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Old 03-11-2011, 06:21 AM
BigCo540i's Avatar
BigCo540i BigCo540i is offline
The Usual Suspect
Location: Richmond, VA
 
Join Date: Jul 2007
Posts: 2,713
Mein Auto: 98 E39 540i - 09 E90 328i
Bad electric thermostat causing rough or fluctuating idle-

I had a shop do a diagnostic on my rough idle issue and it threw a fault code for a faulty electric thermostat. The tech said the Tstat is telling the car that the temp is either hotter or colder than it actually is so the car is either adding too much or too little fuel which is causing the fluctuating idle.

They did a "smoke test" and found no vacuum leaks anywhere on or around the engine including CCV so vacuum leaks were ruled out.

Has anyone heard of faulty electric thermostat causing fluctuating idle issues?
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