Hello Everyone: I am very grateful for the ability to join this forum. I have a 1991 300e, have 118k, that has allot of difficulty starting cold or hot.

This problem started when I jumped terminal 85 to 30 on the block that the relay behind the ovp relay sits (now believe this relay is connected to the cruise control) I thought that this might be the fuel relay but later confirmed that the fuel relay is build into the MAS unit. The fuse on the ovp blew and I have had starting problems ever since beyond my initial issue (popping in the intake manifold, which I have experienced before and was resolved with new injectors). This time new injectors did not correct the problem. So, I opted to change the fuel distributor since they are notorious for problems when left the car is sitting for extended periods with little to no use. My fuel pressures are within limits. I have replaced the fuel injectors, the fuel distributor. A few months ago, I changed the fuel filters and both fuel pumps. To try to resolve the low idle issue, I replaced the temp sensor and the OVP relay, installed a used but "tested good" CIS-e unit and MAS unit with no change, installed a new fuel sensor (potentiometer) and it is set to the required .70 volts at idle. My car will start if I step on the gas but it will die out. If I allow it to crank for about 20-30 seconds, it will finally idle but very low idle. It runs like this for about 2 minutes and then seems to go to limp mode. My eha current with koeo, is about 12 ma ( think it is supposed to be 20 ma), it rise to about 30 ma while cranking and then falls to about 1-2 ma at low idle at normal (hot) engine temp. When the car goes into what I think is limp mode, the idle increases to about 750-900 rpm. My duty cycle fluctuates between 49 to 42 %. The eha current is at 0-2 mA. Periodically, the idle will rise to about 950 rpms and my duty cycle changes to about 30-39%. Snapping the throttle brings it back down. I have checked the continuity and resistance to all of the following circuits and sensors: the eha, the icv (gets 11 volts on pin 2 and about 750 ma until limp mode then voltage drops to 4 volts- should there be voltage on pin1?) the temp sensor voltage is 5 volts and resistance of the new sensor is within factory limits, the micro switch has normal resistance and is working to open the circuit when off idle. The throttle valve switch is working as designed. There is no increase in eha current upon raising the idle I think that is because cis-e unit is in limp mode). All continuity checks to and from the cis-e to the temp sensor, the icv, the eha, the cold start valve wiring pass ohm tests. Not sure what is causing it to go into limp mode. I do not own a pulse reader. The x11 on off ratio fluctuates and periodically holds 49.9 percent for 1-3 seconds and then fluctuates. I thought that perhaps the fuel sensor was the problem. I replaced it and it checks out fine. While in limp mode should I still be able to see lambda results? Any help will be appreciated. In case, I didn't say it, I got a used cis-e unit and MAS unit incase I may have shorted one or both of them with my initial attempts to jump relay to put fuel pumps on with key off to check fuel pressures. I hope that someone is able to understand my thread and help me figure this out. Beginning to wonder if the "test good" used cis-e unit is bad. I get the same problems if I reinstall original equipment.

Hello again:

I bought a new meter that can read the eha amperage. I do have 19.80 Ma with koeo. When I am cranking the the eha current drops to about .59ma, then when it starts the amperage is .01 mA. The idle is about 300 rpms. It will stay that way for about 2 mins. Then something changes. The idle increase to about 700. Then I noticed that the eha amperage will gradually start to climb and continue up to 5.5 mA, raising the idle to about 800-850. Then the eha will drop suddenly to less than 1 mA and then it will start this process all over. It is like a cycle of the eha current going up and then down and the idle moving with it. The eha current is increasing momentarily upon sudden acceleration sometimes as higher as 40 mA depending on how hard I step into the gas pedal but quickly drops the current to about almost 0 mA. This seems to be erratic when it does it. Sometimes, it will pop in the intake manifold. It seems like this happens when the current on the eha is low.

Thank you for taking the time to read my thread. I appreciate any assistance I can get to figure this out.

Tim

I went back out to the car to watch the eha current at idle. It fluctuates between 0.20mA to 1.69 Ma. If I step on the gas the eha current doesn't increase right away. If I hold step on the gas to really raise the rpms, it hesitates and the eha current drops initially. Then, it starts a very slow rise. As the eha current rises, the rpms will rise and smooth out. For whatever reason, it seems the eha current drops and then slowly rises. Other times, it will rise to 2ma ands then drop to 0.020 mA. The response seems pretty erratic. Not sure what I can check. I'm wondering if the ecu is junk and displaying such odd responses. Anyone with any thoughts is appreciated.

It's possible the EHA or ECU is bad or both. I have gone through 2 EHA's on my car in as many years. One had internal electrical problem, one had leak. The ECU's are also just as susceptible as any other electrical box to failure. I had an ECU fail in my car, it ran OK, but it never went into closed loop.

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1991 300E - 212K and rising fast...

thank you for the reply... I was hoping for more technical information, perhaps from some of the big guns on this forum, that could help me narrow the field.

I haven't received alot of help from the furom but I wanted to share what I discovered. The terminal number 85 is the ground for the relay that sits behind the OVP. The terminal 30 is battery current at all times. So, when I jumped the two points, I blew the fuse on the OVP and have been chasing a low idle start ever since. I'm not sure if this is coincidental or I shorted something in the idle control valve but I replaced it. Now, my car starts hot and cold, with fuel enrichment and initial idle increase as expected, gradually settling down to about 700 rpm. With the new meter, I'm getting reliable readings of the eha valve current. It is 19.80 mA at KOEO and about 10 mA while cranking when cold. This amperage quickly and gradually drops as the engine temp increases and the dile continues to fall toward 700 rpm. At 80 degrees C, the eha current is adjusted to fluctuate between -00.40 and 00.60, I prefer it to be slightly rich. I'm still experiencing a pop in the intake and I notice that the current to the eha upon acceleration does not reliably increase, especially if I step quickly on the pedal to quickly raise the rpm. Gradually increasing the idle is less problematic. I'm going to check my fuel pressures again to confirm that they are within the acceptable range. It is a new fuel distributor and new fuel injectors. Hopefully, these are fine. I put on a new fuel sensor and it has about .7 volts at idle and the voltages on pin the top and middle pin are what factory specs require and increase to almost 5 volts as I move the air flap. When I check the resistance on these two pins, the resistance changes but there is a point when it goes to infinity for a second and then the resistance comes back. This is notices especailly with sudden movements of the air flap. Can this be the reason for the occasional pop in the intake when sudden acceleration. Finally, I noticed that the fuel regulator does not hold vaccum on the vacuum connector designed to sliughtly increase fuel pressure when vacuum is high, like sudden steps on the gas. Any help would be appreciated. I'm making progress.