Bolomiester,
I've been watching your thread because of a very similar problem with my own car, a beautiful 1988 Triple Black 300SE. I just repaired this similar problem with duct tape. Try not to laugh too hard. This whole past weekend I was on this forum like a duck on a june bug, trying to make sense of all the years of experience these people have here. All the electronic lingo like ohms, potentiometer, cps ,ezl, cis, icv and such is pretty confusing.....But I'm hanging in there and will learn all this stuff. I consider myself pretty dang good at mechanics, and have been all my life, even as a kid. You have to remember and you probably are aware....In a gasser you need ( and this probably sounds pretty crude to the true pro's out there) gas, oxygen, and ignition, in the correct ratio for that all important combustion. Before you spend one more cent, and hours trying to figure out mutimeters and such (and maybe you've already checked, but didn't mention) CHECK the approx. one half inch vacuum line under the throttle body. It is a molded small length of hose, maybe 3" or so, that will split at the seems on both ends. I did not have a new hose, so had to actually repair the hose with duct tape. Put it all back together...She fired right up and is running great for 3 days now. The hose will split a little at first and as time goes by will get worse and so will your hard starts and stalling until the hose will allow too much air , there will be a backfire and that will blow the plum off the throttle body and the other thinga majig it attaches to. I hope some of you pros can tell me what that hose is called so I can order a new one. This all might not make a hoot toya or pertainto your problem, BUT maybe it WILL. Sure was a cheap fix. Maybe it will help someone out there............Good Luck

Wow, this actually makes sense! When I first bought the car it started and idled perfectly. It was only after a couple of weeks that it started doing its start/stall/start/stall thing, and it got steadily worst as time has gone by. As you saw, I replaced a lot of parts without success. It wasn't until I enriched the EHA by turning the adjust screw 1/2 turn CW that I got any improvement. It's not perfect, but much better. Kinda makes sense that if the hose you point out is leaking too much air adding a little more fuel would make things better. I'll look for the hose this morning. I replaced quite a few brittle/cracked hoses already, so one more makes a lot of sense.

Oh yeah, that hose (and the other old original molded hoses) caused me plenty of grief on mine. I shoulda mentioned that! One of them is tucked under the fuel rails in such a way that you pretty much have to open all the fuel lines and pull the distributor/airflap assembly out of the way to get to it. Then you find out that the replacement part doesn't quite fit the way it should.

Frustrating, but will make the car run much better if you address it.

Usually adjusting the EHA is just compensating for some other problem. You'll probably have to put it back where you had it if you have a vacuum leak that you wind up fixing.

The only molded hoses I see in the area are the ones for the ICV. I replaced both of them early in the game, and yes it was a royal pain. Is there another one that I'm not seeing?

I finally boned up on adjusting the duty cycle enough that I felt confident tackling it. I discovered the "no tamper" ball had already been removed so using the excellent instruction found here, I got the system in "adjust mode", and found my duty cycle hovering around 78%. I took a few tries to get it right, doesn't take much of a turn to make a big difference, but I now have it at 50% and the idle is VERY smooth, better than ever. In an hour or so I'll try starting it and we'll see what it does.

I wonder if a PO already fooled with the EHA and what I'm doing is putting it back to where it was before I got it.

I finally got the coolant temp sensor replaced. The first 22mm socket I bought wouldn't fit because of interference by the valve cover. I was tempted to loose it enough to make room but since it doesn't leak, I decided to try finding a thinner wall socket first. I took it back to Sears and learned something I didn't know. Wall thickness, at least on Craftsman brand, is thinner on sockets for smaller drives. I swapped the 1/2" drive socket a bought the first time for a 3/8" drive and it fit!

I think the car runs slightly better, (it's hard to tell since the car runs and idles very good already), but the start/stall is still there. The first start of the day is 2 trys. First time it fires instantly, revs to about 1,000 rpms then drops straight to zero and stalls. Second time it fires right up, revs to about a 1,000 rpms, drops to about 300, goes chug-chug a for a second or 2, revs back up to about 800 rpms then settles down to a smooth idle. If I then turn it off, it will restart perfectly with no sign of the start/stall thing. If I then let it sit for awhile, say 15 minutes or more, it will do the same thing it does on the first start of the day, though sometimes a little worst, maybe 3 or 4 trys before it settles down. But, again, if I turn it off then restart it, it's perfect.

I've replaced a ton of parts, but so far the only thing that seems to have made it better is turning the EHA adjustment 1/2 turn CW and resetting the duty cycle to 50%.

It just seems so odd that once it goes through its start/stall/chug-chug thing, it will restart perfectly until it stands for 15 minutes or more. I'm scratching my head to know what to look at next.

I was hoping to find a resolution in this thread. I have the same car as you with the same problem. Start,stall rough, stall, then runs fine. I just did a full tune up thinking that would help, not really.

Can you identify when your's started doing it? I'm surprised it has the same behavior with so many fewer miles. Mine has 191,000.

