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Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 5 Series > E39 (1997 - 2003)

E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 03-11-2011, 05:21 AM
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BigCo540i BigCo540i is offline
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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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  #2  
Old 03-11-2011, 06:58 AM
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Nittenyadhav Nittenyadhav is online now
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This could be your MAF sensor. Mine has the same problem chnaged the MAF and all is fit and fine.
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  #3  
Old 03-11-2011, 09:12 AM
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bluebee bluebee is offline
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Dunno if it helps, but there are thermostat-related technical documents here:
- What is the temperature of the coolant & when the thermostat opens under normal conditions (1)
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Old 03-11-2011, 09:36 AM
edjack edjack is offline
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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
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Last edited by edjack; 03-11-2011 at 09:38 AM.
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  #5  
Old 03-11-2011, 09:52 AM
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BigCo540i BigCo540i is offline
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Ok... I'm installing the t stat tomorrow morning. If it still has fluctuating idle then maybe maf?? How do you test it?

Yes BMW spec.
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Old 03-11-2011, 10:05 AM
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Quote:
Originally Posted by BigCo540i View Post
maybe maf?? How do you test it?
Dunno, but these might help:
- Mass air flow sensor (MAF) and idle control valve (ICV) require periodic cleaning (1) (2) & buying a replacement MAF cheaper than the BMW MAF (RangeRover MAF) (VW MAF) (Hyundai MAF)
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Old 03-11-2011, 11:17 AM
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Where are all of these best links located?
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Old 03-23-2011, 03:41 PM
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Originally Posted by BigCo540i View Post
Where are all of these best links located?
This screenshot was taken at roughly 110K views; now there are about 130K views ... so a lot of people must be using 'em.

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  #9  
Old 03-23-2011, 07:23 PM
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BigCo540i BigCo540i is offline
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Quote:
Originally Posted by bluebee View Post
This screenshot was taken at roughly 110K views; now there are about 130K views ... so a lot of people must be using 'em.

5 views are mine.
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Old 03-13-2011, 06:58 PM
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*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.
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Old 03-23-2011, 12:30 PM
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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?
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Last edited by BigCo540i; 03-23-2011 at 12:50 PM.
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Old 03-23-2011, 02:35 PM
bobdmac bobdmac is offline
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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.
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  #13  
Old 03-23-2011, 03:35 PM
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I just met with the owner and we settled on $1600. One benefit of a local owned business and cash.
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Last edited by BigCo540i; 03-23-2011 at 03:37 PM.
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Old 03-23-2011, 07:51 PM
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540indiana 540indiana is offline
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I think a man of great wisdom or he may be full of chit mentioned that to you sometime last week about the intake gasket??? Congrats man, I'm glad you figured out the issue.
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Old 03-24-2011, 05:06 AM
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Your mention of intake gasket leak confirmed by spraying carb cleaner around the intake seals and getting fluctuating values on the GT1.

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.
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Old 03-28-2011, 04:52 PM
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*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.
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