Engine and hold lights flashing

[HeavyDuty]

Well if someone at a dealership did as you suggested I would never take my car to them...ever. The reason you pay high labor charges at a dealership in part is for EXPERIANCE and also in part for EQUIPMENT to test. Any one can throw parts at a problem in hopes of fixing it....but I would not call them a mechanic LOL

The person you want to be working on your car mechanic or not dealership or not is the guy you call up and say hey every time I start my Aveo it sets a P300 and he say's oh that's the X and you take it there and he puts X in and away you go problem fixed. This only comes from experience and logic.

Every single part can be tested in the hands of someone a) with the knowledge and b) the tool to test it...and last but not least even with previous two they still need to have some LOGIC.

These days that's VERY hard to find I am afraid, rapid changes in technology and a number of other factors play into this as well.

You are having a P300 code set ?

In my 2009 Chev Aveo owners manual there is a paragraph about the transmission not shifting does the 2005 manual have the same blurp ? A random miss fire could be caused by the WRONG plugs......or even a fuel injector, the driver can narrow it right down, if he has some mechanical knowledge....the little test drive mechanics "USE' to do was for this reason.

It seems in at least one of these cases the car is running fine but setting a code, if it tells you it has a misfire and there's no misfire....then whatever detects misfires is the problem...if a misfire is present and setting a code, well that's another ball of wax.

When a misfire occurs, engine speed will fluctuate. If the engine speed fluctuates enough to cause the Crankshaft Position (CKP) sensor signal to vary, the Engine Control Module (ECM) can determine that a misfire is occurring.

Does the throttlebody have anything to do with engine speed or possible engine speed fluctuations ? Indeed it does is that your problem, I can't say but am sure your TB could use cleaning anyways right (that's some logic).

If the mechanic told you the relearn wasn't the problem...take it somewhere else and have it done. Mechanics have this really bad habit of you can't possibly know anything....and may have dismissed it just because you suggested it and further they may not even know how to do it so of course THAT CANT BE THE PROBLEM.