BimmerFest BMW Forum banner

Bad electric thermostat causing rough or fluctuating idle-

12K views 15 replies 6 participants last post by  BigCo540i 
#1 ·
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?
 
#4 · (Edited)
The two issues are not related. The code suggests that the heating element in the t'stat is burned out, or there is a fault in the wiring. Get it sorted out before the heater shorts out and damages the DME.

Was this a BMW specialist? If not, best to find a good one. www.bimrs.org
 
#6 ·
#8 ·
*UPDATE*

Ed you are correct that the two items are not related.

Good news- I replaced the thermostat earlier today and the code for faulty electric thermostat did not reappear. Took me about an hour and a half, I did not remove the aluminum throttle elbow but if you are going to do it this way you need a good swivel socket set. A hook tool is also handy for prying the lower hose off the tstat. I couldn't find mine so I used a small Allen wrench and vise grips to hook the hose and pull it loose.

Bad news - fluctuating idle still there. I'm going to replace the CCV next.
 
#9 · (Edited)
Well it turns out that I have a leak in the intake gaskets that's causing all of my rough idle issues.

I was quoted $2100 for the shop to replace spark plugs, Intake gaskets, Valve cover gaskets, Valley Pan gaskets, Rear ball joints, rear brake lines, bleed brake system, and CCV.

I know this is all DIY type stuff but does this sound like a fair price?
 
#10 ·
For all the stuff that you mentioned, I think that's a fair price, providing it's done correctly. The valley pan gasket and rear ball joints in particular are time consuming. The CCV, spark plugs and intake and valve cover gaskets can be done in concert with the valley pan gasket. Others can speak to the issue of brake lines, but I doubt they're a large component of the costs.
 
#15 ·
Your mention of intake gasket leak confirmed by spraying carb cleaner around the intake seals and getting fluctuating values on the GT1. :thumbup:

I found out that spraying carb cleaner to find leaks doesn't necessarily raise the idle to a point that you can notice without the proper equipment.
 
#16 ·
*UPDATE *
Rough idle solved. Just got her back from the shop and everything is running great. They put florescent dye in the oil and coolant that will light up with a certain type of light if any leaks were to appear. 2 year 24 month warranty on the work.

The inside of my engine was really clean with no sludge and hardly any wear on the cam lobes and chain guides. Synthetic has done its job for 150k mi.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top