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  #1  
Old 01-05-2005, 09:35 PM
djimmy31
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Throttle Microswitch

Hey guys,

What does the throttle microswitch do and what are the symtoms when it is bad? I was advised that mine was bad and needs replacing. The car is running like crapola.

Thanks

Jimmy
1988 Benz 300e
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  #2  
Old 01-06-2005, 03:37 AM
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Join Date: Jul 2004
Location: Sydney, Australia
Posts: 197
The microswitch is just there to provide an idle throttle position signal for idle control and fuel shutoff on decel.

This won't give an effect of a general rough engine running. What are your symptoms?

A simple check of the switch is to check for an open/closed circuit when the switch is open/closed.
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Alex.

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Volvo 122S
W201 190D 2.5 manual
W202 C240
W203 C32
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  #3  
Old 01-06-2005, 08:37 AM
djimmy31
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Hey AusMBtech,

Hmmm... When I give the car gas sometimes it will go just fine other times it will stumble, spit and sputter. If you feather the throttle it sometimes will do fine but take off normaly and you get the spit and sputter. If you floor it it will try and die.
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  #4  
Old 01-07-2005, 05:50 AM
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Join Date: Jul 2004
Location: Sydney, Australia
Posts: 197
Just sticking to fuel delivery faults it sounds like it's running lean on acceleration.

High control pressure, EHA not working, general lean running, carboned up valves (yep, it'll do it) can all cause these problems.

If you have terminal 3 in your diagnositic connector then check your lambda value first. 50% is normal for most engines but the 103 engine (which I presume you have) prefers to run at 30-40% (I put it on 35% during services), they run quite well at this mixture, 50% is too lean on acceleration from experience. You can check you EHA (if fitted) for operation by watching the lambda value fluctuate +-5%.

A can of carby cleaner down the intake on a hot engine will also help if you haven't done it in a while. Make sure you do it on a hot engine and try and keep the lowest rpms possible without stalling (to help saturate the carbon and make it break off the valves).

Give those 2 remedys a go since they are simple and don't require much in the way of tools.
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Alex.

MB Tech
Sydney, Australia
Volvo 122S
W201 190D 2.5 manual
W202 C240
W203 C32
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  #5  
Old 01-08-2005, 12:06 AM
djimmy31
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I will give those a shot this weekend and see what happens. Thanks for the advice. Hopefully it fixes as I am getting gray hair messing with this thing
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  #6  
Old 01-09-2005, 12:55 AM
djimmy31
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Hey AusMBtech,

I was messing with the #3 pin on the x11 do I need to unplug the purge line when testing? If so where is it at? Here is where I got that from http://www.landiss.com/mixture.htm

I should have some #'s tomorrow.

Thanks for all the help. Hopefully I can have this thing back on the road here soon.
Thanks

Jimmy
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  #7  
Old 01-09-2005, 01:21 AM
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Yes, you will need to block/disconnect the purge line while checking mixtures. There should be a valve on the LHS/intake side of the engine bay with a few hoses going to it. It may have a "purge" marking on it. I'm sure someone on this board could provide a picture of it.
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Alex.

MB Tech
Sydney, Australia
Volvo 122S
W201 190D 2.5 manual
W202 C240
W203 C32
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  #8  
Old 01-09-2005, 11:19 AM
djimmy31
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Okay I am still trying to find the Purge Line but I went ahead a did some test not sure if the are worth anything or not.
Car idles great during this whole time.

KOEO
1. pin3 and pin2 =70%
2. pin3 and pin2 =10% (deflect air flow sensor plate)
3. pin3 and pin2 =20% (open throttle completely)

Could not find purge line to unplug so these test may not mean anything!!!

