Here's the short scoop. The wife's '04 Corolla LE (auto) has been having some eratic idling issues at start-up the past few months, as well as a decrease in fuel mileage. I don't think the fuel mileage decrease has anything to do with "winter blend" gas as it was happening late in the summer. Back in October, I put in new plugs, air filter, transmission fluid, PCV valve, and oil change. The mileage didn't get any better after these changes. We're seeing low-mid 20's in town, and it typically would get in the low 30's, although I haven't checked it in the past couple of years since it's not my primary vehicle. I've got about 36psi in the tires, so I know it's not a low tire issue (in regards to the fuel mileage).
Last month I cleaned up the MAF, thinking it was dirty, but that hasn't helped. With the idle, it seems to want to "hunt" for its idle. Once it's idled for about 10 minutes and is off fast idle, it seems to be OK. Today in 14 degree weather, I started it and we were off after about 3-4 minutes. It had a noticible miss, so I brought it back home and took my Civic. Upon returning 4 hours later, I fired it up again, let it idle for about 8 minutes, and took it on a 4 mile trip. No problems and no missing.
OK fellow Corolla/Matrix/Vibe owners, have you experienced any of these symptoms? It's not showing a CEL, but it did a month or so ago. When we took it in, the dealer said it was showing a code because the ECU need to be recalibrated. They didn't say anything else was up with it. They said the code was more of a phantom code, as it wasn't doing anything to affect the performance of the car.
Might this be the IAC valve? I've read the thermostat can cause problems like this, but since the heater seems to be working as it should, I'd tend to think it's not sticking open. Any suggestions??
I'm going to keep an eye on it though.
