Loss of oil pressure at idle

adlegs

Original poster
Member
Dec 11, 2011
3
I own a 2002 Envoy and have been having idle issues for a few years now. 2 years ago I replaced the plugs with OEM and cleaned the throttle body and the idle seemed to get better but has been really bad for the last year or so. In the past week the oil pressure has become an issue at idle. I was only at 50% of the oil life from last oil change?? The pressure is good until the engine gets to normal operating temp. then I the pressure drops at idle only. I have noticed that if I keep the idle around 900 rpm the pressure is good but currently the idle is around 600 rpm. I sat in the car and studied the pattern of the low pressure warning. At idle with AC on idle at 600rpm the engine is idling rough but idling then feels like the engine stalls momentarily and the pressure drops the 5-10psi for 1-2 seconds the "Check Gauges" light comes on and "Stop Engine" shows in the display. Then the idle recovers and the pressure is normal(40-42psi) With the AC on this happens every 5-6 seconds, with AC off every 10-12 seconds. I have been reading this forum about this issue so this week I had the engine flushed professionally and the oil changed. After the oil change still having issue. Yesterday I removed and cleaned the Camshaft Actuator Solenoid and Throttle Body and yes I had the battery disconnected for over 30minutes while I cleaned both. I still have the issue!!! The next thing I am going to check is the oil pressure sending unit and have another oil pressure gauge hooked up to see if the pressure is really dropping. Can anyone help with this issue?? Any suggestions?? Thank You in advance for any replies.
 

christo829

Supporting Donor
Member
Dec 7, 2011
462
Fairfax, Virginia
What's your mileage? I'm assuming you have the I6. What did your CPAS look like when you
took it out to clean it? Screens intact? Did you see any seepage at the electrical connector?
How did the screens look after the flush and before you cleaned it? If there was a lot of buildup,
there may be debris still in the system that allows the condition to persist.

Since the oil pressure senders in the I6 are just switches, yours may be failing, so it'll
be good to get the real readings from the gauge you hook up. I suspect that it's not actually
the problem, just influenced by something else. When the idle drops, it gets close enough
to the cutoff pressure of the switch that it triggers the low pressure indicator.

It's possible for the CPAS to be failing and not show any physical indication, and it will
cause idle fluctuations.

Do you have a scan tool that can read pending codes? You might want to check and see
if you've got anything that hasn't tripped the light sitting in there, possibly for the camshaft position
sensor.

Good Luck!

Chris
 

adlegs

Original poster
Member
Dec 11, 2011
3
Big thank you to everyone. It was the pressure sending unit. I changed it and the pressure is good. I still have a rough idle issue but it is no longer effecting the oil presssure. Now I can move on to the rough idle isssue. Thanks again!
 

adlegs

Original poster
Member
Dec 11, 2011
3
christo829 said:
What's your mileage? I'm assuming you have the I6. What did your CPAS look like when you
took it out to clean it? Screens intact? Did you see any seepage at the electrical connector?
How did the screens look after the flush and before you cleaned it? If there was a lot of buildup,
there may be debris still in the system that allows the condition to persist.

Since the oil pressure senders in the I6 are just switches, yours may be failing, so it'll
be good to get the real readings from the gauge you hook up. I suspect that it's not actually
the problem, just influenced by something else. When the idle drops, it gets close enough
to the cutoff pressure of the switch that it triggers the low pressure indicator.

It's possible for the CPAS to be failing and not show any physical indication, and it will
cause idle fluctuations.

Do you have a scan tool that can read pending codes? You might want to check and see
if you've got anything that hasn't tripped the light sitting in there, possibly for the camshaft position
sensor.

Good Luck!

Chris



Thanks for the reply Chris,

The CPAS looked OK there was some buildup on one of the screens but not too bad.(second from the end) it was brown so I soaked it in carb cleaner and scrubed it lightly with an old tooth brush. Should I still check for codes? I dont have any of the check engine lights on. Should I change the CPAS anyway? Thanks for the feedback!
 

RayVoy

Member
Nov 20, 2011
939
Your first post suggests, that the bad idle started when the plugs were changed :undecided:

It has been reported (by many, many owners), that the I6 engine only likes AC-Delco plugs, if you some other plug, try changing to the Delcos.

And, I like to change the front (if your vehicle has 2, and these trucks do) O2 sensor. It will become "lazy" with age and can cost you mpg. changing it when plugs are changed, is a good way to remember when it was changed.
 

christo829

Supporting Donor
Member
Dec 7, 2011
462
Fairfax, Virginia
berto1014 said:
I'm a noob, what is CPAS? :confused:

Also where can I buy some good O2 sensors, and how hard are they to DIY?

CPAS is the camshaft position actuator solenoid, part of the variable valve timing system.

As far as O2 sensors, stick with AC-Delco. Some other makes may not match well with the parameters
our PCMs look for as far as heater response. I got mine from RockAuto on sale, but you can get them at
just about any brick and mortar or online store around here (I'm near Washington DC).

Easy or hard is a bit subjective. Get a sensor socket and some PB Blaster and that will usually make
life easier. I find them no worse to change than the spark plugs, but YMMV. :wink:

@adlegs...if you don't see leakage at the electrical connection of the CPAS, you're probably OK with
keeping the one you've got.

Cheers-

Chris
 

xxfile

Member
Dec 28, 2011
10
Every once in a while and very unpridictably i have a rough idle issue.
it will idle really slow like 600rpm and then stumble and sometimes stall while coasting to a stop sign.
stopping and restarting the engine and it goes away and may not happen again for 2 weeks or 2 months...
when the idle drops that low it gives the low oil pressure warning and that may be what shuts it off the whole thing seems related to the idle issue not the oil pressure issue at least it is for me.
 

RayVoy

Member
Nov 20, 2011
939
It sounds like the classic "I need to clean my throttle body" problem.

There is a "how-to" in the Articles section.
 

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