Hello,

 

well its looks like my felicia has a little problem.

 

Its started Monday morning i start the car and the rpm are just to love between 550 and 700. I press the throttle but nothing happens. so I stop the engine and start it up, here again the rpm were to low, but it was possible to push it up to 1000 rpm. So I decided to drive at work, everything going fine.

 

After the work, I start up the car and, the engine goes up to 2000 rpm. I decided to drive and during the first 500m in the city, the engine was going up and down, from 2000rpm  to 900 the to 1500... 

So yesterday, I read a topic, where the temp. sensor could be the fault. Today I watched carefully my temp gauge and sometimes it was moving from ~80 degrees down to 0 and then up again. Maybe I should change it what's your opinions ?

You are noticing some issue with your temperature gauge, and assuming the engine management computer uses the same sensor as the gauge then that is an avenue worth pursuing. But, before replacing the sensor, check its functionality and check the signal and ground circuit-s.

 

One thing I'd like to know is if the RPM only goes crazy during idle, or also when you are applying throttle?

1 hour ago, LightRain said:

 

 

One thing I'd like to know is if the RPM only goes crazy during idle, or also when you are applying throttle?

Only during idle

OK, idle air controller could also be suspect. If the RPM misbehaviour immediately stops at the smallest application of throttle.

However, the temperature gauge jumping is the first thing I'd pursue. Does this car have a single sensor or one for gauge and engine computer? Does the idle improve after the engine has warmed up?

 

First I'd check the sensor's behaviour, unplug and measure resistance across the terminals when cold, then measure after running for a while, after a trip or something. The resistance should start off high and go low. Alternatively, remove the sensor and measure in air and in boiled water. I don't know the exact resistances, but someone around here will know and hopefully chime in.

9 hours ago, nimbus said:

Today I watched carefully my temp gauge and sometimes it was moving from ~80 degrees down to 0 and then up again.

Check simple things first. Start with corrosion in the connector of the coolant temp. sensor. Spray liberally WD40 in it. Then check the wires going to the connector by tugging lightly on them.

 

Of course all would be more efficient if you had a VAG-COM scanner.

OK I will check it later, before, I want to tell what was going on today by driving home, i needed to brake, and then the engine stops. I was trying to start it , arround2-3 minutes, finally the engine start and i could drive home. But :

-by pressing the clutch, the rpm goes up ( sometimes up to 4000).

- Sometimes by releasing the throttle, and applying again, it feels like the car brakes, and then it begin to accelerate.

- Sometimes the rpm is constant, without touching the throttle or going downhill.

And yes a VAG-COM scanner would be great

Edited 5 October, 20178 yr by nimbus

152 Ohms after driving home, this means around 85 Degrees.

How can I check the throttle body ?

A car of this age will be cable operated I think. So, if you want to check its range of opening get into a situation where you can see the butterfly and have someone slowly press the pedal and see if it  opens and closes smoothly and quickly.

 

This car (if the diagram I have is right) has only a throttle closed switch and idle air controller that are operated electronically. The switch is easy, it should be closed when the throttle is closed and open as soon as any movement happens to the butterfly, This can be checked by unplugging the switch and measuring resistance through the contacts. With the engine running there should be a voltage (probably 5 volt) on one of the switch pins (3 according to this diagram) and continuity from the other to ground (pin 4 I think). The IAC is a little trickier and its operation depends on its type, someone with more knowledge of this model would perhaps be better served in giving this information, but if you wish I can give you some general tips.

Its a simos 2p system with a Throttle valve positioner/ idle switch/potentiometer ( diagram from the haynes book ) with 5 wirings going to the ECU ( white, Black, Blue, Black/Yellow, Yellow.

 

And two other wiring comming from a knock sensor and the inlet air temp. sensor.

Now I feel foolish, I assumed it was an early model (you know what they say about assumptions).

Is this the diagram you are looking at?

I rarely trust Haynes diagrams, but assuming this is the right one then we can carry on.

 

As you are suffering idle issues, best to start with idle control and then throttle measurement. Using your multimeter, test the relevant pins for the below.

• Throttle closed switch, although this is probably OK as the issue stops when you apply throttle. With the ignition off. Resistance between pins 3 and 4 when the throttle is closed and when it is open. Closed should be very low ohms and open should be an open circuit. With the ignition on there should be fairly steady supply voltage going to pin 3, it is usually 5 volt. The other is a shared ground.
• Idle speed motor. Ignition off. Resistance between pins 1 and 2. It should be only a few ohms and certainly less than 500. With the ignition on and engine idling, both pins should show a changing voltage reading. If you had a scope you'd see a controlled on and off signal. 12 V max and 0 min, if your meter has the update speed to see that.

After those checks, next are the position sensors. 

Pins 6 and 4 are shared with both potentiometers. Test continuity between ground and pin 4. With the ignition on you should read 5 volt supply on pin 6.

These next tests require you to make a very slow sweep of the throttle from closed to open and back, the speed has to be very slow when using a multimeter because multimeters are slow to update.

• Ignition off. Resistance between pins 5 and 4 then resistance between 5 and 6. The resistances should change steadily as you increase throttle position, there should be no sudden changes. On slow release of the throttle the resistances should steadily go back to what they were before. With the ignition on, performing the same throttle sweeps, voltage at pin 5 should change smoothly.
• Ignition off. Resistance between pins 7 and 4 then resistance between 7 and 6. The resistances should change steadily as you increase throttle position, there should be no sudden changes. On slow release of the throttle the resistances should steadily go back to what they were before. With the ignition on, performing the same throttle sweeps, voltage at pin 7 should change smoothly.

