my low, rough idle, stall, hot /start solution: E320/300

[rvenerac]

Just want to share my experience and have suggestions on how to deal with this problem.
Recently bought a 92-93 E320 distributor type (not HFM/ no air mass sensor)
with the following initial problems

1. low and rough idle when normal T is reached with stalling at braking, creeping speed and wheel lock position
2. black exhaust fumes which I thought to be valve seal leak
3. poor mileage

Sequence of diagnosis
a. change to new spark plugs, cleaned rotor and ICV (but not tested) to no avail
b. with OVP or fuse removed, idle appears to improve but still rough and stalls
with fuse inserted, idle appears to decrease but still rough and stalls

c. tested ICV by applying 12V, clicks but not humming. When checked, it did not close fully and has an open gap. Borrowed an ICV from 102 engine, stalling partially improved
d. ICV change leads to hot and cold start problem which was engine dies and unable to maintain idle unless gas pedal is depressed for 10 sec. When engine is turned off or stalls, engine will not maintain idle once started unless gas pedal is pump. (possible causes listed using my vw Bentley:
Fuel check valve, fuel accumulator, leaky cold start valve, CTS, low air flow adjustment)
e. as a diy person and pressed for time and money, I planned to have the the
fuel check valve and cold start valve change and by grace of the Lord,
check valve is not available, check with other shops until I was directed
to the MB dealer on a late Saturday morning when the mechanics is about
to go home early that day. A fellow mechanic told me that the person
assigned to me is good at fuel injection

Because to much joy and saved money, I have to tip them and additional $50. I saw the trick on how did it. He first adjusted my CO by a hex wrench clockwise to increase the idle, then borrowed an OVP from another car and tested it. SOLUTIONS:
Changed OVP and adjusted CO idle with aircon and on wheel lock position. Cleaned my bosch spark plugs and noted black soot and code G8, according to him, 6 cyl prefers plugs with code F8 or F7. Cleaned the plugs and the black soot is due to fuel mixture and wrong plugs (G8 is for 102 engine) and not valve seals. He suggested to change my ICV and its tubes (cracked) to specs but temporarily he added an additional idle to compensate until I can change my ICV. He also noted that my Fuel Pump Relay is run continuosly by an ICE CUBE and suggested returning it to SPECS.

When driven home, stalling problem solved but when driven on highway I noticed some shifting delay and would not increase speed to the desired: VACUUM LEAK.
Solution, change the small tube connecting the fuel pressure regulator to cylinder head breather hose-air filter system. RESULT: FLAWLESS ACCELERATION and IMPROVED MILEAGE: TOTAL COST: $ 100-120

SAVINGS: Valve seal job, cold start and fuel check valve change.

BASED ON MY EXPERIENCE AND WITH HELP OF AN MB MECHANIC, I suggest the ff sequence of diagnosing low idle and stalling
1. routinely check rotor and plugs and change if necessary. Plug wires if defective, will involve only one and same cylinder repeatedly.
2. remove and check ICV if it closes tightly when current is applied, change if defective. Reattach ICV and check tubes for leaks. then
3. I WOULD SUGGEST CHANGING OVP FIRST BEFORE GOING TO STEP 4 (even if it appears to be good like mine)
4. ADJUST CO using hex wrench counterclockwise until desired smoothness ia attained to richen fuel (this will elevate the air/flow plate to increase fuel flow)
5. check idle with both aircon and wheel lock position and further adjust CO
6. check for leaking vacuum tube from fuel pressure regulator to cylinder vent. Seal tightly.

ACCORDING TO MECH, cold start valve and fuel check are not prone to be faulted but
As STEP 7, you can now check for low fuel pressure problem due check valve by turning off the engine for 30 min to 1 hr and restarting the engine without pressing pedal. Normally, engine will start w/o pumping for gas.

FUEL PUMP RELAY REVISIONS: since fuel relay model of my MB is very different from those available. (I think my car is hybrid 103 and 104 engine, I am looking for a wiring diagram and plan to revise my FPR, FPR usually runs for 1-2 secs and cut off is electronically controlled. My options are,
1. to try to run it through starter switch (terminal 50 or 15 from ignition switch)
2. or to add a timed control using the cold start system or thermoswitch
or a timer like those that control glow plugs in diesel engines.
ANY SUGGESTIONS?

[sbourg]

Replacing the vent tube from the fuel pressure regulator should have no effect on engine function. A bad one will simply allow unfiltered air to enter the closed system, and fumes to escape. My guess is you disturbed something else in the process. Check for hardened and cracked idle circuit hoses - they are thicker, rubber ones, and a vacuum leak here will cause improper metering by the airflow meter.

Steve

[rvenerac]

this tube attached to the intake manifold (based on my vw golf manual) uses the changes in vacuum in relation to engine load to increase system pressure. with leaks it causes sluggish acceleration and AT shifting and high fuel consumption due to sluggishness because you need to floor and pump the gas hard
to accelerate.

[sbourg]

I don't know anything about your Golf, but the tube in question should not go to the intake manifold - it should go to the breather from the valve cover. As you know, there should be no significant vacuum at this point.

In order for the pressure regulator to function, the 'backside' of the regulating diaphram must be at atmospheric pressure. This is the purpose of the vent port. If the diaphram ruptures or leaks, though, you would have fuel pouring over the engine. So, it is routed instead into the vapor recirculating plumbing.

The pressure regulator itself is just designed to maintain a constant, high fuel pressure. There is no loop control there. The CIS injection modulates pressure and thus flow rate at the fuel distributor, mechanically coupled to the airflow meter underneath, and electrically fine-tuned via the EHA valve by the fuel injection control module, using loop inputs from the oxygen and other sensors.

Steve