PeachParts Mercedes-Benz Forum - View Single Post

psfred · #4 02-09-2004, 03:07 PM

Dave:

Welcome to the board! Still making beer?

Sounds like the idle control valve is going wide open instead of closing if you get faster idle by plugging it in -- it should fail open unless really dirty.

You can clean it by spraying carb cleaner in it and shaking with the hose nipples covered, repeating until the fluid comes out clean.

Check the hoses on the idle valve too -- the ones on the TE were rock hard and leaking. Pure b,...h to get the one on the mainfold back on with the clamp, but the car runs much better.

Yes, 18V would probably fry the electronics, but if the OVP is working, all the sensitive stuff should have been switched out at high voltage -- that's what it's there for!

If you have not done so, replace ALL the rubber vac line connectors -- chances are they are all shot and leak like crazy. I did them all in the TE, cured the hard shift, throttle lag, and most of the rough idle.

To check the duty cycle, you want to put the red lead of you frequency meter (set to read duty cycle) in pin #3 of the diagnostic socket on the EZL computer (driver's side fender) -- socket has a round screw-on cover. Black lead in #2 or ground, or free like for my cheapo Sears meter that won't read at all if the black lead is grounded. With the O2 sensor hot, duty cycle should be around 50% and changing. If it's always 50%, the O2 sensor isn't working, if it's high or low and changing, mixture is out, if not 50% but constant, some electronic problem. Make sure you're not set to frequency, as that is constant. You can cheat with a digital VOM and read voltage instead, but it's not as accurate -- you'll have to check with another car to see what the meter actually reads at 50% duty cycle -- should logically be 6V, but I don't think it actually works that way.

If you have a direct reading mA meter (not an indirect one, you must complete the circuit) you can check the current to the idle control valve. If the current is high and the speed is high, either the speed signal is bad or the control circuit is toast. If should be very low above idle, then swing up and then steady when the idle speed is being controlled by the valve.

Current to the EHA (back side of the fuel distributor) should be near zero at 50% duty cycle. 20mA key on, engine off, should go positive when the throttle is opened, then rapidly return to aroun 50%.

Fix all the vac leaks before attempting to set the mixture.

You probably need a new belt tensioner, too -- the "spring" is the rubber bushing in the tensioner (like the rear suspension links) and they usually go bad in place. Work OK until you loosen them, then refuse to properly tension the belt when you crank the screw down.

Peter