1999 Ford Escort idle problems

If it idles high, with it in park, block off mouth of throttle body with something, it should kill the engine. If very little or no effect on idle, you have false air getting in there from somewhere.
Make sure throttle valve is closing, where applicable, take throttle cable loose, see if idle returns to normal. Check and clean idle air system. Any applicable trouble codes?

I see this is an older question, but in case someone is having the same problem, here goes.
Besides the things above, I'd pull a spark plug, check it. Could just need a tune up, or you could have just a single cracked plug. One bad plug or bad spark cable will cause what you described. I always like to start with the simplest/cheapest solution. A tune up with new cables won't hurt anyway.

Try cleaning the throttle body and check the gap on all the spark plugs also all electrical sensor plugs and battery terminals this could be related to engine temperature also if to hot rpms stay up longer to cool off but maybe your idle air control valve is bad when did it start?

Fuel blockage / starvation / faulty fuel pump.

Replace fuel filter

When was it last tuned??

did you replace the line filter,it may be cloged.

the first thing u need to do is run a key on engine on self self test to see if the problem is with the idle speed control motor. any shop with a good scanner can preform this test, let me know the code they get.

The CAMshaft position sensor is faulty.

Could be vacuum leak or bad ignition wire(s).

I had a similar problem on my "93 Ford probe. The engine idled pretty rough with shakes, Turned out to be a head gasket leaking engine coolant into the cylinder during low rpm's. At fast rpm's it was fine becuase the internal cylinder pressure was greater than the hot coolant pressure & would prevent the coolant from leaking in.

A friend has the same problem with his "94 Blazer 4.3 L, throttle body injection, manual tranny. He hasn't fixed it yet, It started a few weeks ago & is getting worse. His gets a fast idle with hiccups which causes the engine shake. He already checked the EGR valve. He also has a severe exhaust problem, Not oilly but very gray & terrible smelly, but only when the fast idle problem happens. THis fast idle hiccup problem starts when the engine is warmed up.

The IAC valve is usually the problem with the 1.9 Escorts ,causing a very poor engine idle at a stop. It is located on the side of the throttle body .

1.6 zetec surely ,for this year