Hesitation and pulsing rough idle on cold start?
2012 Honda Civic, 165k miles. Been having a lot of hesitation off the line (picking up speed from a stop). When slowing down from 5mph to 0mph, and while stopped, my idle is rough and "earthquakey" in bursts.
On cold starts my car idles rough and feels like a pulsating feeling like the car's going to die. RPMs on cold start are 1500 and take 10minutes to drop to 800.
No codes, shifting is smooth. Any ideas?
You may have multiple issues on a car of that mileage… Has a tuneup been done? Check/test the IAC, TPS and MAP sensors and related circuit wiring and for any vacuum or air intake leaks. Pinch off vacuum hoses at manifold ports with a pliers one at a time and see if idle improves or spray carb cleaner around hose connections or TB/manifold sealing areas with engine idling. If idle speed alters, it indicates a vacuum leak… Repair as needed. Check air intake ductwork for any cracks, splits, looseness.
The IAC is used by the computer to control idle speeds at closed throttle which can get dirty/clogged up over time and not respond properly and the TPS and MAP sensors tell the computer the throttle angle and manifold pressure which are needed to determine and control idle speeds and gauge engine load. Hesitation from a stop is usually or often a bad TPS or MAP but could be other issues. If the sensor data is bad, you can wind up with erratic /high or low idle or lag/hesitation while driving or poor power, poor fuel economy, etc. Other devices or systems such as EGR or cannister purge valve can also be defective which can cause the issues you have… Or weak fuel pressure, clogged injectors/bad spray patterns, etc. Some issues may not trip a trouble code if a device is operating within parameters but still wrong for actual engine conditions. And it's normal for the engine to idle slightly faster on a cold engine but 1500 rpm's sounds a little high. Add some Seafoam or Techron to the fuel tank per label directions to clean injectors. Or have them tested/cleaned for proper spray patterns.
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