Sounds like a car before OBDII. get the code read or
read it on the light with the appropriate jumper.
Your computer's adaptation strategy was interrupted.
The voltage spikes are not good for the computer. It is like it learned bad information and cannot forget.
You need to fully maintenance battery, clean in the connections at the posts, tighten them. protect them with noco washers first, and coat them with sealer after.
Then, you must run adaptive strategy resetting the throttle hard stop.
If you dont know what I am talking about, you can operate every function and drive in town and on the freeway.
If the hard stop setting is too high or low.
Ask for help at a shop. it takes a few minutes.
They may recommend inspection, and or tune and maintenance items before the idle adjustment.
Other cars have isc motors, idle tracking switches, or idle air bypass valves.
Clean, adjust, test and if necessary, replace throttle related sensors and or actuators.
Be sure codes are not set.
If so, address them.
Adjustment for hard stop is supposed to be done by an emission repair tech as his last thing before the drive tests.
Technicians with certification for engine performance and driveability are the best to ask about poor idle quality.
They have schooling and testing as well as experience.
They will not break laws about emission controls and they always try to get you the answer based on what year, make, and model car you have. Testing and awareness of bulletins and emission related updates is their job.
They don't usually have alot of time to mess around, so let them do their basic diagnosis and it will serve you well as the consumer.
Ask the dealer of the car to check the idle speed sensor inside the throttle body.
Its called "hunting"the engine fuel/air mixture is set to lean,IF the car is old 15+years its just simply 1/4-1/2 turn of the mixture screw in or out depending on the model.If its a newer model vehicle ,you need take it to your local garage,where they will plug it in to a diagnostic computer ,and find /fix your problem.
Youve given very little info,,it could even be lack of service,blocked air filter ect ,Im a certified mechanical engineer with 30,years + expeariance,but without more info probly correct.
Is this an older car? The idle may be set too low and the engine is feeding itself fuel to continue running. The vehicle may need a tune up.
I've the same problem with my Toyota Carina ED 1992 with 4S EFI engine. I'm planning for a tune up, with oxygen sensor replacement and fuel injector cleaning.
I had a car that did that... turned out to be the power brake vacuum booster. It had a leaking diaphragm which created an engine vacuum leak when i stepped on the brake.
Several things can cause this; Get it checked out on a scanner ! PROBABLY the 02 sensor !
Take $20 to any OIL CHANGE PLACE and have your IDLE AIR CONTROL VALVE and THROTTLE BODY cleaned out
Its "searching" you need to get the Throttle Positioning Sensor checked out.
running too lean. most like an intake vacuum leak.
Because it wants to race.
look for a vacuum leak.
Make, model, year, mileage?
