![]() ![]() The result is an automatic feedback loop that helps maintain a constant idle speed. When the idle speed drops, the timing advances, increasing power and moving the idle speed back up. Setting up your timing like this has a stabilizing effect on the idle. The 3d view below shows a spark table set up this way. The timing in this row can be bumped up by around 2 to 4 degees over the idle timing. Then you can add a row around 300 RPM below your target idle speed if you find the idle to be unstable. Ideally, you’ll want the timing to be set to slightly below the timing that would give it the most power – on most piston engines, this typically works out to somewhere in the 10 to 18 degree range. Timing is a very useful tool for controlling your idle speed. If your idle hunts when the engine is cold, but stabilizes when it warms up, try more warm up enrichment. You’ll need to make sure the air/fuel ratio is maintained during cold start. Batch fire engines typically idle best in the mid 13’s, so if you’re leaner than that, put in some more fuel and see if that stabilizes the idle. ![]() So, if your engine is batch fire, you’ll need to add a little more fuel so all the cylinders can stay at 14.7:1 or richer. Batch fire engines, however, have issues at idle with intake pulse reversion sending some of the fuel into an adjacent cylinder. On an engine with sequential injection, this is simple enough – get the engine idling at 14.7:1 for gasoline, and you’re good to go. ![]() Correct FuelĮngines don’t like to idle lean a lean air/fuel ratio is one of the biggest causes of a surging idle. These problems should be addressed individually. To get a steady idle, you need three things in place: correct fuel, correct timing, and correct airflow. This may seem counter-intuitive, but consider this: If the engine is idling at constant load with the throttle held at a constant opening, shouldn’t you have a constant idle speed? If your idle surges or hunts under these conditions, and your idle control valve is staying at one opening value, the idle control settings are not the problem. The first key may surprise many novice tuners: The idle control settings are not the most important thing to adjust to get a smooth idle. “How do I get a smooth idle like my stock ECU had?” It’s a common enough question to warrent a small article with tips for how to get the idle in tune. ![]()
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