Erratic Idle

[TexasRho83]

Not really a serious problem right now but I'm curious nonetheless:

I have the 3.2 SOHC V6 in my 94 (194k mi), and yes, it has the ticking noise (but not all that bad)...I noticed that while idling at a stoplight or in park, the RPMs would hover at 1k for a bit but sink below to 750 or so while the needle would 'bounce' a little. Also noticed my oil pressure going below 30 as it happened. I knew I was in need of a tune-up anyway so I pulled the plugs and wires and put in fresh stuff (noticed a couple of the plugs were in bad shape). Also found out I need to replace my valve cover gaskets as there is oil evident in a few of the plug ports (not really wanting to tackle that job yet). My fuel filter was replaced around 180k miles.

Anyway, after the tune-up I've noticed a significant change in idle behavior for the better...but it still does the aforementioned behavior intermittently.

Any ideas?

[soundrew]

I would check for vaccum leaks-- a likely cause of erratic idle. What did your old plugs look like? What color were they? Were they all the same?

When RPMs get that low (750), oil pressure will drop significantly. Remember, your oil pump is driven by the engine so it will vary depending upon RPMs. It should show at least 50psi when you are at speed (3000 RPM).

[TexasRho83]

Originally Posted by soundrew

I would check for vaccum leaks-- a likely cause of erratic idle. What did your old plugs look like? What color were they? Were they all the same?

When RPMs get that low (750), oil pressure will drop significantly. Remember, your oil pump is driven by the engine so it will vary depending upon RPMs. It should show at least 50psi when you are at speed (3000 RPM).

I was thinking dirty fuel injectors?

My oil pressure gets pretty low when I notice the erratic idle, however at cruising speeds (70 mph) it's usually at or above 50 psi. The old plugs were needing to be changed and there were a couple that looked unevenly worn. I changed those and the wires though.