Idle control valve query
 

Hi.. I've been having trouble getting my Rover 75, 1.8 petrol to tick over smoothly. It improves when I disconnect the rubber hose from the idle control valve to the front of the throttle body, in fact it drives more brightly too. Having taken off the valve to clean it I noticed that the piston in it was preventing air and after cleaning I could push the piston, albeit with some force, to an open position. Can anyone tell me how easy should the piston move? I have no idea what moves it so it would help to know if it is governed by a spring or perhaps a motor. Mine just seems stiff to operate..

The IACV is controlled by an electric motor (stepper motor) which adjusts the idle depending on the load on the engine, lights, aircon etc. The idle speed and datum point for the IACV has to be set using a T4 (maybe TOAF :shrug:).

Mike,
Have you fixed the low compression in cylinders 2 and 3 yet?

Yes there's no accurate way to set it up without T4 but if there's any loss of compression such as the valves not being lapped in properly then it's often impossible to get the adjustment down to what it should be ;)

It was on the service schedule but generally it was never carried out, it's essential especially if the throttle body or head gasket have been replaced.

Whenever I see a 1.8 it's almost always out of adjustment and I normally adjust it to spec if possible.

Russ

Most interesting as I'm due to visit a poorly 1.8T tomorrow and one of the jobs is adjusting the stepper motor. Is there a given value or will it automatically adjust once I get to ECM checks on the T4?

Regards

Go into engine management then into the maintenance menu you'll find all the stepper adjustments there.
It's not automatic, you can only make the adjustment when the engine temperature reaches 88°C it tells you which way to turn the throttle stop adjustment screw (remove the black anti tamper cap first ;)
You're looking to get it to 23 steps or there abouts, it's a case of timing when you press the continue button when the two black lines are within limits.
Don't worry if you mis-time it just try again until it's correct ;)

Make sure there's no additional load such as lights or Aircon whilst adjusting it as this will throw out the setting.
If you can't get it down to between 23-26 steps chances are there's lack of compression, usual suspect is the valves not being being lapped in when doing the head gasket ;)

Russ

Many thanks for the detailed description. Unfortunately the car is virtually a non-runner (will run on 3, but will not run on 4 irrespective of which cylinder is disabled) so getting it up to temperature will be a problem. We're getting an error on the stepper motor p1508, the wiring to the ECU has been checked). I'll try the procedure as we've little to lose at this stage. Same with the throttle position sensor P0122, wiring checked. Replacement ECU from K-maps. Comp. good, fuel at 4.2 bar.

Running out of ideas, and hopefully fault codes, and no-one can explain why it should run on three cylinders but not four, weird.

Keep well

As you did on mine when i had the Kmaps ECU fitted. :}

Crikey, you lost me at the word "Go"!

Hi Phil.. I'm not sure how you can fix a compression issue properly without taking the head off and checking the valve seals and seating so any pointers would be welcome. I have put in a Wynns oil additive to help but I'm not convinced that the 3 point difference would make much change to the tick over. It was fine before and it didn't run far at all when the gasket let go.. I got it towed home. The biggest difference is when I took the pipe from the idle control valve off and air was freely flowing into the throttle body. It increased the tick over speed a tad and was noticeably smoother at tick over and brighter to drive. You also noted a miss fire on one of the ht connections and maybe I should look there as well. It is frustrating not being able to adjust air flow and mixture... Having to wait for the ecu to learn any change.. Without a T4 to set anything is crazy for an old school Morgan owner like me.. Any thoughts would be welcome.. Thanks.. Mike