Need help with my engine!

Hi all,
I have a 1990 mighty max with the 2.4 4cyl engine. IT is in great shape except for a couple small things,

• Leaks oil from valve cover and into spark plug wells
• Starts up fine but after 2-3 seconds idle drop to barely running and then revs up to 3,000 rpm then back down again over and over until warm. Exhaust makes a putt putt sound during this.
• I can hear hissing coming from under the intake manifold, is this likely injector seals, manifold gaskets or what?
• Truck overheats up to 3/4 on the temp gauge but never past the white line into the red area.

any help you can lend is much appreciated. Thanks.

I should also note that i have checked for codes with a multimeter and got nothing.

A hissing sound from under the intake tells me the PCV hose might be off or cracked. Check that simple item first.

If, like my first wife, the intake is sucking from below, it must be a blown gasket...again, just like my first wife. Blow some cigar smoke down there when the engine's running. See if it gets sucked in or just simply satisfies the environment.

The extremes in idle lead me to think that there is serious vacuum leak.

The valve covers can be a tricky issue: too loose or too tight seems to allow leakage. Here's what I intend to do about mine: once I'm done fooling around with the top end, I'm sealing that sucker SHUT with silcone gasket sealer.

In addition to Roy's comments: Change your thermostat, You have a choice of a 180° or a 190°. Personally I like the 180 because it gives just a little more time when you notice the truck getting hot before it over heats.
To locate a vacuum leak, try a cigar and trace to the leak when it sucks in smoke from it. Get one of them raspy fat cigars that smoke a lot. If you have an electric fan, try to disconnect it for a bit so it doesn't blow the smoke away before you locate your leakage. This leak could be the main issue with your engine idle and racing. Intake leaks cause the engine to go lean and in turn will raise idle as it receives more air then fuel. This also will cause the engine to get hotter. Nothing worse then a lean running motor and like a 2 stroke, when it has gone past it's limit it will either just stop running or worse case, seize up. 4 strokes usually just get hot and eventually run out of fuel to run properly.
This is an extreme case to search for a vacuum leak. It's not a cigar, but you get the point I'm sure.
Attachment 11057
Our brakes use a booster that is attached to the firewall with the brake master cylinder. This item uses a large amount of vacuum and can also cause leaks. Usually noticed when applying breaks real hard and the engine will almost stall in panic stops. Just another place to check if you cannot locate your hissing sound.



Valve cover gaskets on our trucks are sort of trick to seal. Obviously you want to be sure the surfaces are both clean before your new gasket is placed. Usually in the back part of the cover is a half moon rubber insert that can dry out in time. Might want to replace it, if it is. Before placing new gasket, use high temp RTV in the corners of joints between the half moon rubber insert and usually between the head and timing casing and cam area housing. Spread the RTV so it doesn't end up all squirting into your internal engine oil to much. It can cause clogging if too much gets in.

Here is a sort of example, though it's the DOHC engine, basically it's the same idea.
Attachment 11058

Engine revving like you explained almost sounds like a choke plate possibly. Maybe observe the carburetor with air cleaner off and see what the action is down the barrels. If it is an intake leak, they usually get less noticeable as the engine heats up and expands to seal the leakage.

Good advice on all but the choke, as his truck is a 90 and EFI. If you don't like the cigar idea, use carb and choke cleaner around the intake and throttle, it will give a change in rpm with a vacuum leak, and will also clean up old oil leaks of the head and intake. Clean or replace the pcv and egr valves - never hurts to do this.