serious trouble??

Asked by Aug 13, 2010 at 09:11 PM about the 1986 BMW 3 Series 325es Coupe RWD

Question type: Maintenance & Repair

My kid just bought a 325 es. When I took the oil fill cap off while the engine is running the rpm dropped severly and the idle got real rough. When I put it back on the rpm goes back up and the engine smooths right out again..Am I nuts or is this an indication of major trouble ..like real bad valves. All the cars I've ever owned did not have pressurized air in the valve cover unless there was bad blow-by.
No blue smoke coming from the exaust so I assume the rings are pretty much ok. But I'm no mechanic. So whats up??

5 Answers

3,215

Many cars do this. I've had a couple car that even if you pulled the dip stick it would effect the running of the car. Some are real sensitive to oil pressure drop.

Thanks Matt. I don't see how oil pressure would affect idle speed or smoothness since the function of oil pressure is to pump oil to engine parts and less pressure would only mean less efficient oil delivery to those parts. How could a drop in pressure affect anything like compression , air/fuel mixture, spark timing, etc? Not argueing with you but what am I missing? Do you really think it is normal or should we dump this car before she blows?

3,215

You could do a compression test on each cylinder, also check for water in the oil or oil in the coolant for a possible head gasket leak. The older model engine had HEX head bolts that get brittle around 150k miles (maybe more) and can cause a leak. You could replace the head bolts to Star or Tork or Torque type head bolts before they get weaker and you blow the head gasket.

2,335

This is nothing to do with oil pressure. This is everything to do with the emission system. A loss of vaccum from opening the oil filler cap has direct and detrimental effect on the idle control valve and thus causes poor idling or even stalling of the engine in some cases. Along the same line, more subtle idling problem is most often a result of leaky cam cover gasket, a very inexpensive and effective fix, not that you have this problem anyway. In your case, there is nothing to worry about.

1 of 1 people found this helpful.
3,215

ICV is electronically controlled from the ECU/OBDI on these cars, not vacuum from the manifold.

Your Answer

3 Series

Looking for a Used 3 Series in your area?

CarGurus has 33,894 nationwide 3 Series listings starting at $1,209.

ZIP:

BMW 3 Series Experts

  • #1
    Tom Demyan
    Reputation
    5,410
  • #2
    Robert Charlson
    Reputation
    1,740
  • #3
    grolyate
    Reputation
    1,300
View All

Related Models For Sale

Used BMW 5 Series
458 Great Deals out of 16,366 listings starting at $995
Used BMW M3
25 Great Deals out of 1,816 listings starting at $5,495
Used Ford Mustang
332 Great Deals out of 41,500 listings starting at $1,488
Used Honda Accord
766 Great Deals out of 89,440 listings starting at $1,444
Used BMW 7 Series
119 Great Deals out of 5,216 listings starting at $3,950
Used BMW 6 Series
69 Great Deals out of 2,459 listings starting at $5,995
Used Chevrolet Camaro
358 Great Deals out of 31,467 listings starting at $3,495
Used Dodge Charger
305 Great Deals out of 35,594 listings starting at $1,999

Used Cars For Sale

2018 BMW 3 Series For Sale
29 Great Deals out of 7,806 listings starting at $29,994
2017 BMW 3 Series For Sale
133 Great Deals out of 3,176 listings starting at $23,925
2016 BMW 3 Series For Sale
35 Great Deals out of 1,083 listings starting at $14,688
2015 BMW 3 Series For Sale
177 Great Deals out of 3,540 listings starting at $13,895
2014 BMW 3 Series For Sale
224 Great Deals out of 3,723 listings starting at $11,979

Content submitted by Users is not endorsed by CarGurus, does not express the opinions of CarGurus, and should not be considered reviewed, screened, or approved by CarGurus. Please refer to CarGurus Terms of Use.