Oscillating idle

pistrix · Jul 22nd, 2012, 07:54

Hi Everyone,

after a month of driving on LPG (1995 Volvo 850 20V - Prins) I still have a problem that when the engine is cold (but not immediately after it starts to run on LPG) the idle is very rough. It oscillates with about 1Hz below the normal idle RPM. I have no error codes and no warning lights. When running on petrol, idle is frozen still. I replaced the spark plugs, wires, distributor cap and rotor, cleaned the throttle body and idle control valve.

Any ideas what could be wrong?

btw, last time when they tuned the Prins system, they told me that the Lambda needs quite some time to "wake up" and starts responding with the proper oscillations...

Thanks,
Jan

classicswede · Jul 22nd, 2012, 21:00

Where are the manifold jets positioned in teh manifold?

pistrix · Jul 23rd, 2012, 14:01

Just by the petrol injectors (approximately 0.5 - 1.5 cm in the direction away from the engine)

pistrix · Jul 24th, 2012, 12:01

One thing I would like to add: These oscillations occur only when the engine is really cold like in the mornings. There are no oscillations during the day, even when the car is not running for 8 hours when I am at work and it still takes some time to switch from petrol to lpg...

Strange!

classicswede · Jul 24th, 2012, 19:14

If the lambda is slow to start working it is most likely due to the heater not working. The ECU does not start trimming the fuel untill the lambda has warmed up and working.

A common mistake Prins installers make is not T'ing the water connections in but putting the reducer in line. How are the water connections made?

pistrix · Jul 25th, 2012, 09:17

Quote:

Originally Posted by classicswede

If the lambda is slow to start working it is most likely due to the heater not working. The ECU does not start trimming the fuel untill the lambda has warmed up and working.

Do you think this might be the reason? Should I replace the lambda? Is the heater integrated in the lambda sensor?

Quote:

Originally Posted by classicswede

A common mistake Prins installers make is not T'ing the water connections in but putting the reducer in line. How are the water connections made?

I guess they used T parts to connect the water. Image: https://www.dropbox.com/s/75sa98y0b3sxg5s/IMG_0643.JPG Is this ok?

Thank you very much for your help!
Jan

Jul 22nd, 2012, 07:54	#1
pistrix New Member Last Online: Aug 5th, 2022 08:38 Join Date: May 2012 Location: Ljubljana	Oscillating idle Hi Everyone, after a month of driving on LPG (1995 Volvo 850 20V - Prins) I still have a problem that when the engine is cold (but not immediately after it starts to run on LPG) the idle is very rough. It oscillates with about 1Hz below the normal idle RPM. I have no error codes and no warning lights. When running on petrol, idle is frozen still. I replaced the spark plugs, wires, distributor cap and rotor, cleaned the throttle body and idle control valve. Any ideas what could be wrong? btw, last time when they tuned the Prins system, they told me that the Lambda needs quite some time to "wake up" and starts responding with the proper oscillations... Thanks, Jan

Jul 22nd, 2012, 21:00	#2
classicswede Trader Volvo in my veins Last Online: Today 20:09 Join Date: Dec 2004 Location: Anglesey	Where are the manifold jets positioned in teh manifold? __________________ http://www.classicswede.org www.classicswede.co.uk

Jul 23rd, 2012, 14:01	#3
pistrix New Member Last Online: Aug 5th, 2022 08:38 Join Date: May 2012 Location: Ljubljana	manifold jets Just by the petrol injectors (approximately 0.5 - 1.5 cm in the direction away from the engine)

Jul 24th, 2012, 12:01	#4
pistrix New Member Last Online: Aug 5th, 2022 08:38 Join Date: May 2012 Location: Ljubljana	very cold One thing I would like to add: These oscillations occur only when the engine is really cold like in the mornings. There are no oscillations during the day, even when the car is not running for 8 hours when I am at work and it still takes some time to switch from petrol to lpg... Strange!

Jul 24th, 2012, 19:14	#5
classicswede Trader Volvo in my veins Last Online: Today 20:09 Join Date: Dec 2004 Location: Anglesey	If the lambda is slow to start working it is most likely due to the heater not working. The ECU does not start trimming the fuel untill the lambda has warmed up and working. A common mistake Prins installers make is not T'ing the water connections in but putting the reducer in line. How are the water connections made? __________________ http://www.classicswede.org www.classicswede.co.uk

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