That's about it. Of course, the problem may not be electrical at all, the throttle body could be dirty, it may not even be the throttle body at fault. These tests are quick and easy to perform (assuming good access) and give you positive assurance of the electrical state of the throttle body.

Hi, okay thanks for your knowledge.

 

Its exactly that diagram.

 

So i check between pin 3 and 4 but didn't have success, my multimeter pointers or to fat. So I decided to take a look to the MAP sensor (42 in the diagram and find corrosion on the pin c) i m pretty sure that should be the fault. I will try today or tomorrow to get and new sensor and connector.

 

Little question can I clean the throttle body with brake cleaner ?

Sorry for the bad quality of the pictures

That's the 5V supply to the MAP sensor. Maybe don't replace the sensor until trying to clean the contacts first? Maybe have a go at sanding or scraping them a little or cleaning with contact cleaner or alcohol. You can check the pin with your multimeter for 5 volts once cleaned and if it shows that you should be fine. You lose nothing trying to clean it up before replacing.

 

No problem using brake cleaner on the throttle body, carb cleaner would maybe be more aggressive if you can get it.

 

Could you send a picture of your multimeter probes? I have never seen any too fat to get into a component's connector

yeah good idea, I wash the connector and the pin of the sensor with wd40 and alcohol. the connector looks much better now, I tried to measure ( between pin C and chassis )5 v but nothing ( didn't starting the engine ) :/ maybe I need to let it dry, anyway finish for today, its dark and cold outside :P  

 

Edited 6 October, 20178 yr by nimbus

Ignition should be on when testing reference voltages, sorry I didn't say.

That looks much better than before.

 

They really are quite fat. A good investment for the future is a decent set of probes, the ones that allow you to attach a crocodile clip and piercing probe are really useful. Crocodile clip saves you having to hold onto all the probes all the time and piercing probe is great if you need to test a device while it is connected but can't backprobe it.

 

Anyway, good night.

Edited 6 October, 20178 yr by LightRain

9 minutes ago, LightRain said:

Ignition should be on when testing reference voltages

 

Just that I get it lol ignition on= engine on ??

 

When I say ignition on I mean engine not running.

ok ok thanks

@nimbus

You need to clean thoroughly both the throttle body and the MAP sensor, not just the connector. Cleaning the throttle body means removing it from the manifold. Don't forget to reset the throttle body after you finish cleaning it.

Edited 6 October, 20178 yr by RicardoM

Hi ,

 

So I don't have 5v coming out of the pin C.

Where can I find the connection point that is located at G-6 in the Haynes diagram ?

That supply is shared with the throttle body and the crankshaft position sensor. I'd measure one of their supply pins to isolate the location of the fault to the portion of wire from the splice to the MAP sensor. Just to be sure, key was on and engine was off and your other probe is to ground?

 

Locating that splice could be time consuming. Without the Skoda documentation you'd have to follow the wire until you find the splice. Look for where the sensors that share that supply join the larger wiring harness. This is a supply from the engine computer so it is likely downstream from the computer and up from where the last of those shared sensors joins the large harness. But, you may be able to estimate better when you're looking at the thing yourself. Also, someone with working experience on this car may know exactly where to look, maybe they'll answer.

1 hour ago, nimbus said:

Where can I find the connection point that is located at G-6 in the Haynes diagram ?

It is inside engine wiring harness. Not easy to access and to be fair you can follow LightRain's advice instead. If you cleaned the TB connector, the MAP sensor connector, the ECU connector and there are still issues, the best, quickest solution is to buy a VAG-COM scanner/interface/cable. Every DIYer that doesn't have money for a Skoda dealer garage should invest in one. Otherwise you're looking blindly for faults wasting a lot of time. Could be as simple as a dirty MAP sensor, dirty TB or more serious as a faulty MAP sensor or TB. From my experience Felicia is very reliable and the problems are corrosion or dirt related 99% of the time. It's an old car.

1 hour ago, LightRain said:

That supply is shared with the throttle body and the crankshaft position sensor. I'd measure one of their supply pins to isolate the location of the fault to the portion of wire from the splice to the MAP sensor. Just to be sure, key was on and engine was off and your other probe is to ground?

Yes

58 minutes ago, RicardoM said:

 If you cleaned the TB connector, the MAP sensor connector, the ECU connector and there are still issues, the best, quickest solution is to buy a VAG-COM scanner/interface/cable. Every DIYer that doesn't have money for a Skoda dealer garage should invest in one. Otherwise you're looking blindly for faults wasting a lot of time.

Maybe that what I should do, but does the felicia have  obd2 ?

 

 

I think that i will send the car to garage on Monday, I will give you feedback later in the week.

 

Thanks for help, its a really great community/forum

EOBD was required in Europe from, I think, 2001 (in the US OBD2 was required in 1996).

 

This car will probably have an OBD1 connector, the location, type and configuration of these vary depending on make, model and year. I don't know what you have, check under the steering, see if you have the EOBD mandated 16-pin socket. If not, it is likely an older type connector located in the engine bay or some other place, these usually require specialist equipment, although some can be read by monitoring for flashes on a test lamp and sending timed signals into the connector with a switch.

 

I don't blame you for not wanting to dig deeper in the harness. I recently spent 4 hours on an old Peugeot, balls deep in its motor harness just to find a tiny wire with a tiny bit of corrosion. Not fun, although being paid in beer helps .

 

Sorry I couldn't try and help you any further. Best of luck getting it sorted.