what ECU does?

ECU have all the program to control ur engine from spraying fuel to spark plug ignition to mivec controls.

There are a few inputs and outputs to the ECU, mainly the inputs will be.. Throttle position sensor, o2 sensors, crank sensors, cam sensors, air flow sensors, knock sensors and etc.

Output will be throttle body valve servo, mivec adjustment valve, injectors, spark plugs..

basically the ecu has all the reference in the ecu memory itself. At what rpm, what load, whats the air temperature, how much throttle opening.. It will calculate base on the reference (or more commonly known as map) and fire the spark n fuel injector accordingly.

So what is closed loop or open loop?

Closed loop, the ecu will read the feedback from the sensors and make it adjustment accordingly. To make it as close as what is being commanded by the ecu. (the output is not always same as the commanded, example u ask it to do a AFR 13.5, but the output maybe 12.5, so the ecu will reduce the fuel injected to try to get it to 13.5).

Open loop, the ecu does not care the actual output, it will juz fire according to the map. Some ecu can have both state.. At WOT (wide open throttle, it will go open loop, something like that)

Now.. What is Remap? What is piggyback? What is standalone ecu??

Remap, a process to optimize the "reference table" within the map.

why some car can be remap and others cant?
Now, think that the ecu is a computer. The map is stored inside a CD within the computer. Some computer comes with Cd burner some only comes with cD reader. Those with CD reader wont be able to rewrite the content within the CD. And the CD must be a Rewritable type. So what does rechip means? Rechip is replacing the CD with a different CD (altered content)

Now the problem. Becoz ecu runs in closed loops nowadays, the information alter by the piggyback will cause a diff output. Example AFR will be richer.. But the ecu is expecting it to be leaner.. the feedback recieve by the ecu is diff hence it try to adjust itself to get the correct figures.. Slowly it will offset it back to normal. Worst case is the tune get too much of a diff the ecu cant return it back to normal it will think there is problem with the sensors hence throwing engine error codes..

SC changed lower arm bush for both front and rear with no questions. The noise reduced. But issue remains.

I've noticed (need observer driving behind) that the rear suspension's bottom mounting point vibrates vigorously when going over uneven roads. Comparing to rear left, it absorbs and rebound smoothly. Before the lower arm bush change, the noise was as if absorber was bottoming out (like its hitting top absorber mount) on almost every single bump. Absorber seems to be working fine by carrying out the bounce test though. Bump stopper is present too.

It could be the other bush on suspension assembly are worn out. For me, its definitely only on the right side. Tested by driving over same raised manhole (the ones where its slightly higher than road surface) on left and then right tyres. If you're around PJ, you could try the backroad from LDP turnoff to Mutiara Damansara heading towards Ikea. There's three consecutive slightly raised manholes and its on the way to Proton COE.

Have yet to send back for 2nd rectification. Will want to insist mechanic drive over the same road for them to understand the issue.