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Hard starting and stalling on decelleration; plus an introduction
Topic Started: Fri May 28, 2010 2:30 pm (1,065 Views)
zhenya
Newbie
[ * ]
First, I should introduce myself. I'm the new owner of a 1987 US-spec 190e 2.3-16. I realize this forum is UK-centric, but the knowledge I've found in your archives has been fantastic, so I'd like to get some of your input on some problems I'm having with my car.

Since before I bought the car (the seller warned me about it), the car has started very hard when hot. You have to floor the gas pedal while cranking, at which point it usually catches. It takes work to keep it running at this point - but typically 5-10 seconds on, it runs ok. It typically starts quickly when cold. (more on this later, though).

The second, even more worrying problem is that sometimes, when I push the clutch in to come to a stop or to take a turn, if I don't downshift, the car will stall. Watching the tach, the revs will drop to about 500, at which point it will typically catch and be ok. Sometimes the oil pressure drops at this point from 3 to about 2. Usually it does not stall at this point, but it can be dangerous when it does.

I have been going through the system as well as I can for never having owned a non-EFI car before.
-I have checked the OVP fuse
-Fuel pump works and I think the relay is ok - but not 100% sure
-I have tested my fuel accumulator and believe it to be ok
-I have tested the ICV by connecting it to 9v and proving that it fires
-I have tested the Throttle Position Switch and believe it to be ok
-I have tested the air meter potentiometer, and believe it to be ok, but I am not 100% certain.

At this point, I am leaning towards the airflow sensor plate height. However, since I have never worked on or seen this part before, I would like to be 100% certain before I start to fool with this part. The reasons I am leaning towards this plate being the issue are that:
- There is no free play in the plate. It appears that at its resting height, it is already resting against the metering plunger. My understanding is that it should have 1-2mm free play before making contact.
- If I am looking at this correctly, I believe its resting position is a bit too low. I am looking at the position relative to the machined cylindrical surface on the right-hand side of the car, under the support bar (as viewed from the front of the car facing the rear).
- With the car idling, it often just barely holds an idle, even though the rpm's are at about 950. If I put even the slightest downward pressure on this plate, the car stalls and dies.

I would sure appreciate any input anyone can give, because as much as I love this car, this problem has to get sorted - it's no fun driving it when I am constantly worried about it stalling. Thanks!
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G3MAW
Part of things
[ *  * ]
Hi Zhenya,
You appear to have done all the right things - running faults can be tedious to sort out. Sounds like a classic case of running a weak mixture ( engine dying on hot idle). A couple of suggestions :
Check the engine air hose circuit for leaks, especially the main hose which connects to the underside of the air flow metering chamber and the connections to this hose around the ICV, the primary pressure valve ( mounted adjacent to the Air Flow meter ).
The Air Flow metering chamber itself is made out of rubber, which perishes with age and can leak air.
Check for an air leak in the engine idle speed adjustment ( underneath the air box and accessible with a screwdriver from the left side of the rocker cover, looking at the windscreen). Any lack of tightness on the adjusting screw might indicate that the rubber seal has worn down and is leaking air, so upsetting the idling.
Check the ignition distributor vacuum capsule, mounted on the side of the unit for an air leak ( disconnect the hose and test for leaks by sucking air from the capsule through a clean piece of tubing. If this is OK you should hear the movement of the advance plate inside the distributor with no air leaks).
If all of the above are OK, then I would suspect the fuel pressure system ( weak mixture = too much air OR low fuel pressure). The pressure can easily be tested by a competent mechanic with a meter ( use the cold start valve connection on the fuel distributor). Warm up the engine and watch how long the fuel pressure is maintained after you switch the engine off - it should stay at around 40psi for at least twenty minutes. If it doesn't then you need to inspect the fuel injectors ( a bad one will leak fuel when the engine is turned off, leak away fuel pressure and so you are forced to start churning the engine to restore fuel pressure before you can re-start). Another clue, here, is a strong smell of fuel after you switch the engine off.
Sorry to go on - like I said, it can get tedious, but do one thing at a time and you stand a good chance of eliminating the fault. Good luck!
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GEZIJ
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Part of things
[ *  * ]
Hi there and welcome, i had the problem with stalling when dipping the clutch, it turned out to be the Idle control valve (ICV) . I found that periodicaly spraying wd40 into it would keep it working for a while until i sourced a new one.
have a look to see if there is an adjustment knob on your ICV, you can turn it may idle better at 10000 rpm.
As for the starting issue when hot, i havent had this problem so cant offer any guidence there im afraid. but im sure someone here will know something.
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zhenya
Newbie
[ * ]
Thanks guys. Before I tackle anything else, possibly bigger, I've purchased a meter today that will do duty cycle so I can check my mixture, to try and determine if that is off.

