High idle speed on 460 SE 2.0i

[Shady]

I seem to have lost myself in the Haynes manual. My idle speed is quite often staying at 1400 or 1600 revs. I initially suspected the idle speed control valve but after removing it and cleaning with WD40 the idle speed is slightly higher!

I removed the valve and applied voltages of 6V and 9V and the valve does move. The connector is supplying 13V to the valve so it looks as if it is being told to fully open.

Am I right in assuming that the only thing to suspect now is the ECU?
This model does not appear to have any other adjustment or electrical device that could be the culprit.

Any advice gratefully accepted. Rich

[Cougar 27]

My 480 Turbo was suffering from the same problem as yours; I tried the T.P.S and cleaned it with WD40. A slight improvement was made but it still was sticking at 1200rpm. Whilst trying to find the problem I removed my distributor cap, I found it was extremely worn. I replaced the cap and rotor arm (only £8). The problem has now disappeared and now idles at 850-900rpm.

Just a thought! …….

[Shady]

Thanks for suggestion, but I've already replaced the cap although I skimped and did not change the rotor arm. I will have to do the decent thing I suppose and go the whole hog!
I am now thinking about what could be telling the ECU to up the revs. This is probably the flywheel sensor but I don't know whether this sensor also feeds the rpm dial on the dash - if it does then it appears to be working fine. Next step may be to check the coolant temp sensor maybe it is telling the ECU that the engine is still cold so it opens up the idle valve.

Thanks for your ideas,
Rich

[Dan F]

If I remember rightly the Coolant Temp Sensor is one of the main culprits of this phenomenon.

Dan.

[Shady]

Thanks for suggestion. I managed to find the fault by checking the sensors one by one. The manifold air pressure sensor was stuck as I discovered when I checked the output voltage. A good tap with the blunt end of a screwdriver put it right. The sensor was telling the ECU that the inlet manifold air pressure was low and so the ECU told the idle valve to open to allow more air into the manifold.

An important lesson I have learnt is that the ECU diagnostic will not flag up a sensor reading as a fault if it is in the operating range of the sensor even if it is incorrect.

Rich