Airflow sensor questions/hard start 1986 190e

[bbarcher]

Hello, I have a 1986 190e 2.3L 5-speed. The car runs well and starts up good when cold, but requires 4-6 cranking attempts to start after it is driven and turned off for at least an hour or so. The idle is sometimes choppy and it has stalled once in traffic while idling. I have resoldered an open joint in the OVP relay that was causing the relay to be inoperative. The relay works now and I load tested it with a test light before reinstalling it. That seemed to help it run a bit better.

Meanwhile the fuel tank started leaking, so I have been fixing that. Once I had the fuel drained, I decided to check the fuel distributor and airflow sensor plate. I had previously noticed that the plate was too far down in the housing, so I adjusted it by tapping the pin up from the bottom until the plate came to rest where it is supposed to, according to the shop manual. I also checked the voltage on the airflow potentiometer, and it stayed low for the first bit of plate travel, then smoothly increased up to 11.7 v (didn't check battery) so it seems to be providing a good signal, I think.

The airflow meter plate still does not rise up high enough to strike the rubber stop above it. The shop manual says that the plate must "audibly strike the resilient stop" when it comes up. On mine, the stop is on a brass bar screwed down to the airflow housing. The bar has a bit of arch to it, and I am wondering if this bar is supposed to be flat, which would place the stop closer to the top of the airflow meter plate. Is this a big deal?

Also, I checked for evidence that the plunger seal was leaking and found that there was a good amount of staining from fuel, but since the fuel system was empty I did not pressurize the system and check for leakage. Is the plunger seal something worth worrying about?

Spark plugs are Bosch Platinum that came with the car, I plan to change them since the center electrodes look like they have receded, and I know they are bad for this car. But the appearance of the plugs seems to show a clean burn, no blackness or weird deposits. So I think the mixture is good, but will it need to readjusted after repositioning the plate?

I don't know how the mileage is, since the odometer is not working and we haven't really had the car long enough to fix everything.

[samiam4]

Two things..

First, if the flap is not coming up against it's stop- maybe you need to center it instead of playing with the height. That would be the first place to start.
Second, if you read any mercedes list, you will find the bosch plats are the WRONG PLUG for that engine. Period, end of discussion. Take them out and throw them away. Get ya a set of the standard Bosch copper core plugs. They are only about $1-2 each.
You could easily have a bunch of small problems.. temp sensor , air leaks etc. Then you'll probably have to adjust the airflow meter to undo it's current adjustment.

Michael

[bbarcher]

Yes the plugs will be changed. Thanks for your advice. I have centered the plate already, since it was binding if it was off-center at all. It moves freely and comes up to the prescribed height.

You reminded me that I also found the coolant temp sensor is reading the wrong resistance for temperature according to the shop manual chart. I tested it when cold and hot, and it has too much resistance, although the resistance does change with changes in temp. I used a digital thermometer with the tip placed at the cylinder head near the sensor and waited for the reading to stabilize, then I checked the sensor resistance. So there is a good chance the computer may be adding too much fuel for warm startup at times. But the car generally restarts fine as long as it doesn't sit for too long after driving it.

I wonder if anyone thinks it matters about the plate hitting the stop. I suppose it would cushion the return of the plate and prevent the plate arm from always hitting a hard stop and possibly being damaged over the long term.

[dkveuro]

The stop is a back-fire flap limit. Nothing to do with running.

The disc should be towards the top of the narrow part of the air flow neck at rest.

Bosch Super Plugs as per last post.

CTS ohms cold = 2500 ohms or more.
CTS ohms warm = 190 to 350 ohms.

Plunger leaking will cause hot start problems.
There should be no liquid fuel in the lower air flow meter plenum after 20 min's on a warm shut down.

.

[mctwin2kman]

If the Water Temp Sensor is bad then you will have hot start problems. Also the fuel accumulator by the pumps will cause hot start issues as well when it goes bad. I had the same problems and replacing that accumulator fixed them. Removing the return line from the accumulator when running and there should be no fuel flowing out of it, at least if I remember correctly that is the test. Search and you will find the test procedures on this site. This is where I got them from, mine tested fine but on replacement my hot start issues went away. I would first replace the Water Temp Sensor if it is reading wrong. The CIS-E Ecu uses that sensor to tell the EHA to adjust the mixture on the fly for proper mixture. Well that and the O2.... So that is pretty important for proper engine operation....