I bought the car in March and for the first 2 or 3 weeks it started perfectly without doing the start/stall/chug-chug thing. Then one day it took two hits to start, then it quickly got a lot worst. At the time I was in the process of tracking down and replacing age hardened hoses, but if I remember right the behavior just started out of the blue, not right after I replaced anything.

I just bought the car about a year ago. When I first got it, it would only do it some of the time. Recently, (last 3 months) it has gotten worse. I gave it a FULL tune up, with almost no difference. You can rule out any filters, as I have changed them all.

Thinking out loud, I want to say its a vacuum leak. My logic is when you start the car first thing in the am, no vacuum. It has to build up mabey? That would explain the easy starting after the fact. Im totally guessing, but it kinda fits.

I don't think it would be vacuum related. I'm pretty well convinced it's fuel related. Something in the fuel injection system somewhere. Like you I replaced everything ignition related.

I did one thing to the fuel injection that made things better and that was to adjust the EHA. I first went 1/4 turn CW then another 1/4 turn for a total of 1/2 turn CW. The car still does the start/stall/chug-chug thing, but as long as I start it with the AC off it always gets going on the second try. If I leave the AC it takes more trys to get it going. I also set the duty cycle after adjusting the EHA.

Once the car is going is runs and idles perfectly.

Sorry, I should have mentioned I got the 3/8" drive 22mm. I'm pretty sure mine is as well.

Anyway, have you checked the spec on the EHA instead of adjusting just here and there? I haven't done mine before but there is a specific value it should read when checked with a multimeter.

I took a 7/8 socket and hit it with a belt sander until it would fit between the valve cover and the sensor. Worked.

With the engine fully warmed up I measured the Ma by unplugging the EHA then jumpering from one pin on the EHA to one side of the plug, then from the other pin on The EHA to one lead on my meter and the other lead to the other side of the plug. Basically placing my meter in series with the EHA. At idle the reading is constantly jumping around from about -.65 to +.75. It never settles down to a steady reading. With the key on and the engine off it reads a steady 20.12. This test also turned on the CEL.

At the moment I have the EHA adjustment turned 1/2 turn CW (rich), which does make the car better than anything else I've tried.

Can you tell me what these readings indicate needs to be done?

"Archieves"

<<Once you have the amp meter and harness Part #10258904630007, you can remove the air filter housing to locate the eha which is located on the back side of the fuel distributor. It is a small black box with a two pole wire connector on it. Your harness will plug into the vehicles harness and the eha. There will still be a third connector this is were the amp meter leads go. Make sure the positive lead of your meter goes to the solid black wire on the test harness. Turn the ignition on engine off and you should have a reading of around 19 mili amps. If this reading is ok start the engine and let it warm up to operating temp. You should see the amp meter moving back and forth across 0 amps. 0 amps is your mid point so you should have even movement on the negative and positive side of 0. If you do not have this reading you will need to adjust the lamda. This is done buy moving the screw down inside of the lamda tower, which is located on the left side of the fuel distributor. I believe it takes a 3mm allen to adjust it. If there is a metal ball in place on the top of the tower you will need to get a new lambda tower and break the old one off. Install the new one and make your adjustments. The new tower will come with another steel ball its up to you if you want to reinstall it. Once you have the lamda set correctly at idle you need to bring the rpms up to 2500 and the lamda readings shouldnt change within 15% of your idle readings. If it does you have further problems. Also while your doing this make sure the eha isnt leaking fuel they prone to do this after some years and mileage. >

As you can see , they use a harness..but you do have the correct "In Series" connections..you can also do the same by simply moving the EHA over so it only plugs into one connector pin and then put the meter between the other exoosed pin and the empty socket on the connector..same deal, a series test meter hook up... just easier cuz you don't need jumpers.

Changed ECU
 

This morning, before starting the car for the first time of the day, I replaced the ECU with a used one. However, I then started it for the first time of the day and its behavior was the same as it has been as of late. At the first turn of the key the engined started right up, then the rpms dropped to zero and it stalled. On the second turn it started right up, the rpms dropped to about 300 then the engine chug-chugged for a second or two then settled down to normal cold idle of about 800 rpms.

Something I never really took note of before is that once it is started and goes through the second or two of low rpms and chug-chug, even though it hasn't warmed up, it will restart perfectly, rev to a little over 1,000 rpms, then settles down to a normal cold idle of about 800. I repeated this 10 times and it was always the same. A perfect start, no stall, no chug-chug, just a normal cold idle.

I'm letting it sit for a 1/2 hour and we'll see what its behavior is then, started, but not warmed up, then allowed to sit for a certain period.

After 45 minutes I started the car and it started normally on the try. No stall, no chug-chug. Then I turned it off and it restarted perfectly 5 time in row. Then I took it for a drive to get it fully warmed up. Turned it off and it restarted perfectly 5 times in a row.

Then I turned it off for an hour. After an hour the first try resulted in a rev to just over a 1,000 rpms, an instant drop to zero and a stall. On the second try it reved to just over a 1,000, dropped to 300, chug-chugged for a second then smoothed out a normal idle. ????????

Outside of this one fault the car starts, idles and runs like new.