Car loses power while driving

Alot of the things your mechanic did could have fixed the problem. That is a problem when you are just guessing at what is wrong.
First thing, do you have the sedan or coupe? Which engine? Just 4 cylinder or 6 cylinder will do after you say coupe or sedan.
If I understand your problem, it idles rough, and is slow to aclerate off of idle, but once you get it going, it runs good? If that is your problem, then it really doesnt sound like an ignition problem unless maybe there is some added resistance in some connections that the higher rpm voltage can over come (Probably not). Your car probably does have a distributor cap, and if there are some bad connections where the rotor sends the spark to the cap, it may give the symptoms you descride. I would have thought the mechanic would have checked this as one of the first things to check. Have uit checked, and replaced if it looks bad, and then move on to what else could cause this problem.
What it sounds like is that your fuel supply at idle is not being correctly controlled. Once you get out of the idle mode, it runs good from there.
I would see if your mechanic, or another mechanic can connect a fuel pressure gauge inline in the fuel delivery system and see exactly what the fuel pressure is doing when it is giving you trouble. Maybe you have a fuel injector that is delivering too much fuel, and making the car rich at idle, but as you get some speed, it needs more fuel so it runs better. When your mechanic replaced your spark pulgs, were any showing signs of burning rich? Maybe a little blacker than the others, or possibly fouled some?
A bad PGM-FI main relay is usually a cause of the engine cutting off, but I can theroize a remote crazy senario in which it could cause this problem. I only through that out as a really remote possiblity.

Lets keep our fingers crossed that maybe the IAC you had replaced was bad, and maybe the mechanic didnt know how to set it up properly. The only update I see is for the PCM, however it may have never been updated and maybe this will fix it.

Try not to think of it that way. The parts you had installed are all new now, and will probably last a long time before you need work again. Who knows, one of the parts the first mechanic replaced may have broken this week.

Hi there,

Re check the valve timing, check the comps and check the ignition timing, start here.

Mark (mhpautos)

Hi there,

Some fault codes will not bring on the ECU light, so get a scan done anyway. As for the Cat, if it is a few check and report get it done, but don't get caught out, as I feel you problem is not exhaust related.

Mark (mhpautos)

Hi,

Yes. Sometimes a scan will not show any code because the sensors are not fully defective, they are just providing a false reading whereby the ECU will think that there is nothing wrong.

You need to run the vehicle with scanner plugged in to check all the various sensors to see if they are registering correctly according to conditions.

Since you mentioned while going up hill the problem happens, I suggest you have a look at the MAP sensor.

It could be a bad throttle cable. Have someone step on gas pedal while holding it down, check and see if the throttle body butterfly is fully open. If not replace the throttle body cable.

Scan the ECU for any codes. You may have a sensor issue when the vehicle is cold.

Also, if you haven't done a tune-up in a while, that could be the problem as well. But first have the ECU scanned.

If your engine compression is good, check and test the following below:

Oygen sensor
Dirty fuel injectors (cleaning the injectors often fixes this).
Bad MAP (manifold absolute pressure) sensor
Bad TPS (throttle position) sensor
Bad or dirty MAF (mass airflow) sensor
Low fuel pressure (leaky fuel pressure regulator or weak fuel pump)
Vacuum leaks (intake manifold, vacuum hoses, throttle body, EGR valve)
Bad gasoline (fuel contaminated with water or too much alcohol)

Sometimes, what feels like a hesitation is actually ignition misfire rather than lean misfire. The causes of ignition misfire may include:

Dirty or worn spark plugs
Bad plug wires
Weak ignition coil
Wet plug wires
Cap and rotor

Note: If it doesn't apply disregard.