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Minimum unstable with cold engine


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I love my Lupo, but in a year it has had so many problems, certainly due to poor maintenance.
Yesterday another problem. With the engine cold, at the traffic lights, the idling started to be unstable, muttering quite a bit, until the car turned off. I try to restar the engine, fortunately it starts, I take a ride and I find an isolated place, at this point I accelerate several times very strong to see if it stabilizes. Everything looks okay, I do 10km and no other problem. The same joke had already done it two months ago, the mechanic told me that the throttle body electronics needs to realign and after a few km the defect disappears. I clean the throttle body by myself, which I did again yesterday. I get in panic because the car in May was totally blocked due to a fault with the G28 sensor. I have changed other sensors by myself.
Could the EGR valve be cleaned? Thanks and a have a nice day.

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Is it possible to measure your sensors with your diagnostics? They will tell you if the temperature is correct... if engine is hot, but sensor says only 30C (for example), then no fault found, but sensor is faulty :) You can do it with all the sensors.

 

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Hello mk2. The temperature shown in the dashboard is aligned to the VDCS diagnostic.

Now the trick I use is to pump up the gas a little and see if the minimun remain stable... Thanks for your suggestions.

 

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Google how a narrow band Oxygen (O2) sensor works, then it will help you find the fault. The voltage oscillates around lambda when the mixture is stoichiometric. Higher for rich mixture and lower for more O2. Around 0.45V average when perfect.

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  • 1 month later...
On 7/23/2019 at 10:27 AM, mk2 said:

Google how a narrow band Oxygen (O2) sensor works, then it will help you find the fault. The voltage oscillates around lambda when the mixture is stoichiometric. Higher for rich mixture and lower for more O2. Around 0.45V average when perfect.

Hi mk2, I didn't forget you... today I had the same problem but with hot engine, a kind of  "rattle" into the engine.

I  verified and no, errors, I raligned the throttle valve by vcds.

Can you tell me, please,  what is the "bank" to verifiy the lambda voltage?

BR

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  • 3 months later...
On 7/22/2019 at 11:13 PM, mk2 said:

Watch the lambda sensor voltage... it is a really good way of diagnosing fuel/air problems. In vcds, you can plot the voltage with time and temp.

Using USB scanner, I found "lean to rich sensor threshold" voltage max 300, current 865.

But I think that the real problem is the rubber pipe caming from EGR into the air filter, It brings oil and so push dirty stuff into the throttle valve.

What do you think about?

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Yes, i put a new pipe in place to divert oil breather fumes down to the road. Then no oil gets sucked into the engine. Also, you might want to remove and clean the throttle body. Then lubricate it well.

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