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SPI throttle position sensor, idle switch, engine temperature and lambda sensor
Published by andre79ge
05-11-2005
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SPI throttle position sensor, idle switch, engine temperature and lambda sensor

Hello!

I'm quite familiar with BOSCH mono jetronic fuel injection: I have a Uno 1.1 i.e. and I checked it from all sides and points of view in order to solve an idle problem.

However, I' try to describe to you some checks you can develop on your car in order understand something about your problem!!!

I'm going to describe some procedures for cheching your throttle position sensor (a linear variable resistor), your idle switch (a simple switch, the "plunger"), your engine temperature sensor and your lambda sensor.
All this is not so easy but neither difficult.

First of all: when engine is cold, ECU increases throttle aperture (in order to increase idle speed and let it run correctly).
So you can do the following thing:

1) With engine completely cold (for the first start in the morning after all the night, and BEFORE you turn on ignition key, watch the throttle pulley (it's the pulley that moves as you push accelerator; it is under the left side of air filter, if someone pushes accelerator, you can clearly see it to move and rotate).
You watch it and then let some friend to turn on ignition key and electricals (with or without start engine).
If idle switch and step motor (it is the motor which controls idle speed by changing throttle aperture) are good, you have to see the throttle pulley to turn automatically when your friend turns on the key. Infact ECU opens throttle a bit in order to permit to the engine to start and run properly at cold. This is a very simple and preliminar check. If nothing turns, probably you have a fault with one of that parts.

2) Then you can check your temp sensor: you have to identify your "intake mainfold"... Probably I can't translate it correctly in English, but it is an "one part" 4 tubes metal object which connects air/fuel/mixture intake to the head of the engine. So, see at your engine from the right side (opposite to throttle pulley) and point attenction to the distributor. Under the distributor there is that collector (you can see only a part of it because it's covered by air filter and other stuff). On the right side of this You will see also a "plunger" with a black cable which exit and goes out of hte engine zone: that is the engine temperature sensor with its wire connection. With engine cold and not running but ignition turned ON, you have to disconnect the cable (it's easy to do: you have to push the little metal object which locks the connection, then you have to pull the cable...here I have another translation problem because I can't explain and describe this procedure better). As soon as you disconnect, you have to see your throttle which closes air intake (in other words, you have to see throttle pulley to rotate and which returns in the position it was before you turned ON the ignition key during step 1).
Reconnect the cable and see the pulley to turn, opening air collector another time.

You also can start engine and try to connect/disconnect with engine cold and warm:
When engine cold, it have to work normally with the cable connect, and not to work correct with cable disconnect (because ECU have not the information of "engine cold" if you disconnect the sensor.
When engine warm, cable is not longer important (sensor is only to note that engine is cold; if engine is hot, ecu doesn't need any information about temperature) and engine have to work with or without its connection. IF engine runs better WITHOUT that connection, then you have the sensor faulty and probably you have solved your problem. But I think this is not your problem.

3) Lambda check.
This is a little more complicated because you need a tester (at least). Tester is not the best you can use: I have a little electronical circuit which permits to test lambda (ald also all the fuel injection system) very precisely. It's an easy circuit (only a chip which produces all you need all by itself, and a series of 8 led in order to see the output). I can describe it if you have some confident with electronical stuff.
However, if you have a tester you can roughly check your lambda.
Let me know if you are able and interested in this measure and I'll try to explain it!!!

Very very sorry for my English, but I'm Italian and I studied English only at school... then I have a lot of difficulties to understand what you wrote and also I'm not used to write...
I hope to be helpful! Let me know for all you need and I'll try to help you.
That are basic test you can perform on your fuel injection system.
If you perform that checks in this way, you will not cause problem to your electronicals or at your engine, don't worry!!!
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Old 17-10-2006   #1
Join Date: Sep 2006
Location: Southport
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Re: SPI throttle position sensor, idle switch, engine temperature and lambda sensor

HI, I have a Bravo 1.4 SX. It has a Lambda sensor. Can you explain to me how to check the sensor with a test meter ( multi meter ? ).

Regards

SC
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mercanlandy is offline Reply With Quote Quote 
Old 02-08-2007   #2
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Re: SPI throttle position sensor, idle switch, engine temperature and lambda sensor

can you reccomend where I may purchase the above for a 2ltr petrol posting in the UK.......looking forward to hearing from you
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