Noise under intake manifold

Oil in the coolant is usually an intake manifold gasket problem on these engines. If a head gasket failure the engine will normally overheat and give erratic temp guage readings. Make sure the oil level is full. Is the rattle noise coming from the engine? Some times the exhaust (converter) will fail and the catylist will seperate causing a rattle noise from the exhaust and plug it up giving a no power situation

Check the vacuum hoses for leaks. Follow them around and make sure they're all connected and not worn out to where they had fallen off due to the hoses being old and worn out. Take some soapy water in a spray bottle and spray mist the intake and see if the idle changes. Check the big hose coming from the brake booster to the intake and make sure it's connected and in good shape. Basically check everything for vacuum leaks. It sounds like that's what you're issue is.

hi Rachel.
see if this helps you out.
https://www.cargurus.com/Cars/Discussion-c2620_ds638555
or this one.
97 towncar engine noise under acceleration Lincolns OnLine Message Forum
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sounds to me like a heat sheild is loose on the fire wall or under the car

I don't want to deviate from what you described but are you sure its not comming from the catalytic converter. sometimes the plate get loose and rattles

In order of probability:
1 Muffler/tail pipe
2. Shock absorber (broken or loose bushing)
3. something (car jack) is loose in the storage pocked under the floor of the trunk - or in the side storage behind the wheel well in the trunk...
-Jim

it may be you have water and oil mixing together a crack in your head engine

if it's not running bad, it may be a simple crack in a pcv line, or a loose hose(vaccum). should be simple to fix.

Need to check for any loose belts first .

had the same issue, had someone look and it seems the noise was caused by heat shield being loose covering exhaust system. Have that checked out.