Engine on
1. Pin3 and Pin2 =49.7 (#'s did not move, car was just started)

After car warmed up the #'s get weird. Numbers started to change around 60 celcius.
They start at 45%flucuate down like this
45% 43.5% 42.7% 40.9% and it does this all the way down to 7% where it stays steady. If at anytime I hit the throttle it sputters and spits and then returns to around 50% and it starts going back down again. ( if you reverse the black and red between pin 2 and 3 it just reverses the % so it could be going up to 93%) Either way hitting the throttle it spits and sputters and then returns to right at 50% and starts counting back down to around 7%.

Again this may mean nothing since I didn't unplug the purge line.
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  #9  
Old 01-09-2005, 04:06 PM
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Join Date: Jul 2004
Location: Sydney, Australia
Posts: 197
Try disconnecting the EHA and go for a drive. You may have a bad O2 sensor which is sending the fuel mix too rich (low %). I've got the list of fault codes (each value in 10% increments means something when engine not running) in my toolbox so I'll reply with those in 12hrs
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MB Tech
Sydney, Australia
Volvo 122S
W201 190D 2.5 manual
W202 C240
W203 C32
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  #10  
Old 01-09-2005, 11:38 PM
djimmy31
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Hey,

I unplugged the EHA and let the car warm up. Took it for a drive and it seemed to make the problem worse. A friend of mine seems to think the coil could be bad. We took a look at the spark and he didn't think it was that strong. I guess I could replace the coil.

Also we looked at the old plugs and they seemed to have a little a carbon/sooty look. I guess that would be to rich.

One more thing with the EHA unplugged I looked at the duty cycle and it was sitting right 7.3%. That seems to be way way to rich. If I hit the throttle though it goes back to 50% and then counts down to the 7%

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  #11  
Old 01-10-2005, 03:14 AM
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Location: Sydney, Australia
Posts: 197
Ok, I checked the fault codes and the figures to gave me show that all is ok with the switches (10%, 20% and 70%).

Run the engine till hot then shut it down. Press the air flow plate down and smell inside. If there is a strong smell of fuel then the seal at the bottom of the fuel distributor may be leaking fuel into the manifold (explaining the excessively rich mixture at idle)

Otherwise I'd just try leaning out the mixture a quarter turn at a time (remember how many turns you do) until you get it back between 30-50% at hot idle and 50% at 2500rpm.

Was this problem sudden or has it slowly been getting worse?
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Alex.

MB Tech
Sydney, Australia
Volvo 122S
W201 190D 2.5 manual
W202 C240
W203 C32
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  #12  
Old 01-10-2005, 08:57 AM
djimmy31
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Lightbulb

I will try that and see what happens.

The problem was sudden. The morning it happend it dropped down to freezing weather and thats when it happened.
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  #13  
Old 01-10-2005, 09:53 PM
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Location: Near Raleigh, NC
Posts: 580
I do not think the purge line makes much of a difference at this point.
You are getting a fixed reading of 7% when the engine is warm. A fixed reading is a fault code. The manual does not have a fault at 7%, but the closest one is 10% (air flow position sensor / potentiometer).
It appears the potentiometer is worn at the idle position.
See if you can rig long wires into the cabin with the meter connected, monitor the duty cycle while driving and see if it sticks to any fixed value.
If it just keeps oscillating you do not need to adjust your mixture, mixture is OK. If it sticks to any value, then you have a fault.
The pots are known to wear right at the idle position, hence rough idle and fixed duty cycles at 10% (warm and idling engine).
10% is also a code for faulty throttle valve switch.

My 2 cents.
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  #14  
Old 01-12-2005, 08:33 AM
djimmy31
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Hey,

I tried leaning the mixture out and it did work accept for it would return to 7.6% and stay steady right there. If I hit the throttle a couple times it would return to at that time 58% (from leaning it out) and then count down back to 7.6% I guess I will try and replace the air flow position sensor / potentiometer. Thats the sensor on the side of the air flow housing right? Also what is a throttle valve switch? I couldn't find that on a parts site anywhere? One last question where can I buy just the potentiometer, I don't want to buy the whole housing?

Thanks

Jimmy

ps is these 2 parts don't fix the car it's going up for sale. It's driving me nuts.
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