My vehicle surges at low rpm. There are no vacuum or fuel leaks and a new IAC made no difference. I did note a sizable dent in the steel fuel line. Will a restriction cause this?
Anything is possible. Did you disconnect the battery to reset the computer after replacing the sensor?
- Pull and check all the spark plugs to make sure you don’t have a cylinder specific issue. A slight miss on a v8 is more noticeable at lower rpms.
- Spark Plug Diagnostic Chart
From the Manual:
Base idle speed is controlled by the engine controller (computer).
Unlike carbureted vehicles, the fuel injected engines covered in this manual do not require idle speed adjustment checks as a part of a regular tune-up. In fact normal idle speed is NOT adjustable and should not be attempted.
This adjustment is the minimum idle speed with the Automatic Idle Speed (AIS) closed.
- Before adjusting the idle on an electronic fuel injected vehicle, the following items must be checked (and corrected, if necessary):
- AIS motor operation
- Engine vacuum and/or EGR leaks
- Engine timing
- Coolant temperature sensor operation
- Connect a tachometer and timing light to the engine, according to the manufacturer’s instructions.
- Close the AIS by using ATM tester C-4805 or equivalent, and ATM test code #03.
- Connect a jumper to the radiator fan, so that it will run continuously.
- Start and run the engine for 3 minutes to allow the idle speed to stabilize.
- Check engine rpm and compare the result with the specifications listed on the underhood emission control sticker.
- If idle rpm is not within specifications, use tool C-4804 or equivalent to turn the idle speed adjusting screw to obtain 790-810 rpm. If the underhood emission sticker specifications are different, use those values for adjustment.
If idle will not adjust down check for binding linkage, speed control servo cable adjustment or throttle shaft binding.
- Turn the engine OFF, then disconnect the tachometer, reattach the AIS wire, and remove the jumper wire from the fan motor.