2004 Corolla idling & fuel mileage issues....

[Pat in Speedway]

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??

 

[mechtech2]

This could be SO many things!
Your coolant sensor and air temp sensor that feed the computer with information may be out of range, or otherwise whacked.
How about the O2 sensor [the first primary one is critical].
A miss can also be basic things like plug wires or coils, or injector flow problems.
A good cleaner run through one tank of fuel will help in any event.
[Gumout REGANE, Chevron injector/valve cleaner, Redline S1].

 

[mikered30]

Look up US version TSB EG022-07. It covered under 96 month/80,000 mile emissions warranty in the US. Its description says that it corrects "hunting idle" after start in cold weather but for manual transmissions, but you have an auto. See http://www.9thgencorolla.com/forum/showthread.php?t=69562&highlight=idle for more info. A copy of the TSB is on that site, but it is the Canadian version of the TSB. Maybe you can talk to the dealer to see if the TSB was expanded to cover automatics?

 

[jamesn]

you probably need an idle air control valve. they commonly go out on these engines. not terribly cheap but you can install it yourself.

 

[mikered30]

Here is how to clean your TB and IAC valve: http://matrixowners.com/index.php?showtopic=65513

 

[Pat in Speedway]

Originally Posted By: mechtech2
This could be SO many things!
Your coolant sensor and air temp sensor that feed the computer with information may be out of range, or otherwise whacked.
How about the O2 sensor [the first primary one is critical].
A miss can also be basic things like plug wires or coils, or injector flow problems.
A good cleaner run through one tank of fuel will help in any event.
[Gumout REGANE, Chevron injector/valve cleaner, Redline S1].

Shouldn't the sensors be triggering a CEL event? It's not been doing that, aside for last month when the recalibration issue popped up. I've not noticed the miss before and she hadn't either. There might've been a few factors at play there...it was 14 degrees, and the car wasn't sufficiently warmed up, although I don't think cold weather should make a big difference, as doesn't the computer make the necessary adjustments for temps?

I'm going to keep an eye on it though.

 

[Pat in Speedway]

Originally Posted By: mikered30
Look up US version TSB EG022-07. It covered under 96 month/80,000 mile emissions warranty in the US. Its description says that it corrects "hunting idle" after start in cold weather but for manual transmissions, but you have an auto. See http://www.9thgencorolla.com/forum/showthread.php?t=69562&highlight=idle for more info. A copy of the TSB is on that site, but it is the Canadian version of the TSB. Maybe you can talk to the dealer to see if the TSB was expanded to cover automatics?


Thanks Mike....I was reading up on it last night. I've got a hunch it's something that cleaning or replacing the IAC valve won't cure. I thought it was odd the bulletins are geared for manual transmissions, but mine seems to have the same symptoms. I just hate throwing money away "guessing" it might be this sensor or that one. From what I read, it looks like they've added data to the ECM to make the adjustment, as opposed to just recalibrating the ECM, which doesn't make the problem go away, apparently. If we decide to take it in, I might drop it off the night before & let them fire it up on a cold morning so they can see first hand. Thanks for the reply!

 

[mikered30]

Originally Posted By: Pat in Speedway
Originally Posted By: mikered30
Look up US version TSB EG022-07. It covered under 96 month/80,000 mile emissions warranty in the US. Its description says that it corrects "hunting idle" after start in cold weather but for manual transmissions, but you have an auto. See http://www.9thgencorolla.com/forum/showthread.php?t=69562&highlight=idle for more info. A copy of the TSB is on that site, but it is the Canadian version of the TSB. Maybe you can talk to the dealer to see if the TSB was expanded to cover automatics?


Thanks Mike....I was reading up on it last night. I've got a hunch it's something that cleaning or replacing the IAC valve won't cure. I thought it was odd the bulletins are geared for manual transmissions, but mine seems to have the same symptoms. I just hate throwing money away "guessing" it might be this sensor or that one. From what I read, it looks like they've added data to the ECM to make the adjustment, as opposed to just recalibrating the ECM, which doesn't make the problem go away, apparently. If we decide to take it in, I might drop it off the night before & let them fire it up on a cold morning so they can see first hand. Thanks for the reply!

No problem, I am not sure either why it applies to manual transmissions only.

 

[jamesn]

i checked and the IACV will not trigger a check engine light if it is going out. once it stops working altogether it should trigger one. i would recommend berrymans b12 chemtool from the aerosol can. if it is stuck that should fix it.

 

[mechtech2]

Sensors may or may not trigger a CEL.
It depends on how out of range they are.

 

[mikeg5]

first off. what kind of plugs and etc did you use?? hopefully you used denso or ngk.. if not thats where i would start. some yotas are picky with what you put in them. plus do a seafoam treatment