Q: Engine idle fluctuates

asked by on December 05, 2016

When you start the car it idles between 1000 and 3500 rpm's. Up and down. Up and down. After about 5 minutes it then surges to 5000 rpm's and would blow up if I didn't shut it down. I have replaced the iac valve and the map sensor neither of which has helped. I'm stumped. Any suggestions? Thanks

My car has 190000 miles.
My car has a manual transmission.

This may be a sign of a vacuum leak. A vacuum leak can be one of the most frustrating and difficult problems to diagnose. High idle speed is a common sign and stalling is another. Confirmation of an engine vacuum leak can be a very loud hissing sound coming from the engine area. When a vacuum leak is present in an engine, this causes an excessive imbalance in the air/fuel ratio which creates a loss of power and causes the motor to run at a much higher RPM as a result of the increased oxygen present in the fuel charge being injected into the motor. I would recommend having an expert from YourMechanic come to your location to diagnose your vacuum leak as these can be very difficult and time consuming to trace.

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