Fluctuating Oil Pressure and Idle

[livestrongroadie]

So I am new to this forum as well as owning an American vehicle, so please don't be too rough with me haha. Anyway, I recently received an 88 K1500 from a family member and am slowly trying to give it the TLC it needs as it has sat for many years with little usage. Truck has around 66k miles on it and has a 350 TBI engine and is automatic, not sure transmission code, again, new to the American made scene.
Anyway, as I have been driving it more over the past few weeks than it probably has been driven in the past year, I started to notice that when I let the truck idle while warming up and even after warmed up, the idle seems to be very "lopey"(if that is the correct terminology) and I notice the oil pressure also seems to fluctuate significantly in relation to the idle.
I haven't really had the time to look too deeply into this yet or throw parts at it, just wanted to see if anyone has any insight on common problems with that era 350 engine. Thought maybe this could be a common problem with a quick fix, but if not, thanks for any advice any one can provide.

 

[beardeddummy]

Sounds like a dirty throttle body and iacv

 

[livestrongroadie]

I was thinking throttle body possibly. I have a rebuild kit on the way, so I'll just do a rebuild and do one of those BG injection system cleaning kits when I do all the other things I want to do. Is the idle air control valve part of the throttle body?

 

[livestrongroadie]

Cleaned throttle body pretty good and problem has improved, but not gone away. Was planning to get a throttle body rebuild kit anyway, so guess I will give a rebuild a shot and see if that changes anything.

 

[Jrgunn5150]

It could be any number of issues, cracked vacuum lines, bad ignition component's, on and on and on. Good luck!

 

[kennythewelder]

The truck I have now, and the one I had before this one, both had fluctuating oil pressure. I developed a water leak on my 97 5.7L (350) (the truck I have now) The leak was where the head, engine block and intake manifold join together on the drivers side next to the fire wall. When I removed the intake manifold to replace the gaskets, I could not believe what I found in the lifter valley. It looked like black wax in there an was clogging up the flow passage ways for the oil to return to the oil pan,. I cleaned all of this out and did an oil flush after I pit the engine back together. I was using castor oil GTX for years. I will never use it again. Now take in to count, that I live where the weather gets hot very often, and this can brake down oil. Also both of my trucks idle smooth, but the oil pressure would still fluctuate. I now use Valvoline for about 5 years now and, have no fluctuation in oil pressure.

 

[michael hurd]

Very lopey, rough idle could be a symptom of a stuck EGR pintle.

Start engine, then carefully reach under the top hat and try to pull up on the diaphragm. If there is no change in idle characteristics and it seems stuck, chances are you need to replace it.

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[livestrongroadie]

Sorry, the holidays and work were murder on my time and I am just getting back to this issue. I tried the EGR test and pushing on the diaphragm nearly stalled the truck 3 consecutive times trying it. Wish it had been that simple. Have to check out a few more things i guess.=/

 

[Supercharged111]

The truck I have now, and the one I had before this one, both had fluctuating oil pressure. I developed a water leak on my 97 5.7L (350) (the truck I have now) The leak was where the head, engine block and intake manifold join together on the drivers side next to the fire wall. When I removed the intake manifold to replace the gaskets, I could not believe what I found in the lifter valley. It looked like black wax in there an was clogging up the flow passage ways for the oil to return to the oil pan,. I cleaned all of this out and did an oil flush after I pit the engine back together. I was using castor oil GTX for years. I will never use it again. Now take in to count, that I live where the weather gets hot very often, and this can brake down oil. Also both of my trucks idle smooth, but the oil pressure would still fluctuate. I now use Valvoline for about 5 years now and, have no fluctuation in oil pressure.

High ambient temps do not cook oil. Oil tracks closely with coolant temps and the only thing that takes it higher is extended high RPM. 250 is nothing, not even for a dyno oil. Most of the time, you oil won't exceed 220 anyway.

 

[kennythewelder]

High ambient temps do not cook oil. Oil tracks closely with coolant temps and the only thing that takes it higher is extended high RPM. 250 is nothing, not even for a dyno oil. Most of the time, you oil won't exceed 220 anyway.

If ambient temps don't add to the oil braking down and turning into a wax like cake, then what does ? I know what I found when I pulled my intake, and I know what oil I was using. I have also seen this with Quaker state oil doing the same thing. This is not something I have read, or something that someone has told my, this is something I have seen with my own eyes. My point is that if there is sludge in the oil passage ways, it can cause the oil pressure to fluctuate, because the oil does not flow back into the oil pan as it should. That is what happened to me in my truck. As I said, after cleaning out the oil passage ways once I removed the intake, O have no fluctuation in oil pressure. It has been at least 5 years sense I removed the intake, and cleaned out the oil passage ways, and I still have steady oil pressure at idle. One more thing to keep in mind, I bought this truck from a Chevy dealer after the original owner traded it in on a new truck. His info was still in the truck, along with some service tickets from the OE. when I bought it. I contacted him, and like me, he changed the oil every 3000 miles, so in the 227,000 miles that is on this truck, it has never gone over 3000 miles with out an oil change.