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Heavy Idling

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Not familiar with your choice of words. Exactly what do you mean by "heavy idling"?


Drive your car.

Use your cell phone.


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When I am sitting at the light I feel my engine knocking. Dont know wht wors to use. Its not smooth untill I accelerate. Just had my sparks plugs changed, changed my fluids and added a fuel additive. I felt this issue before the tune up. I thought the tuneup may help but it did not.

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Please check your car's diagnostic codes and report them to this site. Following is a how-to:


All the dash lights will test and certain codes might display. There may be both current and history codes to note.

Generally speaking, fuel additives have not proven to improve any engine condition and can damage the fuel pump. Perhaps you could note what you used.

How did the old plugs look, (platinum pads on yet, sooty?), how many miles on them? Most importantly, what plugs did you install - hopefully original GM.

What is the RPM at idle? This can be checked by stepping through the INFOMATION button.

One way to check a significant knock, (if suspected at a piston/rod bearing on one cylinder), is to disconnect one spak plug at a time. However, this will also cause a rougher idle and may confuse the issue.

Have you or anyone else listened to other areas of the engine bay for the source of the knock? It may be as simple as an exhaust pipe bumping on the body/frame.

How many miles does this engine have and do you know of any major repairs?

Good Luck.

Add power to leave problems behind. Most braking is just - poor planning.
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For a knock that is not a pre-ignition knock, first check the motor supports. the front one is the most likely to go, and the torque wishbones on top of the engine on each side that link to the radiator supports are next. If the rubber is knocked out of either torque wishbone, change them both; you can do it yourself in a few minutes. The front lower motor support is best changed by a mechanic with the car raised on a rack.

If you have a knock at idle but not when driving, a good candidate is cross-firing between the plug wires, or even plug wires connected to the wring cylinders.

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