Saturn sl2 rough idle wont accelerate. We replaced the timing chain, spark plugs, air filter, TPS sensor, and changed oil. We check the coils, plug wires, fuse block, and negative ground. Problems started leaving work. started fine, went to accelerate from the parking spot and it killed. Wouldn't idle or start. We made the above repairs and now it will idle but wont accelerate.

Needs a tune up. Adjust engine timing, replace plugs and plug wires, replace air filter, oil and oil filter, fuel filter and clean fuel injectors, adjust valves.

If it is not firing on one cylinder, check and eventually replace distributor rotor, or electronic injection module.
Check also for camshaft problems.

What engine do you have? is check engine light on? You said you changed coil pack, but what about spark plugs? could be fouled by normal wear, improper application/plug gap, oil fouling (oil residue on electrode) caused by bad valve guide seals or bad piston rings or gas fouling(electrode wet with gas) caused by bad plug, wire, injector, O-2 sensor. Could be caused by a vacuum leak (hose or intake manifold/gasket) Check all vacuum hoses for cracking/chaffing, repair as needed. with engine idling spray carburetor cleaner at base of intake manifold watch for rpm increase if so there is a vacuum leak. Could be stuck open egr valve, Could be compression problem or timing chain problem. This is the best I can do with info you provided. Hope it helps.

Change the gas (and the oil, with Synthetic). The gas loses it's volatility after just a few months and starts to go bad. Siphon all the gas out and put in a fresh tank. Let us know if that helps.

TPS sensor and IAC sensor.

Three things you should check using a good code checker which can read sensor outputs - the throttle position sensor (TPS), the mass air flow sensor (MAF) and the EGR valve. While you are at it, replace the PCV valve.

2006 3.9 has to be a T-Bird or LS

There are no spark plug wires

It has Coil-On-Plug individual coils

Plugs don't fail --they get changed at 60,000 miles
give or take,say every 3 years

The front (2) O2 Sensors get repalced at 100,000
miles. The ones closest to the engine

Clean MAF Sensor at least once a year

I have no idea how you inspect a pcm,if your
at home & have no scanner or PC Based Software

Egr Valves fail early on those & other fords

You could test,not look at,actually put an oscilloscope
on the TPS Sensor

Any oil on a spark plug requires a new valve cover gasket

If a coil was replaced based on a code alone,you may have
replaced a good one,not what needed to be replaced if any

I am having the same issue on Mitsubishi Galant 02. Clattering on acceleration, herky jerky idle. Pulled a code multiple cylinder misfire. My mechanic's diagnosis is bad valve cover gasket causing oil to seap into the spark plugs and bad timing belt, which I have not replaced at 150k miles. I do however know my fuel injectors do need cleaning, he hasn't ruled that out either. Have you pulled any code on it? I have read on engine knock sensor going out on some of these also. Hope this helps some.

I would look at the egr system. First pull the valve and clean it. If you have a vacuum tester this would be a good time to test the valve itself as well. When under load you should be able to see the diaphragm engage and hold and then release as you release the vacuum. If that doesn't work check and/or replace the egr solenoid. It's located on the driver's side of the valve cover and usually runs about 60$.

Yours is a common complaint and the above is the most common remedy. Outside of that you might want to check and clean the idle air control valve and the port where it's housed. If it is extremely dirty or something managed to get stuck in there that could affect you vehicle running at idle as well.

Another thing, even though you just changed the plugs, pull one back out and look at it. If is fouled with oil you might need a new valve cover gasket which if it's leaking badly enough will impede spark.

check timing belt!! good luck!!