HDTech91

Hi,
I just recently purchased a 1991 190e 2.6 with 135,000mi on the odometer. When I bought it I was told it simply needed an alternatorand battery and it would be good to go. After getting it home and replacingboth I discovered that the car had many more problems. The issue that I amattempting to troubleshoot now is that the car will not idle. It will run if Ihold the throttle open and keep it above 1200rpm give or take but once it dropsbelow that, it will die. I downloaded a service manual and have been trouble shootingthe idle control system over the last couple weekends and have discovered thefollowing:

- The IAC valve physically works however; I am not receiving a 12v signal fromthe CIS-E module. The wiring for the IAC is Ok.

- The CTS and CTS wiring tested ok
- The Throttle valve position sensor and associated wiring tested OK
- The Idle/ full throttle switch and associated wiring tested Ok

According the literature I have, the air flow sensor is the only other inputdevice left in the idle circuit. I performed the KOEO test which was supped toyield 4.5- 5.5v at two of the sensor pins when the plate was manually pusheddown I saw less than 1v when I did this. Since it will barely run I will have ahard time performing the engine running test for the air flow sensor. I amthinking about picking up a used sensor and seeing if I get lucky since itfailed the KOEO test but I wanted to ask around and see if the air flow sensorson these engines were common failures to have. I am a heavy truck technician sotroubleshooting is nothing new to me but I am new to Mercedes. Any Ideas orinput would be helpful.

Thanks

vanir

I'm sure I'm just suggesting a backwards step you've already disqualified early on, but mine has done about the same miles and the spark plug leads are toast, the spark completely breaks down at low rpm and it's getting worse by the week (have to wait to budget the 200 or so for a new set, I've just spent a fortune).
I know I know, too obvious and simple to mention without sounding retarded but the way you specified battery and alternator got changed made me wonder if you checked the plug leads before getting too complicated, because at the same miles mine are dead and that causes idling problems.

Other than things like a leaky fuel distributor and thin timing chain on earlier engines these M103 are near bulletproof. Some have said it'll blow head gaskets but that's the M104. Our engine was so tough AMG decided they only needed to change bores and valves for their warmover and left most of the engine stock. Mercedes already had a lot of experience with the KE-Jetronic by the 80s so it's difficult to imagine any of the sensors in what Mercedes called the "over-engineered" 190E would be known as high maintenance or low lifetime. Never heard anything like that, but I have heard plenty these models keep soldiering on past half a million kms with relatively little upkeep.

On mine, at similar miles and very cheaply priced I might add, no service records or anything like that, all I had was a valve cover leak, had to get the fuel distributor reconditioned, and the plugs, the dizzy/rotor and leads were all toast. Leads I still have to replace.
And they're what's giving me idling/stalling problems. All the sensors/valves seem to be in pristine working condition. Like I said this wasn't exactly a concourse car, the dang thing wasn't even garaged in its life and I don't think owner's wifey ever opened the hood even once.
Fricken amazingly bulletproof car/engine as far as I'm concerned.

HDTech91

Thanks for the input, I had a similar thought but I checked for spark and I'm good all the way to the plug.

Over the last few weeks I have been working on it sporadically when I have had the time to do so. In reality, Ihave a far bigger problem than an idle shut down. After looking the engine over I found a multitude of vacuum leaks. I replaced all the damaged hoses and fixed all of the leaks, however, once I did this the car ceased to run at all. As I mentioned before, I pulled off one of the main vacuum hoses and the car would start and run if I kept it above 1200 rpm but it would not idle at all. Once I plugged the hose back in the car would not even attempt to start. I went ahead and replaced the air flow sensor with a used one that I sourced locally because the one on the car was physically damage when I bought it. I installed the new sensor but it did not solve the problem as I had hoped. I continued trouble shooting and found that the CIS module is not only failing to send any voltage to the IAC but is not sending any reference voltage to the potentiometer on the air flow sensor. I have tested the wiring for both and have no opens within the harness. I also noticed that I did not have a CEL bulb test when the key was on. I pulled the instrument cluster out and checked the bulb as well as voltage readings. The bulb was ok and I had no voltage to the CEL. I verified 12v to the CIS and Ground. In addition to this, I am not getting any fuel to the injectors. I know I have fuel up to the distributor and return out of the distributor but that is as far as it goes, no fuel is reaching the injector lines.
That may be as seperate issue completely but at this point I am leaning towards a faulty CIS module. I am not one to throw parts at a problem unnecessarily so any other ideas would be helpful.

Logon_Bob

Hey HD

mmm sounds like you have more than one issue but... Hard cold start and if it does start you can 't keep it running. #1 is the fuse on top of the OVP ( Over Voltage Protection relay ). It's in a hidden compartment behind the battery. It supply your 12v's to the ICV not the CIS. Also supplies power to the Fuel Pump Relay and the ABS system. Usuasly the ABS light comes on and stays on. No voltage to the CEL as well, maybe the ABS light is not working as well???

If the fuse is good the OVP could have failed. I guess you already know you have no 12v to the ICV key to run. Next would would have to get in the manual, there's a test for the OVP. Basically you pull the OVP and verify there's 12v's in the base socket but I don't recall which pins. If there is and no 12v out of the OVP it's bad. Some have been successful in re-flowing all the solder joints in the OVP.

IF just the ICV had failed, the engine will still run but too low cold and too high warm. This pulling a Vac line and it runs but attached it doesn't, strangest thing I have heard of. Sort of implies not enough air to run on idle. The ICV is normally open but if it stuck closed.... that might do it. Check the OVP first and fix that then the ICV.

Once you get 12v on key to the ICV,, oh, voltage will only be supplied on Key/run for 8-10 seconds, no engine running no signal to the ECU and it gets shut off.

Once you get 12v's and running, you can pull the ICV connector back just far enough to use a Multimeter on the pins but still connected,,, now you should see around 5-6 volts. The proper test is checking the current draw but this gets close.

ICV - pull the connector and Ohm across the 2 pins,, should be 12 ohms +-3 if not, it's bad and I don't think it can be fixed.

Next, the Air Flow sensor disc. It is very sensitive and must not bind. Simple test, break loose the main incoming fuel line on the Distro, watch your eyes as IF there is pressure... Now fully depress the Air Flow disc slowly feeling for any binding. Release and it should come up smoothly as well. Also clean it, no CARB cleaning spraying, could wash junk down into the ICV line. Spray the carb cleaner on a clean rag and wipe and wipe, depress and wipe some more.

Tighten the fuel line, key to run to get your 1 sec of fuel pump run and depress the air flow disc again, now you should feel a slight resistance but still no binding. Now you are pressing the fuel plunger. Resistance is slight but you can feel it.

You may be getting fuel at the distro but how much pressure? There are tests for the fuel pump relay but again, test the OVP first.

enough for now
Dan