Picked up an '86 with a reman engine (supposedly ~60k ago) that has.. some issues. Namely, it runs awesome for the first 1-2 minutes of a cold startup, then it abruptly drops idle to less than 500, shakes like crazy, and dies (most of the time, sometimes it stays alive but sounds like it has a huge cam in it). Always fires right back up, but I basically have to heel-toe the throttle and brake to keep it alive when stopped. Does okay at speed, drove it ~70mph on the highway home and it was fine the whole time in every gear. Once I got it home, I started digging into it and found a few things. Could just use some input.

1) The adjustment screw on the AC/steering idle up valve was broken off, so there was a lot of suction there. Placing my finger on it didn't seem to change anything but the suction was strong so obviously it's pulling a lot of air. Replaced that with the one from my other basket case, but there was little to no change.
2) Throttle body shaft had some wiggle to it, and some chuckle˟˟˟˟ tried spraying it with something to seal it up (shiny and black, not sure). I know these can leak, so I replaced the whole TB with the one from my other truck, that had very little shaft play. This seemed to make it "roar to life" on a cold start, but it still dropped idle to almost nothing and can't be kept alive. Idle air screw had some effect while cold, able to idle from very low to very high, but I can't find a position that will make it idle warm. I can adjust the dash pot screws to mechanically raise the idle via the linkage position, so that it at least won't die (much like having my toe barely on the throttle), but I can tell it isn't running right. Lots of shake and sounds really lopey.
3) The vac switches on the valve cover are just not there. My other truck had two or three... BVSV, VSV, etc. I see one vac line is run straight to the FPR, which I've read works fine, but can you delete the others without issues?

I have not yet: removed the IAC and cleaned it out, or tried swapping it, I haven't tested/adjusted the TPS, though it looks like it's been replaced (OEM luckily), I haven't tested the AFM, and I haven't tested the thermo time switch (is there more than one?). What sucks about these idle issues is that there are tons of similar threads but very few with people figuring it out. They test and adjust the TPS, replace the IAC, replace the time switch(es), replace the AFM (I also have a new one I could try that hasn't been opened and messed with), and still can't figure it out. Anyone dealt with this and actually SOLVED it?

It seems to me like if it idles great when cold, then it would make sense for the cold start injector to be involved. Maybe it isn't shutting off, and running too rich. Maybe it being on is allowing a cylinder with a weak or dead injector to fire, but without it, I have a misfire? I'm going to pick up a timing light and do some plug wire pulls to see if I can nail down a certain cylinder that could be misfiring. I'm surprised that I found and eliminated two vacuum leaks and didn't really get anywhere with the warm idle. Cold idle sounds MUCH better with the new TB and idle-up valve replaced.

 

https://streamable.com/w7fu84

video of what it does. At almost exactly 2:00, it goes from running fine to choking and dying.

 

Hi Danson, assuming this is a 4Runner it would be easy enough to pull the fuel pump and take a look in the bottom of the tank to see if there's any junk or sediment type stuff in there, and while you're at it check the sock/filter (idk the proper term). Could also rig a fuel pressure gauge to see if it's dropping when it stalls. Be very careful with those tiny screws in the tank lock ring when pulling the pump they're easy to break off obviously (but what fastener isn't on these trucks?) Mine looked like it had never been pulled so I broke a few screws, but when I took my time they came out fine. Maybe try the pressure gauge first

 

Hey, thanks for the reply. I hadn't thought of the fuel pump because I can drive the thing all over town, highway speeds, never fails to start, just won't stay alive while idling after roughly two minutes. Makes me think it's something electrical because it's predictable -- exact same timing, exact same drop, every single time after a cold start. Throttle also keeps it alive, so I must have fuel. I do have a brand new fuel pump and hanger, so if it comes to that I can definitely rule it out but it's in the other 4Runner.

 

If it idles fine, cold, then the IAC most likely isn't the problem. If it was hanging open then the result when the engine was warm would just be a higher than usual idle speed and possibly a slight lack of power due to un-metered air going into the engine. Check your trouble codes. Often times throttle position issues won't turn on the CEL but will set a code 11. I'd start there - there's lots of good videos on youtube that explain how to calibrate the TPS adjustment. Once you do that you can use the air screw on the side of the throttle body to fine-tune the idle speed.

If you do happen to discover a problem with your IAC, I have a good one for an '86. Came off a running engine, works perfect. Even has all the hoses with it in good shape.

 

Thanks for the offer. You’re right, it wasn’t the IAC (at least not entirely). It was the EGR. Once I blocked it, it ran much better. Still has some little issues here and there but for the most part it’s staying alive at stops and idling fine (if a bit high, but I messed with a few things prior).

So for anyone from the future reading this after nonstop googling, block your EGR at the back of the intake using a cut up beer can like I did. Really easy first step and would’ve saved me a lot of time and effort had I done it earlier. Now on to tackling the rest of the problems, once I get my new EGR valve from 22RE Performance.

 

I have an EGR valve also…lol

 

A good one? Well shucks, I'm sure you want less than $225 for it! They shipped it too fast! I do have two trucks though, and the one I tried cleaning has a bad diaphragm (won't hold vacuum). I actually haven't taken the one off of the truck in question yet, I just assume it'll be bad and/or too dirty to bother with, and I needed at least one anyway. Maybe I could use yours for one of them if I get it off and confirm that to be the case? Also, do you know how to check the IAC? Is it presumed to be working as long as it isn't plugged up, or do they fail somewhere?

Thanks Plarpy.

 

I sent you a PM.