I have gone from 20mpg to around 15mpg in town and from 25mpg to 20mpg on the highway. Looks like I need a tuneup but not sure what to get done and don't want the garage taking me for a ride. What would be the best things to start with since I am on a very tight budget.

 

I would look at the air filter and tire pressure first. How is the van running?

 

Avoid ever asking for a "tuneup". The days of points, cap, rotor, condensor, etc. are ancient history for passenger vehicles. A tuneup these days is often no more than new spark plugs and (maybe) ignition wires. Most shops are honest, and won't do unnecessary work. But there are a few guys who will hear you say tuneup, and know they can get away with doing next to nothing, and charge you a few hunderd bucks in the process. So always ask for specific things. In this case you would tell them the gas mileage has dropped significantly, and ask for a diagnosis and estimate for that alone. Request no work done prior to an estimate, and ask beforehand what, if anything they charge for the estimate. It's not unreasonable for a shop to charge for an estimate - some do, some don't.
That said, first do what MT already posted, because that's very low cost, and something you can do on your own. Next in line would be spark plugs - do you know when they were changed last, and what kind were installed?

 

Winter gas and cold winter temperatures will increase fuel usage considerably. And the cold weather will lower the air pressure in your tires; so as the weather cools you need to check the air pressure more frequently.

If your engine is running well then don't expect much improvement from a tune-up.

Good luck.

 

I always say when someone gets a tune-up there is one key thing always missed, O2 Sensors! When i do a tune up this is the list that i do

Plugs & wires (Rotor and cap if the engine has it like my Jeep) Go OEM not no gimmick plugs! and i also recommend Autolite pro series wires
02 Sensors Also OEM here May cost more but will be loads better and they could also effect gas mileage!
Oil + filter I always use Rotella Oil.
Coolant flush and refill
Air filter
clean all connections i can get to
half can of seafoam in the gas tank
Half can of seafoam through the Vac line into the intake (I do this to all my cars when i first get them and then once a year after that) I never put it in the oil. And how i always do it is i pull the vac line off the brake booster and drip it into the line while running until its near the end of the can then i dump it in to stall the engine out and let it sit for about 20mins then i start it up and run it down the road and once the smoke clears so should any carbon build up in the engine, Note it would be real hard to start at first and will smoke like a frieght train for afew mins/miles. If you never done it before google it.

Also another note for gas mileage is loose the dead weight! If i remember right for every 100lbs you remove from a car your MPG will increase by 10% so always keep a clean car, keep a eye on tire pressure, Alignment, OEM tires, (Yes off brand/non OEM can effect handling, MPG, Ride!) Anything on the roof rack? Remove it!

Believe me this works! I also own a 1996 Jeep Grand Cherokee 4X4 5.2L V8 and i get 25mpg hwy, 17mpg city so its living proof.

 

airwolf9090 - I've never done a "tune up" on my 96 GC with 214K miles. I've changed the plugs twice if that counts. Still has original plug wires. Oil/filter get changed every 5K miles and I drained the coolant and tranny fluid twice. Air filter gets changed every other year and I live in a desert. That's about it. Odd thing is it has always run like a top with the same 18/24 MPGS it got when I drove it off the lot in 95.

wheelchairman36 - My first step would be to change the spark plugs taking note of their condition. Double plat Champions or Autolites work fine. Stay away from Bosch. The electrode should be undamaged and the business end should have a light grey or tan appearance. Dry black soot or oily wet appearance means trouble. http://www.ngksparkplugs.com/tech_su...qs/faqread.asp