Cold start
 

I have a 1990 mercedes 300e 6 cyl, 3.o.
My car starts with great difficulty in the morning but,
starts normally thereafter. Please advise....

Paul

In my case it was a combination of some bad sensors (coolant, intake air temp) and the idle control valve. I also replaced a bunch of the rubber hoses to prevent vacuum leaks. After doing all that it starts up great and solved the issue.

With the possible exception of the new direct injection cars, all cars with gasoline engines require the concept of "choke" to start when cold.

"Choke" entails a richer than normal mixture plus some extra air to deal with this.

Richer mixture is required because the fuel in the fuel-air mixture tends to leave the flow and "stick" to cold manifold surfacese, i.e. not making it to the combustion chamber.

Extra air is required because the mixture still needs to be stoichiometric.

On older carb cars this was accomplished by a choke flap and a fast idle cam.

On your fuel injected car, it's accomplished by a cold start injector plus the idle control valve. Both of these are computer (electrically) controlled based on inputs from a temperature sensor (NOT the same one that feeds temp guage).

If the air quantity is affected by vacuum leaks, this will create a problem, too.

So, it's ECU, wiring, sensor, injector, valve, vacuum.

Of course the way to repair the condition is to understand how the system implements the fuel air condition when cold. Other than a cold start valve which operates for a brief time while starting the important issue is a combination of starting enrichment and cold running enrichment. The starting enrichment affect is accomplished with an approx 50ma control signal to the EHA. This is added to the approx 20ma cold running control signal to add up to a 70-80ma cold cranking enrichment signal to the EHA. A common problem is to find no enrichment signal at all due to a dead system due to a defective OVP relay.

So.............. the first place to look is at the EHA control signal.