Idle problems on a carbureted engine are usually very easy to find and fix. At the most, the throttle shafts are binding and would create the need to replace the carburetor. At the least, the choke is stuck on and holding the fast idle cam up and that would cause a high or erratic idle. A physical inspection is needed to determine what is causing the high to be too high or too low or erratic.
On a fuel injected engine, high or erratic idles can be caused by a bad idle air control motor (IAC) or in Chryslers case, an air idle solenoid (AIS). Other common things that cause your idle to be too high or too low are vacuum leaks like bad throttle body base gaskets and broken vacuum lines, bad throttle position sensors (TPS) , fuel pressure too high, leaky fuel injectors, bad coolant sensor (computer thinks the engine is overheating so it speeds up the idle) bound up throttle linkage or minimum idle settings have been tampered with taking the control of the idle, away from the computer.
When a tech begins to find the cause of the idle problem, he or she will typically check for computer codes which will help guide him to the area the computer thinks the problem is rooted. They will check the tailpipe readings and see if the engine is misfiring or running to rich or too lean and they will do a visual inspection of all the related sensors and their connections as well as all the vacuum lines and connections.
As with all repairs, there may be three portions of this type of repair bill. There may be a portion for the diagnostic time, a portion for the defective part and the labor to install it. It could also be as simple as finding and reinstalling a vacuum line for $25.
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