Poor Fuel Mileage - Toyota Nation Forum : Toyota Car and Truck Forums

jmr1000 · 09-17-2009, 06:31 PM

Hi all! New to the forums and seeking help.

So, here's my issue...I have a 98 camry (calif emissions, 173,000 mostly freeway miles) and for the last year I have noticed that the fuel mileage has been getting progressively worse (down 6+ mpg). It has not thrown a cel, but I'm wondering if one or more of the air/fuel sensors have gone bad, and possibly the cat. I have also noticed that the exhaust smells bad. The car still runs good, maybe slightly less power and a little rougher, but nothing extreme.

Since there is no cel, could it be that the sensors have not totally failed, but have just gotten lazy? Also, could it still throw a code w/o a cel? I'm wondering if I should take down to autozone for a scan. If I knew it was the sensors for sure I would just replace them, but I don't want to go and start throwing $ at the issue. On the other hand, I've been told that the sensors usually have a 100,000 life span.

A little maintenance history... been using synthetic oil for the last 90k, 50k on fuel filter/plugs/wires, 15k on air, recent TB cleaning, no extra weight in car, tires properly inflated and I throw in a bottle of FI cleaner about twice a year.

Thanks in advance for your help!

Jason

Retrospekt · 09-17-2009, 07:19 PM

Depending on what spark plugs you use, the ones in there could be 20k over they're due replacement mileage.

Buy a can of SeaFoam and put 1/3 in the brake booster line, 1/3 in the oil, and 1/3 in the gas tank. Drive it for 50-100 miles or so, then do an oil change. Leaving the SeaFoam in the oil for too long can cause oil leaks on high mileage engines, so it's recommended you change the oil.

jmr1000 · 09-18-2009, 01:30 AM

Thanks for the response Retrospekt.

The camry currently has the oem denso plugs. The last set went 70k before I changed them, even though they were still good. Just to be sure, I checked them yesterday and they look good. Light brown, so I know things are running good. So, you don't suspect the a/f sensors, even though they are the originals?

I will give the seafoam a try. Which parts stores carry it?

Thanks again!

chick.with.a.wrench · 09-26-2009, 01:37 AM

Also, make sure that if you have the ECT and O/D buttons that they are both off (no extra dash lights on). I was having that same problem with my 93 and i turned all that crap off and changed the oil and spark plugs and now everything is perfect.

And almost any parts store should carry SeaFoam.

Camry LE 94 · 09-27-2009, 10:39 AM

You can get Seafoam at Auto Zone/Advanced Auto... Make sure you get the regular kind as there's a type called Seafoam Deep Creep (for cleaning your TB and is safe for the IAC valve), and Seafoam for transmissions.

chick.with.a.wrench is right, however. You should only have the O/D off (light on dash) when you're consistently going under 40 mph, such as city driving. if you don't have it off during this type of driving, your tranny fluid will eventually burn up quicker and will need to be replaced asap.

dave986 · 09-27-2009, 01:54 PM

advance auto parts is 7.99 for a bottle, great deal

carsrus · 09-27-2009, 05:44 PM

Is your exhaust/muffler good? A leaking exhaust and bad muffler can affect it too. I would change the o2 sensors since at 170k there way over due. The sensors might be almost bad or just sending a bad signal to the computer.

jmr1000 · 09-30-2009, 12:05 AM

Thanks for all the replies. I always use O/D and just tried seafoam through the brake booster. It seemed to smooth the idle, but I'm not seeing an improvement in mileage, but then again, I haven't even put a tank of gas through it yet. I'll check the exhaust and muffler.

Next question, if a sensor or sensons were bad, wouldn't it run either rich or lean? I ask because the plugs don't show any signs of running either rich or lean.

I'm thinking the next steps are plugs, fuel filter and then sensors, but welcome all suggestions.

Thx again!

chick.with.a.wrench · 10-02-2009, 01:29 AM

I would do exactly what you think you should do... In that order. Plugs, fuel filter and then if it still persists, sensors.

Idk If you knew this or not... just throwing it out there, if your plugs are bad... they are either going to be full of oil or BONE dry and the tips of them are going to be kind of charred and almost rusty looking. If your plugs are oily, you have a bigger problem, if they are bone dry they are good but if there's also charring and rust-looking "build-up" or it just looks rusty, replace them.

Also check your plug wires to make sure they are still in working condition but I think you are spot on in the steps you should take to try and fix your problem.

jmr1000 · 10-02-2009, 01:26 PM

Thx for the insight on the plugs chick.with.a.wrench. The plugs are the oem denso 3253 DP and the plugs/wires have 54,000 miles on them. They look good with no rust coloration. I would have thought that these plugs would have lasted longer since they are double plat, but I will change them out along with the fuel filter and see if that makes a difference.