Testing Ecu Output

[BigMo82]

I have been having issues with rough idling for a while but what I have noticed is that if I turn my lights on the idle seems a little better. It still drops every now and again but it generally sits around 800rpm. I have been thinking maybe it's an issue with the ecu output to the throttle body as its completely electronic.

Does anyone know how I could test the ecu output to the throttle body to see if the voltage being sent into the TB is steady when the car is idling?

Thanks

Mo

[closchkutza]

There are 2 correct/normal idle values:

- without consumers (lights, AC compressor, rear windshield defroster, etc): 650rpm +/- 50 rpm;

- with consumers (any of the ones mentioned above): 750rpm +/- 5- rpm.

If your car has developed a rough idle you should try and locate the cause and not to try and mask the effects.

[BigMo82]

Thanks for your reply. I am trying to find the cause so I want to check the electrical current input to the throttle body to be sure it's not the ecu.

Thanks

Mo

[closchkutza]

Have you eliminated all other factors that can cause a rough idle (ignition system, vacuum loss, compression loss, etc)?

[BigMo82]

Thanks again for the reply, I have had the car compression tested and 1 cylinder was down 15psi compared to the other which the garage said was acceptable. Also had it smoke tested and there was 2 small leak points which were tightened and rechecked but this hasn't resolved the issue. Also throttle body has been taken off and cleaned and even exchanged for another from the breakers with the exact same results. Spark plugs are new and ignition coils have been tested using 2 different types of testers and appear to be working.

Thanks

Mo