My valve covers have been leaking oil from the seals on both sides of the motor for some time now. Are there any symptoms that show up from a bad gasket besides leaking oil? The reason I ask is because I have had a low/rough idle for also for quite a while that I tried to fix by cleaning the IAC. That had very little effect on the idle. Could the valve cover gaskets be a cause of low pressure in the intake manifold?

I have replacement gaskets on hand but I have been weary of actually tearing into the motor to replace until now. I'll be doing it after the new years anyway. I am gonna check for vacuum leaks in the hoses soon too.

I am also suspecting that my cat is getting near the end of its life too with 210k mi on the odometer. I ran for a while with a bad O2 sensor, the engine overheated due to a failing water pump about 3 yrs ago and the dealer did nothing but replace it along with the timing belt. But I'll check into that after the checking for vacuum leaks and replacing the valve cover gaskets. In the mean time, does anyone think that this could be a cause for a low rough idle if everything else is in good shape?

 

Hard to Say--but what about oil getting on the O2 sensors. I dont like oil leaking--It is my pet peeve. When oil leaks--it degrades other rubber parts.

but rough idle--Do a leak down and see what you get--maybe you have a leaky valve?

 

I had a rough idle on my 95 4runner and toke it to the dealer. I had a burnt valve and was only firing on 5 cylinders. I had an oil leak as well. I am assuming from the valve cover. After the repair and $1500 later, the oil leak was gone. About a year later the oil leak returned. I am guesing again that it is the valve cover. I have heard that the head bolts get stretched and allow the gaskets to fail. I am debating whether to get new bolts and replace gaskets myself

 

before you replace the gaskets, you may want to ensure that the cover bolts arn't just loose. There was another post where some members were discussing that here.

 

So I never knew about leakdown tests until you just mentioned it. I am curious about making a tester and doing it myself but I am put off by the fact that you have to know how to find top dead center on the compression stroke for each cylinder. I don't know how, is it hard to do? Maybe I should just take it to a shop for the test since I definitely won't be doing the wrenching if there is something wrong with the pistons/valves or any significant engine internals....

I appreciate the help but I forgot to mention I have already tried and then cleaned all the oil off the engine but it came back eventually.

I am really interested in finding out if there are any other symptoms besides leaking oil or if bad gaskets lead to leaking oil and nothing else.

 

An engine fire. Oil has a high flash point but it does burn if it gets hot enough. That happened to me once...now that's a story. My engine overheated and caught fire. Then I got robbed and run over by the crooks with their car all in the same hour... I'm being a smartass but it's a true story.

Um, I'm guessing that if you don't have a tight seal on your valve cover it could very well effect crankcase pressure and vacuum and cause a rough running engine. The valve cover gasket is awfully simple to replace. Can't be that expensive either.

As far as finding TDC, check here. http://personal.utulsa.edu/~nathan-buchanan/93fsm/
Probably in there somewhere. I could describe it a little but I don't know anything about your engine. You could search for it. Basically you line up the O notch on your timing pulley with the distributor rotor pointing at the number one spark plug (disconnect your battery first!). You'll also feel a little puff of air coming out of the plug hole as right before you get there. That would mean TDC on compression stroke (cylinder is charged with compressed fuel/air and the plug is about to fire). After that you're just turning the crank a specified number degrees to the next pistons TDC, as per the O notch on the pulley. Something like that anyhow.

 

If you're going to go through the hassle of checking all the valve cover bolts, then just throw some new gaskets under there when you do because either way you're going to have to take off the intake manifold on the driver's side.

 

A leaking valve cover gasket usually means leaking spark plug o-rings and those will eventually hamper the spark energy enough to give you a weak spark or even a miss... especially at idle.

 

I just checked my valve covers today...only the bottom ones loosened over the 137K miles and 10 Years. Go figure. I would say that tighting all the most common loose bolts (lower ones) does not require pulling the intake.

 

Just a tip if you decide the do the valve cover gaskets. When you get to the driver's side, there is a harness in a plastic casing that runs across the valve cover. Before you take the cover off, wrap that entire piece in electrical tape. It will be brittle and will crack and break. Wrapping it will help hold it to gether and keep pieces from breaking and falling into your head when the cover is off. Ask how I know lol

 

Oh yeah, I think I remember reading your thread. You were the one who had the really clean motor when you took off the cover right? How is that thing still running?

 

Here is a ?... Does a leaky valve cover cause a burning smell that is pretty strong when you get out of the truck after a ride across town?

 

Yup you can smell the oil running down the head onto the exhaust. It runs great when it wants to. I know valve cover gaskets aren't related but it still has a rough idle, flashing CEL on the highway and seems to loose power. Starting to look for a Sequoia.