BR549

I have a 1985 Toyota Pickup, 55k miles (yes, only 55k), manual, 22R engine that has suddenly begun running very rough at idle, and at all RPMs too. It started the first time while driving at less than 30 mph and with the engine still warming up. Begun sputtering and wanting to stall when foot off accelerator. Hobbled back home, blew a lot of dust (that looked like remnants of a wasp's or dirt dabber's nest) out of the air filter, and it ran fine all the way on a 50 mile or so errand. A few days later (with gas tank nearly empty from that previous long trip), started up and immediately ran rough all the way to gas station, wanting to stall again if foot off gas. After filling up, ran fine all the way back home. Since then however, it has been running rough right from the start. Spark plugs are covered in dry black soot, indicating running way too rich (?). Plugs only have 10K miles on them. Clean 'em up, starts and seems to run smooth for a few seconds, then back to sputtering and very rough. Choke and carb spray hasn't fixed it (limit of my carb repair ability). Choke seems to work as it should. Thinking it might be emission control related or ignition related as reason for overly rich mixture, have checked as many things as my limited mechanical knowledge allow, such as PCV valve, EGR valve, EGR Vacuum Modulator, HAI, MC Valve, Spark Plug wires, timing, igintion coil resistance. Did replace PCV grommet, as old one had crumbled. Fished out bottom part of grommet from top of flame arrestor (?) During some diagnostic procedures, have heard afterfire or explosions while accelerating or decelerating. Yesterday while wife was revving engine so I could take short video to share with a friend, I heard exhaust sounds coming from muffler and looked under truck to see many rusted out spots. Which leads me to my latest theory and question: could a bad muffler be the root cause? If muffler is rusted out inside, and creating too much backpressure, could that be affecting the amount of vacuum and tricking the EGR system into delivering too much exhaust for re-combustion or otherwise affecting the gas/air mixture and giving me symptoms of running too rich? I dread the thought that it might need a carb overhaul, unless somebody knows of a good mechanic in the Houston/Galveston area that they would trust to do the job. Any and all suggestions, or where else to look or what else to try welcome! I need my truck back ... wife doesn't like me haul wood, tools, ladders, etc. in her Prius!

jimbyjimb

iTrader: (1)

An exhaust restriction can certainly cause problems, but with the level of deterioration you describe I would suspect that the exhaust would just blow out if there were any bad restrictions. Maybe not. You can always unhook the pipe from the manifold and run it, see if that helps.

If you're running rich the problem can be in the fuel system, probably the carb. Could be an internal failure, bad settings or the choke. I am not intimately familiar with stock carbs; I just chuck 'em for a Weber/Holley.

EGR's can certainly affect idle if/when they get stuck open. You can remove and inspect the EGR, make sure it is closed and check the diaphragm for operation. Or, if you're smart, you'll just put a threaded plug with some thread-tape into the EGR port on the head after you remove the valve and eliminate it all together. Pieces of junk.

I would start with the EGR as it's a simple two-bolt or nut removal and pretty easy to inspect or eliminate. Do yourself a favor and eliminate it!

BR549

UPDATE/PROBLEM SOLVED:
First, thanks to jimbyjimb for his ideas and suggestions. While I agree the emissions system is a lot of tinkering to make something run better, I'd rather not start removing whole pieces, at least not yet. After replacing the muffler (it needed it) and being told the catalytic converter was OK (an honest muffler tech if there ever was one!), I bit the bullet and went to Toyota dealership for a diagnosis. While it was stuttering and puffing when I pulled in, of course it ran fine when the technicians looked at it and drove it. Determined to find something, I was told I needed a new clutch! Dismayed, I got the technician to take another test drive, and I got to ride along. The patient ran fine ... whole going the doctor thing. BUT, in talking directly to the tech during the drive, I was able to pass on more of the symptoms than the service writer had included, and he thought it sounded like the Auxiliary Acceleration Pump (AAP) Diaphragm. When we concluded the test drive, he even took off the air cleaner to show me where it was and a way to troubleshoot it on my next cold start. The diaphragm was cracked, allowing fuel to enter the vacuum system and pumping way too much fuel into the carb. Between a lot of idling and revving while trying to diagnosis it myself and the trip to the muffler shop and the dealership, I used up 6.8 gallons of gas and only traveled 66 miles! As it turns out, once warmed up, the symptoms continued even though the BSVS was not calling more fuel, and it was stuck in this overly rich cycle. Once the engine was cut off and then restarted, and if it was still warm, it cleared the excess fuel and/or fuel in the vacuum system (usually by a hard start) and then it ran fine. So, my intermittent problem was really still there, it just only presented itself on a cold start. Three hard to reach screws, and investment in a ratcheting right angle screwdriver, a call and trip to NAPA Auto Parts for a new $15.95 AAP Diaphragm, and all is right with the world.

jimbyjimb

iTrader: (1)

Fantastic! Glad it was an easy fix.

coyote jim

If the problem rears it's weary head again while climbing a long hill or in the heat of summer, I would certainly look at a plugged cat converter. You have two choices, punch it out or buy a new one. A gas analyzer would quickly tell you if is the case.

Mr. No SPAM

I ran into this very issue on the California '82 2WD I bought not long ago, but the symptoms were a tad different. It would start OK dead cold, but would quickly develop a low, lumpy idle that was obviously rich. Could see it in the black exhaust too. I could drive it OK but it idled rough and would stall out, especially after the high idle cam backed off. But then as soon as it warmed up all the way, as if a switch was flipped, it would idle nicely and run that way all day long. The only time that poor idle would come back was if it had a chance to cool down enough.

I went through the book and checked a bunch of stuff to no avail. What finally nailed it for me was letting it idle cold and rough as it was, and pinching off vacuum lines at the source on the manifold until I found one that smoothed idle out.

When I pulled that line off at the source I found gas in it. I traced the line back through to the "TVSV", and then to the Aux. Accelerator Pump diaphragm, which was leaking gas into the vacuum system, especially while cold and the TVSV was open and allowing a path to the intake.

My immediate fix was to cap off the hose fittings between the AAP and TVSV, and this alone restored the ability to start the engine and drive when cold without any major headaches. I've since replaced the diaphragm and all is well.

I also noticed a significant increase in fuel economy after making the repair (17 - 23 in town). It seems there was still some gas getting sucked through the TVSV, even after it was warmed up and closed off.