the towel and put carbs on - D-Jet works better than they do - it just requires a different skill set to keep in tune.