low oil pressure indication and idle speed

[Dash01]

When my low oil pressure indication comes on, it's always when slowing or stopping and the idle speed has dropped to ~700 rpm. Adjusting the throttle cable for higher idle speed gives temporary relief.

Have others experienced this correlation between low idle speed and low oil pressure indication, and then been able to remedy the low oil pressure indication by cleaning or replacing the idle control valve?

[Jr ///M5]

It helps to know what model of car you have....there are problems with V-8's where the oil pump bolts back out and fall into the oil pan, then there are problems with the oil canister on the 6's, not to mention the banjo bolts that back out on the cam oil spray bar for say the 535's.....

Do a pressure check with a gauge, at idle the oil pressure can be as low as 7 psi and not trigger a light. If you're triggering a light at 700 rpm, that's not good. If idle is down, have you checked the basics? Air filter, plugs, etc?

Jr

[Dash01]

It helps to know what model of car you have....there are problems with V-8's where the oil pump bolts back out and fall into the oil pan, then there are problems with the oil canister on the 6's, not to mention the banjo bolts that back out on the cam oil spray bar for say the 535's.....

Do a pressure check with a gauge, at idle the oil pressure can be as low as 7 psi and not trigger a light. If you're triggering a light at 700 rpm, that's not good. If idle is down, have you checked the basics? Air filter, plugs, etc?

Jr

It's a '90 535i with good plugs, new spray bar with tight banjo bolts and rebuilt head with new valve guides, new oil pressure sender, new camshaft, new rockers, good valve adjustment, etc..

Idle speed should be a bit higher, and when the throttle cable is adjusted to that effect, the oil pressure light does not flicker. So, I'm wondering if the lower-than-correct idle speed can be adjusted and corrected, which in turn would pump oil pressure up a bit, and the oil light would stop flickering.

As idle control valve controls idle speed, perhaps this is the source of the mystery?

My old oil pressure sender was implicated in low oil pressure flickering, until I took it out and wiped it off, then stuck it back in for another 6 months of proper oil pressure indication and carefree motoring.

[genphreak]

Most likely its idle speed. Spec is 800-850rpm for M30B35. You need to fix that first.

1. Change the oxygen sensor if it proves sus- (test it first), they are easily damaged by incorrect gasket goos and coolnat getting into the exhaust gases- and age and poor running. It's the first thing I'd measure if I were sure there are no intake leaks, esp. if the engine has been running badly or the head gasket has been changed.

2. Measure the output of the temp sensors- they too are critical.

3. Find a copy of the TIS and follow the procedure to set the gap on the Throttle butterfly- and adjust the TPS at the same time.

3. Again use the TIS to set the Carbon Monoxide (idle air flap bypass orifice) ie 'CO' screw. Do not adjust the AFM unless you have to, it is the last link in the chain- and must be treated with extreme respect. If it has been opened by someone else, or the grommet is missing from the CO screw- that's a good sign. If so, get a megasquirt or a MAF kit.

Nick

[Ross]

To be safe temporarily install a mechanical gauge and see what you get.
If pressure remains low you probably have worn bearings or a tired pump.
I've seen lots of motors given new life by replacing these items when the warning start to appear.

[genphreak]

To be safe temporarily install a mechanical gauge and see what you get.
If pressure remains low you probably have worn bearings or a tired pump.
I've seen lots of motors given new life by replacing these items when the warning start to appear.

M30B35 pumps are extraordianarily reliable- and $400 to replace. I've suspected mine for a while now due to noise. Best thing to do is stick a gauge on and keep an eye on the actual pressure in all scenarios before going to the trouble of finding out you over-reacted... the canister is well-known to cause low pressure for the first 10 seconds however- I suggest u check the write up on www.bmwe34.net

[Ferret]

I had the same problem in my 525i - turned out to be a bad oil filter.

I was wrecking oil every 1k due to the high compression head - and the filter was getting full of crap...

Have you changed this recently?

[Dash01]

Yes, just changed the filter, BUT this was after I briefly ran the engine under light load with 1 qt. of ATF in the oil to clean out the crud, then drained it and replaced with proper quantity of 20W50 oil. ATF, by the way, definitely does clean out the crud.

I'll pull the filter and have a look. Could be, not all the crud got flushed out and is now in the new filter.

The anti-drain check valve in the oil filter housing is OK.

[Martin in Bellevue]

Yes, just changed the filter, BUT this was after I briefly ran the engine under light load with 1 qt. of ATF in the oil to clean out the crud, then drained it and replaced with proper quantity of 20W50 oil. ATF, by the way, definitely does clean out the crud..

Think the ATF moved enough sludge to block the oil pump pickup? It might be time to drop the pan for a look. Avoid the cork pan gasket if doing this; napa has the preferred rubber gasket.

[Dash01]

Think the ATF moved enough sludge to block the oil pump pickup? It might be time to drop the pan for a look. Avoid the cork pan gasket if doing this; napa has the preferred rubber gasket.

In my '90 535ia there was not much of any sludge in there before I did the ATF trick, per inspection and biopsy done through the oil level sensor hole. Dark stains to be sure, but no thick or gooey crud whatever before I ATFed the engine. Just to be safe, I'll probably do this again.

The ATF pretty much removed the oil stains from the underside of the valve cover, making it look like new. I only ran 1 qt of ATF + topoff of new 10W40 in the engine with a new filter for a short time, under light load, then drained and replaced with 20W50 and yet another new filter. Methinks the occasional flickering low oil pressure light is primarily a function of low idle speed (~600-700rpm) on coasting to a stop after the engine is warmed up. This never happens when the engine is not at full temp (oil still thick) or when not coasting to stop. Could be, the brand new oil pressure sender is a wee bit off. Blip of the accelerator pedal stops the flicker, but I worry anyhow.

BTW, is there any cheap and commonly available (i.e., NAPA, etc.) oil filter out there, so I don't need to mail order from BMA, etc,?