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Originally Posted by bimmern00b  Well now here's the thing. When the engine is cold it sounds fine and doesn't make itself known until I drive down the road a bit and when I turn the car off it sounds like something is depressurizing, sort of like a woosh of air or something... |
Can you isolate the noise to the back, front or either side of the engine? Does it fluctuate with engine rpm? Now that you mentioned the "depressurizing/wooshing sound", I'm thinking you might have a bad CCV (crank case vent valve) or a bad secondary air pump check valve orrrrrr a leaking secondary air pump. Here's how you could check each one of those things:
CCV VALVE - It's a black disc shaped plastic piece located towards the back of the engine up high, just to the left of the upper intake manifold. It should have a little slit on the bottom of it. With the engine running, place your finger over the slit on the bottom of the CCV valve, if you hear the whistle note change, your CCV is clogged. Unfortunately these things get brittle over time, so if you try to take it apart and clean it, it'll likely crumble in your hands. The part costs between 50-60 bucks new.
SECONDARY AIR PUMP - This is a black pancake shaped plastic valve located just aft of the airbox. There's two hoses going to it. One goes to the airbox, the other is a rigid plastic line that goes across the front of the engine compartment to the secondary air check valve. The secondary air pump is composed of a stack of disc-shaped plates that are held together with 6 aluminum rivets. Over time, these rivets break and allow the plates to separate which in turn allows the pump to leak. The pump ONLY RUNS FOR THE FIRST 30 SECONDS after a cold startup. So to check it, wait until morning or after the car has been sitting for several hours. Pop the hood and be ready to run around and stick your hand near the secondary air pump IMMEDIATELY after starting the engine. You should hear the pump running. If you feel air blowing on your hand, your pump is probably leaking. You can easily fix it by removing the pump assembly and replacing the broken rivets with nuts/bolts.
SECONDARY AIR PUMP CHECK VALVE - this is a black disc-shaped plastic piece located on the front passenger's side of the engine compartment just aft of the radiator fan. It'll have a rigid plastic hose going from it across the engine compartment to the secondary air pump. This valve should only allow air to travel in one direction, from the secondary air pump into the exhaust stream. With the engine warm, but not running, squeeze the two tabs on one end of the plastic hose and pull it off either the check valve or the secondary air pump. If you disconnect it @ the valve, make sure the hose is secured so it won't get tangled in the belts or fan. If you disconnect it @ the pump, take the same precaution as to not let it get tangled in the belts or fan. Start the engine, then feel if air is being pushed back through the plastic hose or the check valve itself. You shouldn't feel any air at all and if you do it may be hot so be careful. If you do feel air, your check valve is bad.
INTAKE BOOT - You should also check your intake boot for cracks, they're known to split at the seams and it's usually invisible to the naked eye. The best way to check it is to buy a can of brake/parts cleaner(NOT CARB CLEANER). With the engine running, spray a sh!tload of brake cleaner on the intake boot. Try to get it up underneath the boot as well. This is the ribbed rubber boot, just aft of the MAF sensor and airbox. While you're spraying brake cleaner on the boot, listen to the engine rpm's. If you hear it fluctuate, usually it'll rev up really high, then you need to replace your intake boot asap. You can temporarily fix it with duct tape. Just wrap the heck out of it to create an airtight seal. Note; you should also spray brake cleaner on any vacuum hoses as well as around the upper and lower intake manifold especially where they connect and mount to the cylinder head. Same thing, if the rpms rev up, you know you have a leak.
WATER PUMP BEARING - Grab the water pump pulley and try to wiggle it. you shouldn't have ANY play whatsoever.
Hope this helps, best of luck!