Low Oil Pressure reading on dash and Dim Lights

[CulverC4]

Hey everyone,
I just started having an issue where my engine begins to idle rough as it warms up/sits idling. As soon as I come to a stoplight for example the idle will be fine at first but will begin to gradually roughen the longer I sit in gear, foot on brake. The interior dash lights and headlights will also begin to dim and the car will sometimes go down to 500 or so rpm. I also noticed that the car's in-dash oil pressure gauge will read as low as 9-10 PSI. The funny thing is when I start her up when cold the revs at idle will read around 700-900 rpm, oil pressure will read around 40 PSI, lights don't flicker and acceleration from stop seems stronger. Also, sometimes the flickering lights situation/weakened acceleration/rough idle will "magically" disappear for a while, then it will return if stopped in gear for too long. I recently had the intake manifold gasket, valve cover gaskets and fuel pressure regulator replaced. Also, the rotor was replaced as one of the pins broke off inside and the engine was misfiring for a couple hundred miles (one of the cylinders wasn't getting spark). A local corvette shop replaced the rotor and replaced 2 wires with AC Delco wires, but the rest are aftermarket wires, could this have something to do with it? Also, there is one vacuum line that is disconnected, it's near the accumulator. My old auto shop teacher from high school hooked up his real time scanner and we saw the coolant temp sensor spike on the graph, he said it might indicate a damaged CTS. A buddy had the same problem with his Denali (flickering lights) and a new battery fixed the problem. I think I replaced the battery about 1 1/2 to 2 years ago. Before I take it into the shop I'd like to be slightly prepared, any ideas guys?

Thanks in advance,
Jose

 

[John Robinson]

Ideas

First the oil preassure from what you say is OK. It is normal for the pressure to drop down at idle especially when it is up to full temp. The time to start to worry about it is when it does not go up as engine comes off idle.

As for the rough idle and dimming light's Several things come to mind lthat could cause that .

1. Bad ground
2. Bad battery (I know you think it is not that old but have it checked)
3. Vacuum leak somewere
4. EGR hanging open at idle
5. TPS (Check for correct voltage values)

That is the short list I am sure others will add to it.

 

[air1jpg]

I'd have the alternator checked if the battery is ok.

 

[vetteboy86]

I think your fast idle should be higher. Not sure exactly what that is on an 89 but that seems low. Your oil pressure is low at idle as well. I know, this has been discussed before, so someone will have a different take on that.

Do you have any stored trouble codes?

 

[CulverC4]

I should probably have indicated that the temp here in southern california is pretty warm for the most part (+60 degrees year round), don't know if that has anything to do with the high idle issue being low, but she will idle at 900-1100 on some mornings. Never really paid too much attention before though. I haven't had the car scanned so I wouldn't know about any trouble codes, although the check engine light has not illuminated at any point yet.

 

[vetteboy86]

Could be possible the light is inoperable. I would have the check the codes on the car. It is fairly easy to retrieve codes from an OBD1 system. Can be done with a paper clip and about two minutes.