How do you fix an engine when at shakes at idle?

Answer 1

An engine that shakes at idle is usually caused by something affecting combustion or airflow. The fix depends on the actual cause, but the most common ones are worn spark plugs, dirty fuel injectors, vacuum leaks, bad engine mounts, or a dirty throttle body.

I had a car that would vibrate badly whenever I stopped at red lights, but it drove almost normally once I accelerated. I first assumed it was a transmission problem, but after some troubleshooting and advice from a technician familiar with repairs at Bergman’s Auto Repair, the real issue turned out to be a cracked vacuum hose and old spark plugs.

A few practical things to check first are:

• Scan for engine codes
• Inspect spark plugs and ignition coils
• Look for loose or cracked vacuum lines
• Clean the throttle body
• Check engine mounts if the vibration feels heavy

If the shaking gets worse with the AC on or while stopped in gear, that can also help narrow down the problem. Catching it early usually prevents more expensive repairs later.

Answer 2

This can be caused by many different things. Here are the most common reasons, starting with the worst (and most likely roughest idling) problems;

Misfiring - Each cylinder needs, spark, fuel, and compression to run. If one cylinder is missing any 1 of these items it wont fire, or will fire poorly. Check fuel pressure and injector wiring, ignition wiring, spark plugs, and perform a compression test if the other items are fine. If a cylinder has low compression it will fire poorly, causing the engine to run rough.

Timing and Idle speed - The spark plugs needs to fire in time with the pistons for the engine to run smoothly, so check base ignition timing. The engine idle speed should be within OEM specs, check and adjust if needed.

Mounts - The engine and transmission mounts absorb vibration created by the engine that are felt in the body of the car. If a mount is broken, it may cause abnormal and/or extra vibration.

Vacuum Leak - Small vacuum leaks in the air intake path can cause 'fluttering' of the idle speed. The engine pulls in air that it has not measured, so the fuel mixture runs lean, causing idle speed to change. The computer compensates, and adjusts for the change, and this process repeats over and over, causing rough or 'breathing' idling.

Others - Bad wiring or bad sensors can cause the computer to miscalculate the fuel or ignition the engine needs to run properly. The computer could also be to blame, but isn't likely.

This is based on the assumption that you have a newer, fuel injected vehicle. If you don't have one, you either have a cool classic, or you need a new car....

Hope this helps.

-Nick