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1985 Maestro 1.6 automatic idle problem (S series engine)

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  • 1985 Maestro 1.6 automatic idle problem (S series engine)

    Hi, I have finally got my 1.6 automatic VDP on the road after a 15 year break and it appears to be running ok except the idle is fluctuating. Once the autochoke has switched off and the engine warm, it idles normally at 800rpm (or thereabouts) for about 10 seconds then rises to around 1200rpm for a few seconds and this cycle continues indefinitely. Now if I disconnect the vacuum pipe that runs from the Ignition Control Module to the autochoke switch then the idle is a little rougher but stays constant. So could the autochoke switch be faulty or the ICM or something completely different? The car tends to start on the 2nd attempt when cold, runs very rough for a few seconds then seems to be fine as the autochoke starts running properly and smoothly. I did think that maybe modern fuels might have damaged something (the fuel transducer was OK for example to start but now is giving wild readings) I have done around 150 miles in her since and also is feeling a little more sluggish now too under heavy acceleration. I'm a new paid member by the way, recently joined and very pleased with my early Maestro (33k since new).

  • #2
    Hi & welcome Calumb1, sorry for the late response.
    The idle speed cycling between 800 & 1200rpm is just a normal controlled response by the electronic idle speed control when the engine idle speed setting is set too low. You could just speed up the idle by turning the idle adjustment screw clockwise a full turn or however much it takes to noticeably raise the idle speed until the cycling stops. Then after waiting 30 seconds for the computer to return the stepper motor to idle position, you can very slowly turn the idle adjusting screw anticlockwise until the idle speed is 850rpm +/- 50rpm.

    But I would not start there because your starting from cold and sluggish acceleration point towards a possible problem with the ORFCO valve sticking open. To make sure the ORFCO valve is not stuck open, you need to remove the valve by undoing the three screws.

    When you look at the valve body (the bit where the gasket goes) there is a small oval hole at the end furthest from solenoid (the bit that the two wires connect to). Suck on that hole to see if you can get it to stick to your tongue.

    If you can suck air through then the valve is stuck open and you need to physically close it. To do that, unscrew the solenoid from the body and free the plunger with WD40 then refit the solenoid and recheck the hole is now sealed.

    Once you have refitted the valve do NOT reconnect it, as they are a constant source of unreliability. The best way is to just tape up the wires with insulation tape to make sure they cannot short out on the engine, and just forget about them.

    If the valve was stuck in the open position this will have a direct affect on the idle speed and CO setting. If the idle speed is still cycling carry out the procedure in the first part of this post.

    Cheers, G Force


    • #3
      Hi just to let you know that the car is now running very well and normally starts first time. I have replaced all vacuum hoses, the vacuum switch and orfco valve (with new ones, and yes the orfco valve was sticky in operation), temperature sensor & thermostat (also new and the thermostat was not closing properly). Biggest improvement was wiith replacing the 2 rubber tubes between the carb and vacuum switch which were shot to pieces. Idle cold or hot is now spot on and the car has powerful smooth performance. I found an excellent AR service bulletin on Youtube which went through all the major carb & engine management systems for the S series which showed both operating principles and fault finding and I found this very helpful too.
      Many thanks for your advice, now if I could only get more than 30mpg I would be delighted!


      • #4
        sounds good.... I've not had an automatic, but all of the 1600's I've had were pretty economical, are you driving in town or on open road?


        • #5
          Mostly on dual carriageways and motorways so I would have expected better, however my old Vauxhall Astra 1.6 auto never managed more than 32mpg (from tank fill to tank fill) so I guess it's not too bad. Possibly my driving style, I don't drive it too heavily but occasionally I put my foot to the floor.