In October 2014 my mechanic replaced the intake manifold on my car. (leaking antifreeze). Head was checked (machined?) and the head gasket was replaced. Since then, the idle (which normally stays at 700-800 rpm) occasionally drops to 400 RPM and then back up to normal. It does not stall. It happens at stop lights and the like. Today he replaced idle air control valve. Problem is exactly the same. What else can we do?
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Re: How can my mechanic fix intermittent idle drop?
Throttle position sensor, or MAS. Mass Airflow Sensor on the air intake (air filter housing) case. Possible vacuum leak. Ensure all vacuum lines are connected and in good condition. The smallest pin hole will make the biggest difference.
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Your intake manifold may be cracked. It is plastic and is know to cracking. If you take a flash light and look behind the intake, you should see a small puddle of antifreeze or a slight crack. You will need to replace the intake manifold and the gasket, possible do a complete head job on the car since it is already leaking through.
Sounds like antifreeze leaking in to me. Ports at rear of intake are trick and easy to get that gasket mis-aligned. Hate to say it but when you take the intake back off I imagine the culprit will be obvious. Only other thing is that the intake wsa fine and you actually had a blown head gasket.
You really won't know until you take the intake off. There could be other problems that caused the leak before the intake cracked. Until the intake is replaced you won't be able to do a pressure test of the cooling system. Make sure the thermostat is replaced since it could have been damaged from the overheating episode.
Hello roxanna surf: My name is Roger and I will help you. The problem could be one of several problems. GM has a problem with the intake manifold gaskets leaking coolant useually external but can leak internal also. Check at the corners of the intake manifold where the manifold meets the heads. If you see green or orange drops of coolant or a slimmy build up than the intake manifold gasket is leaking. Idf the leak has been ongoing for some time and the engine has overheatedI would also look at a head gasket, warpped head or even a cracked head as a source of the problem. The engine does not like extreme heat and can have serious issues. Should you need further help please just ask. Please rate the answer. Thank You for using Fix Ya. Roger
Hello, Probably the easiest thing to do is drain the oil and see what it looks like. If it is okay, then invest in a new oil pressure sending unit and change the oil filter. For awhile there were bad Fram filters and others with bad relief valving in the oil filter.
If the oil has Antifreeze in it, then it is pretty much a given that a head gasket is bad. You should check your sparkplugs anyway for signs of water/antifreeze contamination if the engine is blowing the Antifreeze out of the exhaust. This can help show you if only one head gasket is bad or if both are bad.
I hope you either bypassed the heater core or fixed it. Another gasket that can get Antifreeze into a cylinder is the Intake manifold gasket. The newer cars usually have only air coming into the engine through this manifold. You need to look at where the top Radiator hose enters the engine. If the hose enters on the block, you are probably good for the Intake gasket.
But if the top Radiator hose attaches to the Intake manifold, a loose Intake can leak Antifreeze into the heads through the ports on the Intake. It can also cause a lack of power and poor idle. If the Intake gasket IS your problem, the head gaskets can be fine. The Intake gasket is reasonably inexpensive.
I can tell you that a loose Intake can be checked for air leaks by running the engine and spraying a water mist from an old detergent bottle around the seams of the Intake. The engine speed will change or stall if the water is drawn in. The Antifreeze leak can not be checked by this method.
If you have the V-8 Engine, just totally disregard this post.
If you have the 3.8L V-6 engine, your oil consumption problem is most likely to be caused by the PCV Valve if you cannot find any external leaks. These are also known for the upper intake plenum leaking antifreeze. The ports in the manifold that go to the throttle body are made of very thin plastic. The EGR tube, with its hot exhaust gasses, goes right between them. This causes the plastic to heat up and crack, causing an antifreeze leak that goes directly into the intake and gets burned in the combustion chambers.
DORMAN makes a replacement upper plenum kit to fix this problem. The kit includes the upper plenum with thicker coolant passage walls, an intake manifold gasket set, a smaller-diameter EGR orifice, and a new PCV Valve. This kit will probably fix BOTH of your problems.
The DORMAN part number for your car is 615-180 Shop around...prices vary considerably.
First is to check to see if it's your intake gasket, pull the dip stick and look at the condition of the oil. Look for excessive sludge and milking, look under the oil cap and look in to the valve cover, also pull the PVC valve and look at the condition. Check to see if there is sludge and milking, if there is then you have antifreeze leaking in to you engine crank case which is very bad. The antifreeze is corrosive to the engine bearing and will soon cost you a new engine if there is no indication of antifreeze in your crank case, then it's a leak somewhere else through out your cooling system. If you see the leak from the out side then that's good, it may just be a bad hose clamp that needs to be tightened. If your not sure and want to buy some time, add about 3 table spoon of common kitchen Black Pepper. The black pepper will work it's way throughout the cooling system and will plug up the leak for now and the great thing about pepper is that it will not leave any residue when you flush out the system, not like the radiator stop leaks out in the market. Good luck and keep me posted, it could be the heater hose to the heater core.
You may have a lower intake manifold gasket leak (or a head gasket leak-slightly less probable) the lower intake can leak onto the serpentine belt and fling oil (and/or antifreeze). The lower intake manifold gasket is usually the culprit here. There is much information about changing it if you are inclined to do it yourself. If not, expect around 800 to 1200 to fix at dealer/mechanic. This is usually accompanied by (but not always) oil in the antifreeze, or antifreeze in the oil...