I've tried following the guides here - http://mercedes-190.co.uk/topic/6620540/1/#new - but I'm not seeing what is expected.

With my car off, ignition on, I read 50.6%. Car on, idling, but cold, 50.6%. Once the car comes up to temp, it goes way up to 95%. If I give it some throttle, it drops to 45%, (let me re-state that) - when I hold the throttle, it stays at 95%, when I let it go, it momentarily drops to 45%, then it slowly goes back up to 95%. Adjusting the mixture screw does not seem to change this 95% reading.

I'm not sure what all this means??
Edited by zhenya, Sat May 29, 2010 3:23 pm.
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zhenya
Newbie
[ * ]
Ok, another test - trying to verify the function of my oxygen sensor now. I plugged my meter in to the cylindrical plug under the seat as per http://mercedes-190.co.uk/topic/223164/1/#new and started the car. Car was already warm, and when first starting the meter measured 0.48v. I gave it some gas, and the reading slowly climbed to 0.78v, where it seemed to stay steady as long as the car was at idle. As I gave it gas, the reading drops in a linear fashion, say down to 0.7v at ~2800 rpm. I think this indicates that it is functioning, but perhaps running very rich?
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balamb37
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Grumpy Old Grampa with Dog
[ *  *  *  *  *  * ]
I don't think it would be an air leak causing a weak mixture as that would increase

your idling revs above 1000 RPM.

I would be looking at the fuel delivery side of things starting with the filter and delivery pressure

as mentioned by someone above.- ( Injectors, ICV etc.).

The mixture screw I would steer clear of as if you upset that it can be a barst*** to

'get it all together again' without the correct gear.

After all it is set in the factory and won't move on its own accord,

unless a previous owner has been playing with it ;)

But as G3ZIJ says take one thing at a time otherwise you could end up with several faults.

Good Luck and welcome.
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zhenya
Newbie
[ * ]
balamb37
Sat May 29, 2010 4:41 pm

The mixture screw I would steer clear of as if you upset that it can be a barst*** to

'get it all together again' without the correct gear.

After all it is set in the factory and won't move on its own accord,

unless a previous owner has been playing with it ;)

Yes, I know that the previous owner played with the mixture screw, because he showed me how it was done - except that I don't think he ever used a meter to check actual values! I'd like to get that sorted before I move on to other steps, as this seems to be the basic starting point. Any comments on what I'm seeing from the x11 connector on duty cycle? Or about my oxygen sensor test?
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zhenya
Newbie
[ * ]
Ok, here is where I am at after a full day of working on this. I continue to get very erratic readings from the meter regarding my mixture. I cannot tell if I have a faulty o2 sensor of if my idle mixture is just so far off that the meter is giving me odd readings. I purchased a new o2 sensor, but unfortunately was unable to budge the existing one - I soaked it in penetrating fluid and heated it, but the split wrench was beginning to open from the torque. I may have to take it to a garage to get it out.

Anyhow, one thing is clear - the car is is excessively rich at idle. It smells, and after idling it in the same spot for a long time yesterday, I have a huge black spot on the concrete.

This is interesting though; when I pull the idle air valve hose that goes in to the valve cover, obviously the idle rises to about 2400, but also, the black exhaust goes away and at that point, I begin to read 45-50% duty cycle. I mentioned above that I had tested the idle air control valve before, and seen that it does trigger when given 9v (used a standard battery, which provides enough voltage). I notice that the normal rest position for that valve is about 1/4 open. Does that sound correct?
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GEZIJ
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Part of things
[ *  * ]
yer, icv sounds like its working.
if the mixture screw has been tampered with i would suggest taking it to a Bosch service centre to have it reset.
a fine adjustment of that screw can make a hell of a difrence.
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balamb37
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Grumpy Old Grampa with Dog
[ *  *  *  *  *  * ]
+1
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zhenya
Newbie
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ok, sounds like a good plan guys. now I just have to find someone who remembers how to work on KE-Jetronic...
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