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#1 Kathy

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Posted 05 February 2009 - 01:53 PM

My 2005 Toyota Corolla has 106,000 miles on it. I've changed the oil regularly and have never had any problems with the way the car runs until just recently. Lately, it's been idling a little rough. I've noticed when idling, it registers around .6 or .7 RPM on the tachometer. It seems to me the idle is set too low. I have tried fuel injector cleaner in two full tanks recently, but that didn't seem to help. I also changed the air filter. An old friend of my father's is going to change my spark plugs this weekend for me. (I understand I should get the iridium tipped ones.) He wanted me to get a new fuel filter to be on the safe side, but I just found out you can't replace the filter -- you have to replace the whole unit. My question is --- does anyone think my friend should check anything else out after he changes the spark plugs? I'm hoping that's all it is.

(I only know a little bit about cars from when I used to watch my ex work on them.)

Thanks.

Kathy

#2 fishexpo101

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Posted 05 February 2009 - 02:03 PM

Hello and Welcome to the Forums.

Given the mileage on the car and that fuel additives/air filter didn't do anything for you, I would recommend the following items to check out first.

- check sparkplugs and determine if they need to be replaced (verify plug gap is at 0.044")
- check and clean the MAF sensor / IAT assemply if necessary
- check that the throttle body is free of heavy carbon deposits, gum and varnish (these will form naturally over time)
- less likely, but possible - a faulty COP (Coil on Plug) igniter or ECM (Engine Control Module - the car's "computer")

I'd look into getting the spark plugs replaced (Toyota recommends 120K mile change interval - but like most things, your mileage my vary). I changed the plugs on both my cars before 120K mile mark - the Matrix actually started to misfire before it got that far. The Corolla faired a bit better - got about 95K miles before I decided to change them out. Also a good idea to note if any of the sparkplugs looks significantly different from the others, if that is the case - note the cylinder that the plug came out of. There is a small chance that there could be a faulty ECM or COP that is causing the poor idle.

Best to stick with the OEM Iridium sparkplugs (part numbers are in the Owner's manual or you can read them off the plugs themselves). You don't have to get them from the dealership - they can be found in many autoparts retailers and online.

Also look at doing a MAF/IAT sensor cleaning - I believe there are several posts in this forum on it. Not something that is normally considered a "maintenance" item - but many have reported significantly improved idle quality after cleaning the MAF sensor.

A throttle body cleaning is also another good idea. Carbon deposits and varnish can form inside the throttle body and can cause the throttle plate to stick and clog the air bleed hole in the TB (lets air in without opening the throttle plate at idle). Your throttlebody is a DBW (drive by wire) design - you should be very careful working on it, as if the unit is powered, there is a chance you could damage the servo on the side if you forcefully open the throttle plate. Also outlined in the forum as well.

I would probably avoid "injector cleaning services" that many places advertise. They charge an obscene amount of money for something that may not work for your case. Some cases, can actually cause problems with the injectors themselves or potentially damage this engine's returnless fuel system.

As for the fuel filter - it is inside the gas tank and part of the fuel pump assembly. There are two parts - the external "sock" that protects the pump and the fuel filter itself, wrapping around the fuel pump. Generally speaking - they should not need to be replaced under normal operating circumstances. Unless you have drivability issues at speed (car seems to be low on power, hesitation at speed, shaky idle, engine "misses" under load, etc.) - I would not suspect the filter. It has a "self-flushing" ability (due to the returnless fuel system design) and generally won't need replacement unless you filled up with diesel, leaded fuel, or known "dirty" or suspect quality unleaded gasoline.

Good Luck.