Hi,
This is actually for an Acura MDX and recently when I was logging some sensor data using an obd2 reader I found this weird issue with timing only at idle.

MDX has DIS and its a 3.5L V6 engine. I understand that normal timing at idle is supposed to be 10°±2°, and it is indeed 10° after the engine has warmed up. But on a cold start it behaves very odd. It starts off in the negative (sometimes as low as -3°) and stays that away even as the engine warms up and the idle settles down. As soon as it is shifted into gear (either R or D5) the idle timing jumps back to normal. Even if it is shifted out of gear back into P or N right away, the timing still remains normal. Its as if the gear shift is a triggering event for something that brings the idle timing to where it should be.

I have attached a chart. This is a plot of RPM, Timing and Intake Manifold Pressure(kPa) across time, taken off an obd2 reader. Timing is yellow, Red is RPM, Blue is pressure. Right scale is rpm and left scale is both timing and pressure. Moving from left to right direction on the chart notice how the timing starts off under zero. The first spike is when I quickly taped the throttle. The rpm briefly rises to ~2200 and alongwith it the timing shoots up to ~30° too and the pressure drops. As soon as it settles down the timing drops back to 0 and the pressure rises. The next significant change is when I shift the car into R (from P) and in about a couple of seconds shift it back into P. Notice how the timing jumps back to normal and stays that way. Pressure drops and stays that way too.

Does anyone have any idea what might be going on ? I find it hard to believe this could be normal. Something's definitely not right. What perplexes me is the how are shifting and idle timing related ?
Could it be a vacuum leak somewhere ? Or the IACV ?
Any help appreciated!

 

what your describing is absolutely normal. The ignition timing in the negative that your seeing is a result of FIRE(fast idle retard exhaust) control mode that honda uses on some of their newer vehicles to speed up the warm up time for the catalyc converter to become functional sooner. The negative timing is there to ignite the a/f mixture ATDC so it is still burning during the exhaust stroke and continues to burn through the exhaust, all to bring the temps up. The catalyc needs to be heated up to a limit before it can begin the chemical reaction to reduce emissions.

 

Exactly what the man said
i would have said it too but it wouldnt have been fancy

itll been more like thats normal becuz car has to heat up, timing change to faster heat up car (cave man)

 

I wasn't aware of that. Probably the '99 accord does not have "FIRE" so it did not retard the timing that far on a cold start and that also added to the confusion.

well it's good to know. seems like there is very little or no information about it on the web. some searching revealed nothing. So is it proprietary to Honda ?? But then you'd think its simple common sense and all car manufacturers would do that ??
If you happen to have any links that talk about this please let me know...

 

Honda and Acura did a changed alot since then like change over to induvid, coils instead of a dist. allowing for other timing features

 

The 99 model had other methods of controlling low emissions during cold start. Fire along with new advanced control systems was introduced on selected 02/03 honda acuras to meet the new LEV2/ZERO Emission regulations. The first accord to use it was the 2003 model. This information is from training courses I attended a while back.