Low Idle / Low Oil Pressure
 

I have a 2005 Silverado, 4wd, 5.3 v8, - getting low oil pressure indicator: pressure drops to about 10 pounds, can rev the engine and pressure raises to normal (35-40); while driving, pressure runs normal. At idle speed. rpm is dropping to about 500 or less seems to be when oil pressure drops. Put it in neutral and rev the rpms up to 800 or more and pressure comes up to normal. Appears that the engine rpms are what is causing the oil pressure issue. What all could be causing low idle? The engine runs smooth, replaced plugs and wires but no change.

How many miles are on the engine? 35-40 psi sounds a little low to me at driving speeds. Mine is at 55 at driving speeds. Higher rpm's will give you more pressure but 10 at idle is too low.

does the engine has active fuel management/displacement on demand?

240,000 miles on the engine. but I don't think the problem is necessarily due to high mileage engine wear. the low oil pressure issue came on "over-night" - I would think pressure loss due to bearing wear should be gradually increasing over time. 2 months ago (+/-) I took it in for oil change (valvoline 5-30 same as always) - about 2 days later is first time low pressure light came on - didnt do it again for maybe a week, then started getting more frequent - I had another oil change about 3 weeks ago - however, no change to low pressure at idle. I am losing a quart between 3000 oil changes - but not dripping - (no oil spots in the driveway).

I am not sure if it has that or not: how can I check?

if it has the afm option, there is a oil pressure relief valve in the oil pan. If stuck open you will have low oil pressure to the lifters and the oil pressure sending unit located at the top back of the engine.

I just checked...that option wasn't available for 2005.

I had not heard of that - but sounds like something similar may be happening. I don't have oil drip spots, but am losing a quart between changes (no signs of burning oil on plugs or exhaust pipe) so I am thinking it must be blowing out when engine is under pressure.

according to gm, they do not consider 1 liter consumtion over 2000 miles to be xs ive.

you will have to have the oil pressure verified. This will rule out a bad pressure sending unit or confirm an actual pressure problem. Its not knocking right?

I've had 2 different shops look at it - both confirmed that the sending unit is ok. The engine is not knocking. It's just at idle when the engine rpms drop down to 500 or less that the oil pressure drops - as soon as I give it throttle and rpms come up to 700-800 then the oil pressure goes up to 35+/-. Thats why I think the oil pump itself isn't the problem. I'm thinking something is causing the engine to idle slower than it should, which in turn is causing the oil pressure to fall. The second shop I took it to checked the fuel system pressure, and said it was good. The truck has EFI. Just thinking out loud here - could it be an air intake issue - the paper filter is only 6+/- months old, but maybe something blocking the passage to the throttle body? The fuel filter is in the tank - either pull the bed or drop the tank to get to it - I don't want to but will if that's what it takes to beat this thing. And by the way, thank you for the ideas and the help - it is very much appreciated.