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Discussion Starter #1
Hello!

I have 156 1.8 TS 1998 and a week ago when I wanted to change the radiator it started to act weird, the most annoying was the rough idle, from 500 to 1500 rpm. Changed the radiator, everything went fine but still rough idle. The same thing happened when I swapped the engine and a friend told me that it is MAF and I changed it and everything was great!
Tried: changing the MAF, diagnostic-no errors, cleaned the throttle body, made patches on air inlet after the MAF, checked for air leaks on inlet manifold and air inlet-NOTHING MADE THE SITUATION BETTER. The only thing that I have found was that when the car is idling (rough) the lambda sensor sends a 459 mV signal and it isn't changing, it stuck there even when I put my foot on accelerator. MAF is sending the signal od 1,5 to 1,7 volts, depending on the accelerator position. When I try to drive it, my exhaust is busted after the lambda so I hear terrible noise when accelerating, small explosions and the acceleration is not so good. Maybe something will happen after welding the exhaust but I wouldn't put my money it.

I know that there is a bunch of same issues and topics on the forum but I tried to find a solution, googled it, searched the forum, nothing helped...I don't have an Alfa specialist so it is up to me and my cousin (car mechanic) to find the solve the problem.

Thank you!
 

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Your car has just the one lambda I think? In that case the output voltage should be cycling up and down fairly quickly at idle, something in the range of 0.2 - 0.9v.
 

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The engine management would ignore the lambda (open loop control) until the engine is up to operating temperature (closed loop). How long this takes would depend on a few things!

But 0.459V is around the "perfect" air:fuel ratio (i.e. 14.7:1), so this may just mean the management system is running is open loop and therefore reporting a default value. Or it could indicate a fault with the sensor..

Can you get a reading of the voltage when the engine is warmed up?
 

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It should be cycling point blank. Sounds like the sensors bust if it doesn't.

The lack of back pressure from a broken exhaust will only make things worse.
 

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Discussion Starter #6
Tested the voltage when it is on 90 celsius but it is the same, stuck on 0.459. lambda is very close to the exhaust flex part so this was my first guess that is messing up data from the lambda but everyone said that this shouldn't make any difference. I will try to take off the lambda and clean it and test it with heat with multimeter. Thanks for the advices!
 

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Just get another one... it shouldn't have a flat signal.
 

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Sounds like there's a fault in the sensor alright, maybe a break in the circuit somewhere.

Worth checking the loom where the sensor plugs in to make sure the wiring there is ok..

Otherwise, unless you're able to take these sort of things apart I agree it looks like time for a new sensor, unfortunately.
 

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Discussion Starter #9
My car is at exhaust mechanic, should be done tomorrow so crossing my fingers that all this is because of the exhaust because I searched the net for problems with lambda and there is a bunch of them saying that even the rear exhaust if it is broken could mess up the data of lambda. So lambda is close to flex part of the exhaust...maybe the there is a loss of pressure on lambda as someone mentioned. Will report back! Thanks!
 
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