low oil pressure at idle

[gndi]

My 95 740's oil pressure warning light comes on at idle. I think the problem is low idle, currently about 1,300 rpms. My question is how do I increase idle speed? Thanks for any help.

[libertylover]

How do you set the idle speed? Basically, you don't, Mr. Computer is in charge. However, I think there are some specific idle electronics.

Anyway, an idle speed of 1300 RPMs is not low, in fact, it is high, quite high. Normal idle speed should be around 600 RPMs. My guess is that you have virtually no oil pressure at the normal idle speed and Mr. Computer has increased the idle speed so you have enough pressure to prevent damaging the engine.

Now, as to what causes the low oil pressure to begin with:

1- Make sure you have plenty of oil in the car. If you recently had it changed they may have only put 4-5 quarts in it. Your 740's V8 engine requires almost EIGHT quarts of oil.

2- Worn out piston rings but I doubt it unless you have tremendous milage on the car. You'd have a lot of bluish smoke coming out of the tailpipe and you'd notice.

3- Maybe a bad oil pump.

[gndi]

Thanks for the quick response. I probablly should have given more details on the idle problem. Idle is about 600rpm in neutral, but around 1300 rpm in gear at a full stop, which is when the pressure light comes on, once car is in motion and revs are above 1500 light goes off. Hope this may make a difference in solution to the problem. Thanks again for any advice. George

[libertylover]

George, that sounds like a pretty wierd problem.

Just curious, if you're stopped and at 1300 RPMs and shift into neutral, do the RPMs drop to 600? Also, you might see what happens when you select 4th gear instead of Drive. And another other thing, what happens when you select the snow mode? The reason I ask is that there is a transmission computer as well as the engine computer and I don't know how they interact. I'm still thinking the car is in a self-protection mode somehow. I take it you checked the oil level and it's OK.

You probably need to seek professional help and that's not me. I'm just a DIYer with a repair manual and a curiosity about how things work.

One other thought: your oil pressure may be fine but have a bad sending unit. Probably step 2, after checking the oil level, is to get a true reading of the oil pressure.

Please let us know what you find.