GorgeRunner

1990 standard pickup, 2WD with about 160K. Starts and runs OK but only gets about 20mpg, usually gets about 28mpg. The throttle was sticky, of course it was a little gunked up so I cleaned it out. This seems to happen about every 50K miles. I replaced the air filter. It had a tuneup a few thousand miles ago and the plugs looked fine.

I'm wondering if the dirty throttle body and air filter can be worth 8mpg? I'll see how it goes, but anything else I might want to look at if the mileage doesn't shape up?

osv

those trucks were rated at 20 mpg average: https://www.fueleconomy.gov/feg/noframes/7113.shtml

have you checked the odometer? the timing?

an1176

Tps and look for vacuum leaks.

an1176

Check for codes also.

GorgeRunner

I've always gotten close to 28mpg since the day I bought it. It's the base pickup with a 4 speed, some of the extended cabs and auto trans models got less gas mileage. I just tuned it up and set the timing a couple months ago.

Checking for vacuum leaks is probably a good idea, the rubber hoses on the engine are old. I hesitate to mess with the TPS because the truck runs fine(for being 26 years old with the original engine) and the timing is easy to set and stays where it is. This truck uses the older code readers, I usually wait until the engine check light comes on and read the flashing light codes on the dashboard. Only one engine check light so far, an O2 sensor in the exhaust pipe.

Well, this morning the engine started to surge at idle when I got off the freeway. It only lasted a few seconds and went away but the idle still seems high so something is going on besides a dirty throttle body.

an1176

Easy way to check tps is to get engine to operating temp them jump the te1 e1 relay. If it idles down probably not tps. You can have codes stored that don't show up. Again jump te1 and e1 to check for codes. When did you have o2 code? That'll affect mileage. I had a worn out rubber elbow that goes into throttle body. Visibly you couldn't see any leaks. I put a smoke leak detector to it and I had about 1000 small pen holes in the elbow. Also my cold start injector was leaking vacuum. Google and look on forums for surging idle. There are lots of issues that'll cause that. Too many to start listing. Does it smell rich when running like gas? Good luck.

GorgeRunner

Yes, I checked the numerous and widely varied reasons for poor gas mileage. I had a couple instances of surging idle after freeway driving that just cropped up as well. I checked for vacuum leaks and cleaned a couple sensor connections and I plan to check the codes. I think I may have messed up the TPS when I cleaned the throttle body, perhaps the reason for the surging idle, but finding the cause of the poor mileage may be a little tougher.

an1176

I had slowly developing poor mpg. I have a 22re 4x4 went from 18 to 19 to 15 over time. Mine ended up being several issues. Vacuum leaks at cold start injector and rubber elbow. Exhaust leak at manifold and before o2 sensor. I'm back to 18 mpg. Vacuum will cause a lot more issues then exhaust. Mine smelled rich too (burning to much gas). That's a symptom of vacuum leak. Honestly it could be many things. Do a lot of trubble shooting and research before you start throwing parts at it. If you know anyone with smoke leak detector they work wonders in helping find vacuum leaks and exhaust. Another trick I used was to take my shop vac and attach to the intake very loosely so a lot of air can escape open your throttle all the way then get a soapy spray bottle and spray everything that has a vacuum hose or gasket that has to do with intake. I did the same think with exhaust. I was amazed at how many leaks I had. Good luck.

GorgeRunner

This is the kind of problem where you wish something would actually fail completely so you can fix it. It's an old truck, stuff just wears out.

GorgeRunner

I think I may have solved, at least, part of the problem, here's what I did should anyone be searching "22re poor gas mileage" or "22re idle surge" in the future.

The crankcase breather hose in the very front of the engine had a crack in it, but the crack was facing towards the rear of the truck so you couldn't see it. I took the hose off to clean it and run a wire through the tube into the throttle body. This hose for my 1990 22RE is not widely available and costs $25, so I wrapped the hose tightly with electrical tape. Even the cheapo stock wire hose clamp holds it tightly to the valve cover. No doubt this was causing a vacuum leak.

The idle screw and seat in the throttle body was caked with black carbon deposits. I wire brushed and used scotchbrite on the idle screw to clean it up and used a small screwdriver to scrape the deposits off the screw seat and used wooden stick cotton swabs and alcohol to clean it up. A bit of silicone grease on the idle screw O ring.

These two things were right up front and a good place to start troubleshooting.

This is probably not typical, but there is an air injection manifold or tube, whatever you call it, above the exhaust manifold and under the heat shield that had a small hole where the tubing was welded together, causing a leak. I stuffed a piece of tin foil in the hole and sealed it up with JB Weld. I don't know if this will hold or not, but it's all I've got right now. I'll keep an eye out for something better.

It seems a simple fix now, but when you start looking for a vacuum leak with all the hoses on a 22RE, it seems impossible.

an1176

Cool. Good job. Is it running better?

GorgeRunner

Seems like it. Give it a few days for the ECU to readjust. Thanks for your input.