QuestionI have a 1992 Hyundai Sonata SE V6 at a cold idle and if driving while not warmed up for at least 15 to 20 minutes the idle will jump from 1500 to 2000rpm as it starts to warm up it will jump from 1000 to 1500rpm until it is running at a warm tempurature and stays in the 900rpm range. Once the car is at this warm stage it stops surging. I have just purchased this car and don't know the full history on it and was not told about this problem before buying.
Any ideas and thank you in advance.
AnswerAs I recall, I've seen two types of problems cause a surging idle. Unfortunately, I've never seen either associated with engine temperature. Regardless, I'd recommend checking for the following:
-- Things that cause the idle switch to not read correctly. This switch is on the throttle body, has one wire going to it, and should make electrical contact with the thottle body when closed. This simple to test with an ohmmeter (or test light attached to the positive battery terminal) when the throttle is closed.
-- The idle switch could be out of adjustment. Adjust via the nut on the switch.
-- The throttle cable could be too tight and not allowing the linkage to contact the idle switch. Usually, when I've seen this, there's a problem with the idle system and a mechanic (or someone else) has attempted to adjust the computer controlled idle by adjusting the throttle plate opening by pulling the cable tighter.
-- Things that cause excessive air to enter the engine, causing it to run too fast.
-- This can be caused by a defective idle actuator.
-- This can be caused by a base idle screw misadjusted to the point that the idle actuator cannot compensate.
-- This can be caused by a vacuum leak at the manifold, PCV hose, brake booster hose, or other area.
