Well the infamous "I seem to always get 18-20 mpg, even lifted" statement has finally caught up with me.

The last few fill-ups have been around 14-16 mpg. I'd have to look at records, but last oil change (I'm about due) I replaced the fuel filter. Aside from that I haven't changed a thing to the vehicle. Up until about 1 month ago I was still getting my 18-20mpg combined city and highway. Checked tire pressure, checked air filter (dirty, but not bad), spark plugs were changed back around 50K (at 61K now). And checked the IAC per recommendation by Haynes/Chiltons manuals. RPMs cut upon pulling wire, resulting in the engine stalling.

RPMs have been higher than normal upon initial crank. She's been holding around 2500 for longer than I'm remembering before kicking down to 1100 to 800/900.

So things that are running through my head are:

-inspect/replace PCV valve
-clean MAF (I know there's a how-to on this somewhere!...)
-fuel injector cleaner next fill-up
-bad fuel filter
-winter fuel blend (I noticed a drop in mileage last year, but my suspension was also stock at the time).

I just went and purchased oil, oil filter, fuel filter, PCV valve, air filter. I'm particularly interested in the PCV valve. I've nenver replaced one, let alone messed with it, so how does one go about cleaning the hoses if my PCV is indeed clogged (no rattle when shaken)? I found Bob's how-to on replacing it, but no mentioning of cleaning the hoses.

 

Check your wheel bearings. I just changed one and got 1 mpg back.

 

That high of an idle when cold tells me either its a vacuum leak or a sticky IAC, or a sticky throttle plate/bore.

As far as milage.. usually a bad 02 causes that. Could also be low tire pressure or a dragging brake maybe? Or.. maybe your area has switched over to winter gas? (that always effects us in the north)

Rich

 

to check a PCV valve, shake it....if it rattles, then it is still good...

 

I forgot to mention O2 sensors.

That was my other thought. The drop was similar to what my 93 did when it's O2s went, but that also threw a CEL. I haven't gotten a CEL yet, but I also know I might not get one either; at least for a little while. I haven't had a chance to peek under the truck, but going off memory I can only picture 4 O2 sensors. I seem to remember reading 2 per cam head, or something alone that line?

I definitely think something is up with the IAC, even though it performed how Haynes/Chiltons said it would for testing. I hope I don't have a vac leak or issues with throttle plate. The 2500 quote is off. She sticks at 2000 for about 20-35 seconds - sometimes longer, drops to 1300-1500 and holds, then drops to about 1100. Once moving and then stopped she'll idle at 700-800.

That'll be the first thing I do after the oil change.

 

Inspected those in July when I put the RCD kit on. I was set to replace them if needed, but they appeared fine according to the guy that was helping me with the kit.

 

Plan on them lasting about 100k.
My first one was toast at about 113, second one at 122.

I put on 265 rubber at 22k so that may play a role in bearing life.

 

Does the throttle fell sticky when first pushing it? Your idle sounds like it's just a little on the high side. And the idle coming down sounds like the IAC is working properly.

Sometimes a ridge of carbon builds up on the throttle body right where the plate touches it. Clean that ridge off with "throttle body cleaner" Its in a can and looks idectical to the "carb cleaner" but it's specific to throttle bodies that have a protective coating. (carb cleaner can hurt it)

While you have the cleaner in your hand.. take the PCV off and spray cleaner into it. Both ends and shake/spray it till clean fluid runs out.

See if that effects you idle speeds.

You'll have either 2, 3, or 4 O2 sensors. Two are in the exhaust pipe just ahead of the first cats. Then you'll have either 1 or two after the last cats (depending on yr)

Rich