noise/RPM change going uphill
Hello from a recent member. I have been lurking and getting ideas, but now I've got an issue I could use a hand with.
I can't afford to have somebody competent look at this, so I figure I'll give it a shot. The problem is this: when I go up slight hills and maintain speed, anwhere from say 40-60 mph, I get this hesitation. There is a faint tunk, followed by a vaahroom, and this is repeated perhaps 2 times every second. I feel the car stutter when this happens. Gas mileage has been horrible since I got the car. That was three years ago at about 106k. I get about 250 miles per tank. Worse lately. I have a lead foot, but I wouldn't have thought it would be this bad. I don't throw any lights. I hope it isn't the tranny. Edit: Is this that stupid surging thing that others have mentioned?
I have already tried fuel injector cleaner. I did my plugs maybe 10,000 miles ago with splitfire plugs from Wal-mart. They had never been done I don't believe. They look pretty much normal for wear as far as I can tell. No black gunk or anything.
I didn't do the wires at that time. I did the PCV valve a few thoursand miles ago. I just did the air filter. Did the fuel filter when I bought the car (18k miles ago), I do my oil changes every 3,000 miles. I drive 1 mile back and forth to work, plus stop and go driving rarely over 15 minutes. I drive for 1.5 hrs on the highway each way perhaps twice a month when I go up to the twin cities.
The ignition coils are also original. I took them off and cleaned the corrosion off the plate, but that didn't help. I have not checked them with a meter yet, as I just discoered that on the site today. Is this worth checking?
Basically, I intend to do the following over the next few months as money allows (I'm a broke medical student). I will do new plugs and wires, the oxygen sensor, may do a new fuel filter, The question is, where do I start? I was thinking the first step is definitely to check the ignition coils, because that is free to do. Next, I would probably do the oxygen sensor.just because my mileage has been so bad, and I wonder if that might be causing this problem as well(getting a little rich?)..
I'd appreciate any insight into what might be going on and cheap ways to assess it.