So I have a 07 Scion tC. Bought it with bad exhaust valves and ran decent with them bent. So i put it in a shop and paid 4 grand for them to fix it. Get the car out of the shop and it runs very rough at idle with all the power it needs when i hit the gas. It idled perfect before putting it in the shop. I have changed spark plugs, coil packs, alternator, connectors, and even cleaned the MAF sensor since it could be dirty from a CAI and checked voltages of everything that would cause a rough idle. Its starting to annoy the hell out of me now and I don't want to put anything of the other parts i got for it till i fix the issue. It does occasional throw missfire codes for all Cyl but I don't know what else to do to fix this issue.

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I'm chasing ghosts too with my 2010 tC. Alternator kicked it so I replaced that and ever since then I've been chasing problems. Cleaned the throttle body and replaced spark plugs. I've got no CEL and haven't had a misfire since I had the plugs changed. I live in Hawaii and dont have a place to start taking my car apart and doing repairs myself so I have to be very specific when I take it in to a mechanic. I've got an engine mount that's starting to go "soft" according to my mechanic. I dont hear any hissing or whistling when my car is running but whenever idle it gets close to stalling and then revs back up. Problem appears more frequent when I'm delivering food with frequent starts and stops. Problem is also exasperated when running my AC or just my fan without AC on. I've tried relearning my idle as well as recently filling my tank and adding fuel injector cleaner. This is a problem that I know is going to get worse and I'm running out of things to look for. Hopefully adding my issue to this thread will get people to look at it again. Unsure if OP has gotten any feedback yet.