QuestionQUESTION: First, the car was idling high (over 15 rpm) and then I changed the air slider. For a week or two, it was perfect. Then there were problems with the hazard wires and the car started to idle low (below 5 rpm) and hesitated. I replaced all air valves and hoses. I don't know what could be wrong with it? I just ordered a Mercedes R107/W126 idle control unit. Do you think this could help? Any input on how I could fix this problem would be great. Thanks!
ANSWER: I assume this is a cold engine issue, read the following
Idle Bad with Cold Engine
1. Leaks in air intake system:
Check all air intake and vacuum connections. Any old hoses must be replaced.
Be sure to check the intake boots around the intake runners. Check all hose clamps.
Replace any collapsed hoses.
2. Auxiliary Air Valve does not open:
Check the hose connections to the valve. If these check good remove the valve and
check for leaks by closing off one end and applying a small amount of suction to the
other end, if air can be drawn through the valve, with the other end capped off,
replace the valve.
3. Cold Start Valve leaking:
Remove the cold start valve, located in front of the intake. Leave the fuel line connected,
place the valve over a container, disconnect the electrical connection, apply 12 volts
to one of the connections, apply a ground to the other side, look for an even conical
spray pattern, turn the power off, wait a few seconds, there should be no leaks. If
the pattern is not correct or the valve leaks, replace the valve.
4. Cold control pressure not correct:
Check the warm up regulator. I would look for a pressure of at least 1.25 -1.50 bar
(18-22 PSI) at freezing temperatures. Be sure to check the pressure coming from the
mixture control unit.
If the pressure is not correct, do a complete check of the warm up regulator.
5. Injector Leaking:
The opening pressure could be to low, opening pressure should be around 2.5-3.6 bar
(36-52 PSI). Check all the injectors for evidence of leakage. Test for opening pressure.
When you reinstall the injectors be sure to replace the o-rings.
6. Injected Quantities low:
Compare the fuel quantities of each injector. Place each injector over a container and
record the amount of fuel each produces at a given amount of time. They should be equal.
7. Basic Idle incorrect:
Check and rest the idle per the specifications. It is best to set it when the engine is warm.
Check the co output, also.
8. Fuel Leaks:
Inspect all fuel connections.
9. Fuel injector Clogged:
Pull the injectors and inspect for correct operation. Apply power to the fuel pump,
jump the wire terminal numbers 30 and 87a. Caution fuel will flow from the injectors
when the air flow plate is moved in an upward direction. Check for correct operation.
10. Control Plunger in the fuel distributor binding:
Remove the air cleaner and carefully move the plate up and down, do not force the plate.
If it binds investigate. If it is not simple to repair replace the unit.
11. Idle speed, Ignition Timing, and mixture out of tolerance:
Check and adjust all of the above.
12. Faulty Ignition System:
Check the ignition system. 1973-1977 check point gap .016,Condition of cap and rotor,
---------- FOLLOW-UP ----------
QUESTION: Dear Ron,
Sorry I was not explicit enough. This problem occurs when the engine is warm and I put it in drive. It goes from 6 or 7 rpm to under 5 rpm. The hoses and the accellerator air valve has been replaced. Also, there is a humming noise on the low drivers side belt. Can you help? Any other ideas? Your imput so far has been great.
Thanks
Jim
AnswerOK - first make sure all adjustments are to spec - plug gap, point gap, timimg
then to set idle
adjust height of aairflow sensor plate - it sould restjust below teh upper edge of the airflow sensor venturi
Center the air flow sensor plate
Adjust minimum air - warm engine then shut off, inspect AAV to make sure it has closed completely
restart engine - close the idle air pass and adjust throttle stop screw so the engine barely idles - about 450-500 RPM then use the manual adjustment on the idle air pass to set curb idle at 950rpm
setting CO is next - if you dont have a meter its just a guess, buit remember very SMALL adjustments make a big difference
humming is probalby fuel pump - which is OK
