Rough ilde intermitent, idles smoothely, then stutters, then idles smoothly

Here are a few things that might help.
1. Check your spark plugs. make sure the gap is right and they are not worn out.
2. Check your distributor cap and rotor for build up on the contacts.
3. Check your spark plug wires, make sure they are on the distributor and spark plug tightly. also check them for damage ie. heat, knicks, scrapes, etc.
4. intake idle control valve. these do cause your symptoms and are easy to replace.

hope this helps ~ Zach

check for a vacuum hose leak ( brake booster , transmission actuator module, vent controls )

check out the idle air control valve and the passages

First thing I would do is change the fuel filter and air filter

Possible Idle air control, simple to change on the throttle body

Rough idle is a very common problem on 4 cylinders, but I believe the 98 Regency has a 6 cylinder in it, right?

Sometimes the coil packs get iffy, and sometimes the EGR Valve gets a leak in it causing a rough idle.

When the accelerator pedal is depressed, it can change things so that the engine seems to run smoothly.

However, I would look for codes to see if anything intermittent is occurring in the engine that may need attention.

The OBD-I scanner can help to diagnose the problem, if anything is out of specifications on the engine in question.

The owner will have to find a technician that has such a scanner.

ruff idle may b idle controll senc. ----tapping may be plugs-- wires, and or gas try 91 oct gas next 3 tanks and see thats the cheeepset place to start

put a throttle position sensor on the throttle boby this should fix the problem!

The fuel pump is on top of gas tank inside, you have to lower the tank, unless is mounted on gas tank side, follow fuel lines, thy are two, one main and one return, the fuel filter is on the main under driver

have this car taken to an auto repair and ask for a engine oil flush and engine oil change, that mught help