Ign Timing advancing durring timing check

[slipnfall]

Hi there, Just a quick question: what would cause the ECU to advance the ignition timing durring a timing check/adjustment? Warmed the car up, shut it off, unplugged TPS, turned it back on. When I view the timing w/a light, the timing advances from 20* to around 25-26*, and back to 20* about every 1.5seconds. If I plug in the TPS, the ignition stays firm at 20*. Idle is around 720-750 w/TPS unplugged, around 780rpm w/it plugged in.

Also should the timing advance when I increase throttle??(TPS plugged in) I know this isn't the 'base' timing, but is this reading the actuall timing at that point in time?

Any ideas?Thanks!-Jamie

[NISTECH]

no timing should not be on the move with the correct tps plug disconnected, Yes the timing does advance under acceleration.

[slipnfall]

Ok... well I know it shouldn't be 'on the move'. My question was what would cause the ECU to adjust it? I thought that unplugging the TPS put the ECU into open-loop, which should not adjust maps due to sensor inputs. This is different from the 'failsafe modes' outlined in the FSM, correct?(this basically just tells you what [sensors] can fail and allow the car to still function. They are TPS, CTS, MAFS, and ign signal.

So in open loop mode, what would advance the timing?:edit: also I have m/t, so I'm unplugging the only TPS connector, no hard open/closed switch like the KAE/auto :edit:

[NISTECH]

I dont know what would be moving it that seams odd, I have seen a sloppy chain cause movement. And for the record both the auto and manual have the hard contact switch but only the auto has the sweeping tps.

[slipnfall]

Well if increasing idle increases the advance, then it's probably just the idle is changing(duh, I can hear it), not the ECU changing timing. So the question becomes what control does the ECU still have over idle in open-loop? Is the IACV still operational? Maybe the 'warm-up' bimetal valve could be fluxuating... hmm

[NISTECH]

when you disconnect the tps Idle and advance computer controls cease. If its moving its mechanical. The IACV locks in a set position when it goes into base mode. btw open loop only means the ecm is not using the O2 to control fuel mixture ,instead it uses other sensors like the MAF,CTS,TPS hard idle/wide open contacts.

[slipnfall]

Sloppy chain? Hmm, replaced all my tensioners...

[NISTECH]

could be a warn dist drive gear. how does it move when it does advance is it steady adn smooth or is it irraticly jumping around?

[slipnfall]

The advance is pretty fast and steady: stays advanced ~1.75sec's, returns for about 1sec. I was able to get it to *not* advance once today. Right after I unplugged my MAFS(engine died), plugged it back in, and started it, it was steady. Tried wiggling the MAFS connector with no change. Unplugged my CTS, it bumped the idle up, plugged back in, timing was erratic again.

:edit: you said ecu has no control over idle/timing when in open loop, however unplugging my CTS changed idle, so it changed fuel delivery then, not air? :edit:

[NISTECH]

yes it richens it up when it goes in open loop, I think your confusing open loop with base mode here too.