Wanted to go camping last weekend, but my 95 SR could barely go 65 on the freeway pulling a small trailer. Unsteady idle, bogging pedal response on acceleration, slow downshifts from the trans and truly nasty fuel consumption. In a headwind, I was revving near redline just to keep it above 60 (by comparison, last fall we drove over a bunch of 10,000 foot passes, barely noticed the trailer and averaged 14 mpg).

I changed the plugs (couple oil fouled, not bad). Checked the plug wires, checked all the coils (one coil had a crack in it and replaced it). Cleaned the throttle body. Sprayed carb cleaner down the PCV. Checked the air filter. Nothing helped.

Pulled the front 02 sensor and drove it around to see if the cat was clogged (doesn't seem to be running hot or backfiring, however). No difference.

It's not throwing any codes, no vaccuum leaks I've been able to find. It sounds like a sensor problem (MAF? CPS? 02?), but I can't believe it could be this off without sending a code.

I'm going to drop the cat tonight to see if the 02 hole wasn't enough to make a difference. And I'll go through the sensors with some dielectric grease to see if anything's loose, but what else can I check?

Thanks

How many miles on the motor?

Sounds like it's been crosswired. Check the order of your plug wires.

Not crosswired -- checked both before and after I did the plugs.

It has 175K -- haven't done the valve stem seals, so it blows oil during stop and go, but not bad enough for me to fix it yet. Haven't done the lower plenum intake either -- it's never made noise (I had it unplugged for the last couple of years, though).

Apparently not the cat either. I pulled it and could see through pretty well, drove the truck around without it and made a bunch of noise, but didn't go any faster. With the cat out, it did send a rear 02 code, not surprisingly, so I guess that means that sensor is working.

Put dielectric grease on every connection I could find. It might have done something -- it's hard to tell without the added weight of the trailer, but I was feeling like an idiot driving up and down my street pulling the trailer around all night. I'll try it tomorrow -- it'd be hilarious if a 50-cent packet of grease did more good than $200 in parts and hours of labor.

I dunno what else... some mice built a little condo on top of the plenum over the winter (had it parked for a month or so)... but I can't find any chewed wires or other mousy problems.

I got all weekend to lick this, so if you have ideas, keep 'em coming.

Andy

Would you get a compression test? That would let us know if it is something in the engine. If timing is right, you are getting good spark and fuel plus good compression, it will be something simple.

The one thing that stands out on your symptoms, is that the engine is close to redline while you are only travling at 60 mph. Assuming that you were in high gear or overdrive, i would think that your transmission is slipping.
Conner

This had me scratching my head last night: I was cleaning out the EGR valve (which was all coked up) and I noticed that if I pulled the vacuum line to the valve, the idle immediately smoothed out. It's not the valve itself -- if I plug the disconnected vacuum line, it gets rough again. And leaving the egr disconnected doesn't seem to affect the acceleration, but I can't see why pulling the line helps.

Regarding the transmission, it occurred to me, but I was pulling a trailer into a 50 mph headwind, so that's probably a bigger factor. It doesn't feel like it's slipping otherwise.

There should not be any vacuum to the EGR at idle.

For posterity's sake: It ended up being a bad plug boot on the No. 1 wire. Thanks for the suggestions.

For those of us who are always trying to squirrel these little tidbits away... how did you diagnose the problem and determine it was the plug boot?

Thanks!
Eric W.