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idling problems, open/closed loop operation, timing


Dec 29, 2007
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Somerville, Victoria
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Hey everyone,

I've been working with Jason on this one but he's offline now so I thought I might just put this out there and see if anyone can come up with some ideas.

Here's the story: I have a 5ltr Calais, and at this current point in time it has a custom memcal - but i have no idea what's on it. It seems to run ok, little bit shaky, lacking a little down low, and it goes twice as good when it's cold outside but I guess that's the same for all cars. Most importantly it idles fine. Now, I had Jason do me up a chip, but as soon as I put it in my car didn't idle properly any more. It drops (to maybe 600, not entirely sure), almost dies, then revs up to over 1000, then drops back down and just keeps doing that. Sometimes it even stalls (especially if you give it a rev and just drop it). Jason told me to do a couple of things - like clean the IAC which made no difference, and to also check the timing. Now I finally got around to getting a timing light, and I checked my timing with extremely strange results. I checked it using both chips just to be sure as well. My results:

Using the chip that's currently in the car - engine at operating temp, white and black wires on aldl bridged: timing on the following mark:

Am I just seeing things, or is the base timing set at 16 degrees!? Also, I checked the timing without the connector bridged, and it stayed at 16 degrees - no advance at idle (no idea about other RPMs though).
I then checked it with Jason's chip, again, bridged it was 16 degrees, but then unbridged it was much further out (normal I guess).

Clearly my current chip has some real strange **** on it...

First question (Jason's probably the only one that car answer this anyway :p), but if the base timing is set at 16 degrees, could this be causing erratic idle on the new chip? It's still erratic even with the connector bridged and the timing fixed at 16 degrees, so I'm afraid that even if I set it back to 10 degrees it'll still be bad. I don't really know how the system works though, so I may try this sometime. Just wish the distributor wasn't so hard to get to.

Now, off to some other ideas that I've been thinking about. My car does have LPG, and the check engine light has been popping up a bit with the oxy sensor error code. I went out and bought a brand new oxy sensor, but the damn code just keeps popping up. I heard this does happen with gas, but I've been doing some research and I'm thinking there might actually be a problem with the reading somewhere. You see, with the current chip, on a cold start, it keeps the revs at about 1000rpm. and it's running smooth as a babies bottom. then after a couple of minutes, the revs drop to 700-800 or so (hard to tell on the crappy tacho), and it's a little bit rougher (but the idle speed stays constant). I'm assuming that this is change from open loop to closed loop operation. I must admit though, it definitely does sound rougher when this change occurs.
NOW, it has been a while since I did the same thing with Jason's chip in the car, but from what I remember, on a cold start the thing would be idling fine, until it hit that time or temp limit and switched into closed loop operation. Then it would start idling stupid.

Perhaps there's an issue with the oxy sensor, or other sensor readings? And the chip that's currently in my car has been modified to simply make the car idle better, but the problem hasn't been fixed? How can I check operation of open/closed loop? How can I check the signal for the oxy sensor? I do have a couple of ideas - I should reset the computer, then only drive the car on petrol and see of the oxy sensor code comes up.

The other more simple idea was that it could perhaps have a small cam that I don't know about. We really don't know at this stage.

But any ideas on the weird idle with a properly made chip would be appreciated. And Jason, I really know that I should give you a copy of my chip so you can see what's on it :p


on holiday
Jul 8, 2008
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well the chip you have might have the same idle advance as what the base idle is set at would stop it from moving when you disconnect the aldl bridge wire.or the est temp could be turned up higher than the engine temp at the time stopping it from getting any advance too.and it might be getting rough when it hits the est enable temp when it finally warms up thats what the roughness will be caused by ide say.closed loop shouldnt happen at idle.ide set the base back to 10 if you are running anything over stock timing in the memcal which you will be.