I( can'r win.. Starting issues

There is no choke on a fuel injected engine.  This 1985 - 1986 generation 928 uses the first generation of digital fuel (LH) and spark control (EZF).  The air/fuel ratio are managed by:

1. A presumed fuel pressure.  The system requires a precise fuel pressure to operate.  Also, the fuel pressure regulator and/or damper can leak unmetered fuel into the intake manifold causing an over-rich air/fuel ratio.

2. Coolant Temperate sensor (AKA Temp II sensor).  Both the LH and EZF modules obtain engine temperature from this single sensor.  If it reports the wrong temperature (it has a reverse coefficient of resistance), The fuel injection system may inject the wrong amount of fuel for the existing engine temperature.

3. Mass Airflow Sensor (MAF).  This system uses a hot wire heat and control to provide an accurate representation of the mass of air flowing into the engine.  The LH injection module uses this measurement to calculate how much fuel to inject.  A failing MAF can result in too little or too much fuel to be injected.  The hot wire glows red after each driving cycle to clean off contaminants.  After a few decades of use, the resistance of the hot wire changes and the MAF drifts out of calibration.  Replacing the MAF is a normal service item and should be tested every 60,000 to 80,000 miles to verify proper operation.

4. Fuel injector flow: A leaking or improper spray pattern can result in improper running.  The fix is to clean them and have them flow tested and replace if necessary.

5. LH Fuel Injection module: this computer takes in all the inputs and calculated the exact fuel necessary for the engine temperature range and power demands.  If it fails, it normally doesn't work at all or injects the improper amount of fuel.

A qualified mechanic can diagnose failure in these items.  The operation of the LH and MAF modules can be tested and repaired as needed.

Where are you located?  Someone may be able to suggest one.  I can imagine a mechanic familiar with mid 1980s European cars may understand this generation of Bosch engine control systems.  Volvo and Saab used similar systems.
 

The closest shop to you that I've interfaced with is Top Auto located SW of Charlotte in Indian Trail. There are very good shops Digital Chassis in Durham, NC and Howard Wright in Atlanta, GA.  

These may be too distant.  So I suggest that you call local independent shops that work on older Volvos or Saabs and ask if they'd take a look at your 928.

 

A US-Spec 1982 Porsche 928 has the L-Jetronic fuel injection system.  It is analog system, not digital.  The spark system is a simple transistorized triggered unit off an Hall effect sensor in the base of the distributor.  The air/fuel ratio is set at a vane-type airflow sensor.  It has mechanical elements to it that can cause problems too.  A flooding out over-rich condition to me sounds like a leaking fuel pressure regulator/damper or leaking fuel injectors.  However the L-Jet injection module could also be failing.  Hard hot start can be caused by fuel flooding in when the engine is turned off.   Also if fuel system is not holding pressure, the fuel in the lines can vaporize causing vapor-lock (a more common problem on older cars).  There is a check-valve in the fuel pump that can allow pressure to leak-down. There are factory workshop manual with a lot of information.  The older L-Jet systems are quite reliable however in 43 years components can fail.  In my opinion the only way to find and fix the problems is a complete check-out system by system.  Likely most of the rubber hoses and components need to be replaced due to age.

There is a Temp II sensor that should be check out.  Also, the L-Jetronic fuel injection uses a cold start valve.  See this document for specifics.   

The  issue is if the Temp II sensor indicates a cold engine when it is actually warm, the ECU "thinks" the engine is cold and will inject too much fuel.

Look at the previous document that I posted, all the information is there.