This car has been amazing since I bought it but I just hit 200k miles and as I went to the gas station last night when returning home in the driveway car in park the idle seemed to be loping like it was a v8 muscle car of some sort. Single mom with three kids and looking for a job... lol. I can not afford to try part after part until I find solution. What is the first thing you would look at and/replace?

P.s. I do all my own work on my cars so im not too uneducated.. PLEASE HELP ME!

 

Would coil and spark plugs be the first thing to change? Do I have to change both or can I just change one or the other? Looking at the engine do the coil packs go in order left to right 1, 2, 3, 4, 5, 6, ???

 

regarding coils - they are individual units so a more common sign of a failure would be a misfire code for that particular cylinder. #1 cylinder is up by the timing belt and count down from there. As to plugs - if they haven't been changed in a while, you could do that as a maintenance item. More likely cause for a loping idle is fuel trim - and the loping is the ECU trying to adjust. I'd start by checking for intake air leaks, scan for any stored fault codes, then check for fuel pressure. My list of possible causes would include intake air leak (vacuum lines, intake tubing, engine coolant temp sensor, fuel pressure sensor, ETM (electronic throttle body contacts), MAF sensor) which says a few more tests are in order before buying $400 worth of plugs and coils. Easy DIY for air leaks includes spraying around gaskets and injector seals and intake air tubing/boots with some flamable carb or MAF cleaner and inspecting vacuum hoses. You can also use MAF cleaner to clean the maf and throttle body (possible the the PCV oil separator needs replacing and has let some oil residue into the intake. After that you can measure fuel pressure and monitor run time fuel trim data from a scan tool. My approach would be to start with the simple tests you can do for yourself to rule out the easy/obvious that don't require guessing about what parts to replace. After that, you may need to enlist a shop to run some deeper diagnostics on the various devices as noted.