9 MPG. Time for new plugs/coils?

[IslandCruiser808]

My 99 LC with 288,209 miles is getting bad gas mileage, about 9 mpg. Plugs and coils haven’t been replaced since owning it so I’m sure it’s time. My question is will this help me with my mileage, and is there anything else that could be done to help. Lots of stop/go driving in town while running the ac. Had the timing/water pump replaced about 2500 miles ago. Ran the OBD scan on it and no codes showing. Any help is appreciated.

 

[TexLexican]

Start with changing the pcv valve, clean the mass air flow sensor and throttle body, and change plugs.

 

[IslandCruiser808]

Start with changing the pcv valve, clean the mass air flow sensor and throttle body, and change plugs.

Changed the pcv valve out when the timing was done. Just cleaned the maf sensor last time I filled up gas and put in a fuel system cleaner additive with the gas. I have the new Denso TT plugs waiting for installation,but was thinking about getting new coils before I do the plugs. That way if get into the work I won’t have to wait for parts. I live in Hawaii and the dealership doesn’t do sales events and prices are a joke so having to ship most things here.

 

[BullElk]

I say you need the SK20R11 Iridium plugs. Also, you are likely to pay $700 for eight OEM coil packs and unlikely to do any good if your current packs are firing properly.

 

[76lcmike]

check your brakes, make sure calipers are not seized causing drag.....
check fuel trim see if it is running rich or lean,,,,,

 

[shane431]

Change your fuel filter. Cheap and easy.

 

[Camotubebender]

air filter too

 

[Trunk Monkey]

Has it always gotten about that fuel economy or did it get worse recently? If recent, something you changed that may have contributed?

 

[GTV]

As a rule of thumb it’s good practice to replace plugs at the same time as the timing belt since their recommended service intervals are similar. Inspect the coils at the same time, although a visual inspection won’t tell you everything. They’re usually good for 200-250k miles. I picked up genuine Denso coils from rockauto.com for about $50 each a couple years ago. Watch out for to good to be true fakes.

 

[IslandCruiser808]

I say you need the SK20R11 Iridium plugs. Also, you are likely to pay $700 for eight OEM coil packs and unlikely to do any good if your current packs are firing properly.

I picked up the Denso IK20TT Iridium plugs. I haven’t checked the condition of the coil packs but think I should get one of the boot kits just in case any of the boots need replacing.

Has it always gotten about that fuel economy or did it get worse recently? If recent, something you changed that may have contributed?

I moved from a rural area into town, so much more stop and go driving. It has been gradually getting worse, I run the ac much more also,not sure if that would affect the mileage much. I will try and check everything out that everyone has mentioned, and will be replacing the plugs in a couple days or so. Thanks again for the reply.

As a rule of thumb it’s good practice to replace plugs at the same time as the timing belt since their recommended service intervals are similar. Inspect the coils at the same time, although a visual inspection won’t tell you everything. They’re usually good for 200-250k miles. I picked up genuine Denso coils from rockauto.com for about $50 each a couple years ago. Watch out for to good to be true fakes.

I was looking at rock auto earlier today and they are around $51 or so.

 

[ceylonfj40nut]

Check that your cats are good as well

 

[Live to Ski]

9mpg stop/go sounds right. that's a lot of weight you need to accelerate.

take a long hwy trip using cruise control and report back with mpg.

 

[Octous]

One thing that hasn't been mentioned. If your fan clutch is seized this could cause a drastic reduction in MPG. Check to see if it's free spinning while the engine is off. While this won't tell you if your fan clutch is healthy, if it's seized it will be obvious.