04 Corolla - idle & gas milage

[koltrayne]

Hi Folks - new member.

I bought an '04 Corolla in '06 that had a somewhat bad idle that has gotten worse "sometimes" over the years. It was previously used in dusty environments - construction guy owned it.

I started monitoring the gas mileage - found it was about 24 - and tuned it up, replaced ignition wires, plugs (not iridium), etc. The mileage improved slightly over time.

Then I cleaned the MAF (reading about it here), put injection cleaner in at each fill up and put a new air cleaner in. Over the next 2-3 fill ups the mileage went to 34 and the idle smoothed out. Great!

But the cycle began to repeat itself over subsequent fill ups - like a sine wave - 24-33. But now it's stuck in the low 20's even though I do the same things as before- I don't even want to calculate it now. The idle roughness is back.

An O2 sensor? Gasket?

(I haven't done the throttle cleaning yet.)

I'm thinking I now need an "expert" to look at it with diagnostics. The local dealership is my last resort - not sure I trust them.

Any advice, war stories relating to this?


Thanks in advance.

[mikered30]

Does the idle roughness and poor mileage occur only in the winter? How does your tach respond on cold startup?

[koltrayne]

That's interesting. I haven't paid attention to winter/summer but I would say offhand since it's bad right now and has been real bad for 3-4 months - yeah it probably is worse in cold weather.

What should I look for on the tach when starting up in cold weather?

It seems to idle high on first starting these cold mornings then settle down to maybe 700-800 RPM at temperature.