I noticed my idle goes up and down ever so slightly to the beat of the hazzard lights. I'm wondering if anyone knows if this is normal. I mentioned in another thread that my idle sometimes surges a little after coming to a stop as if I tapped on the gas. Some forum members suggested it was a problem with the car's computer. Could this be related?
I think there is something strange happening with the
ECU
. If Im at idle and depress the accelerator ever so slightly, the RPM starts slowly pulsing up and down. Do you get that? I dont think the hazard lights have any bearing on it other that the frequency is similar.
I've seen both of these things in my 07 cs. After reading this thread, I tried out my hazzards for the first time and the tach needle was certainly moving -- though I couldn't detect a difference in the sound of the engine. It could have just been due to the pulsing current draw affecting the electrical tach guage.
The "oscillating idle when slightly depressing (and holding) the throttle open" thing freaked me out a bit when I noticed it last week. I'm glad to hear that its systemic and not just me!
Hazards vs. RPM
I suspect that you are simply observing the varying load from the alternator causing the engine RPM to shift, followed by the ECU doing it's best to compensate. The 4 way flashers are lighting up around 55 watts of lamp on each corner of the car, roughly 18 amps of current. This load causes the alternator to become harder to turn, which in turn loads the engine. In the days before ECU engine control you would see a much more significant change in RPM. Now the ECU is going to notice that the RPMs have dropped, so it's going to add a bit more fuel to return the RPM to where they are supposed to be. All of this takes a fraction of a second to adjust, only to have the flashers turn from on to off or vice-versa causing yet another readjustment. If you can only detect a very small change in RPM, then things are perfectly normal.
Doug
