Timing and Idle Q


Damn...Tyler65's hot!
May 25, 2003
Vancouver, WA
Just curious, how badly can advancing your timing effect your idle qulity? I was at 12-13 and decited to play with it so I set it at 14-15 deg. My idle seems...inconsistant is the best way to describe it. It will cycle through a smooth lope to a chunky idle and back again (not sure how long a full cycle is, maybe a minute or two?). I also think I may have a vac leak but Im trying to eliminate possibilites here. Thanks guys :nice:
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The ECU has to relearn some stuff after changing it. Undo the negative battery cable for 30 minutes, then run it for 20 miles with the new timing, and see if it's better. If not, I'd back it back off.
and in general in my experience, the idle will get lower with more retardation and a little higher with advance.

make sure your balancer did not slip - that will skew your reference points.

good luck.
The battery has been unplugged several times for much longer so I dont think thats the problem. Also I put on a new balancer last summer so things are good there. :shrug: Maybe its just the vac leak...
a stockish motor should pull 15-20" hg at idle. I could be wrong (I post a lot), but werent you trying to track down a vac leak quite some time ago?

also, though it does not sound like it is the case, if you set your base idle too high, the puter will fight it trying to get the idle back down to stock trim. this can cause surging.

Some of your symptoms could almost be thought of as a surging idle - Jrichker's sticky at the top of the page might have some info.

I will also add that some folks report a hunting idle after the KAM has been cleared (battery disconnected for any amount of time) - it takes a bit for the puter to relearn where it wants to be. EDIT: Ourobos already made that point. My bad. :)

good luck bud.
Yeah Im still pulling around 12 hg with my HCI combo, never really got that fixed. I do have a hunting idle from time to time but what Im talking about is different. The idle can be at a steady 800rpm but if you listen and FEEL you can sence a transition between a smooth lope and a chunky-not quite right feel and back again all the while still at 800ish rpm. I dont get it. When I first got the car it never did that, nothing but a silky smooth lope. What does it feel like if you bend a rod or burn a valve? I still have that tick from #4 area (havent pulled it apart to check the lifters/rods/rockers yet) which started last year after a hard run.