Strange timing issue at idle - need help.
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Junior Member
Joined: Nov 2006
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Strange timing issue at idle - need help.
Hi, this is my first post here.
This is 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!
This is 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!
Thread Starter
Junior Member
Joined: Nov 2006
Posts: 2
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the only noticeable 'problem' that prompted me to look at what's going on at idle on a cold start was a slight rough idle.
besides that the only other 'indication' was a very obvious change in the sound of the engine as soon as I throw it in gear and out at idle.
besides that the only other 'indication' was a very obvious change in the sound of the engine as soon as I throw it in gear and out at idle.
Last edited by accord-mdx; Nov 24, 2006 at 03:43 PM.