An abrupt change in engine speed is probably the most common problem with an internal combustion engine. There are several reasons contributing to this problem. Let's take a closer look at them.
After several years of car operation, a problem such as floating revs is often encountered. The engine starts normally, but instead of a gradual decrease in speed as it warms up, the speed drops sharply. The turnover changes abruptly in the range of 1400-500. Gradually warming up the car, these "dips" disappear, the engine will stabilize until the next "cold" start. But over time, this effect intensifies.
The reason for all this is the engine temperature sensor. The best solution to this problem is to replace it.
Often, the speed jump in engines with electronic fuel injection, this is due to abnormal air leakage. The fact is that such engines have a control unit (computer). Its task is to calculate the amount of air entering the cylinders. And also while monitoring the states of several more sensors, open the solenoid valves of the injector for a while.
When excess air comes in, the throttle sensor signals that it should not be. And the temperature sensor "says" that the engine has already left the warm-up mode and the fuel needs to be consumed less. As a result, the computer starts to "go crazy", he does not know where to put this extra air. Because of what there are jumps in speed.
In engines equipped with carburetors, the reason for the floating speed may be an incorrect adjustment of one of the servomotors. It opens and closes the throttle valve on certain occasions. To fix this problem, it is necessary to unscrew the adjusting screws of the servomotor, in which the drive jerks in time with the speed surges.
This malfunction occurs only if, you yourself tried to regulate something. In diesel engines, the cause of this effect (spikes in speed) is a sticking of the moving blade in the feed pump. This is only due to the water present in the fuel, which causes rust to form. This usually happens with machines that have been idle for a long time.
