UPDATED: Problem was solved: bad valcve clearance, losing compression. Read for results.

I am very new here...Like this is my first pick-up, first yota, and first rebuild (I've done bikes and dirt plenty). I picked up my 89 PU with a hell-acious knock. Rebuilt motor-crank, 1 rod, rings, bearings, timing set, oil pump, yadda yadda, but didn't touch valves, they were fine. So I finally get the bugger done and she fires up! So excited until,(que scarey music). It idles like crap, like it's missing. Plugs and Wires are nice and new, cap and rotor good, can't find any vac leaks. Cleaned all injectors, and checked everything I could think of through. It starts mint, picks up around 1k, settles down a little, then when warm drops to 300-500 running rough, sputtering, missing the whole time. I've already doen plenty or readig and searching on here. Throttle body is clean enough to store surgical equipment, and everything moves and operates as it should. I just need some help on where else I can check or should start checking. So far I am digging my first pickup, even though i had to work on it, i enjoyed it.

 

is your intake comming from your airbox to your throttle body all sealed up?

 

Yah, I went through everything a few times just to try and make sure I wasn't missing anything. I could add a bit more info too. 89 xcab 3.0 5sp 144k miles. I keep pulling the plug wire off on pass side closest to firewall, and it has no effect. I thought a short or dead wire...nope, and plug sparks nice too. But I am not sure about this, when turning motor over to check from spark from that cylinder (plug hole open) there was no smell of gas and the plug always comes out crispy dry. I am tending to lean toward a fuggered injector. Anyway to test these things? Timing is on the mark, solid spark, fuel is definately filling the rails cause every time I open it I make a bigger mess in the drive. I was gonna try to yank the TPS connector when I got home from work. Does anyone else have any suggestions for quick multi-testing procedures. Like pulling a wire will eliminate a few possibilities or something. OH! the one thing is, My oil pressure sending unit. I got no readout on my gauge. I have oil for sure (new pump and cleaned out plumbing while it was open and no knocking), but wondering if it's signal is used by the ecm for anything.

 

Sounds like you may have a problem with your wiring harness....

 

I re-groiunded a few of my grounds, I don't think it made much difference. I pulled the TPS connector and the idle spikes a bit then settles a little higher than originally. I also backed my idle screw out 1.5 turns from the original 'in til stop'. I'm at 800rpm idle, ~10deg (close enough), but i still get the lub-lub-lub like it's a V-8 camaro or trans-am or something. And it doesn't really still feel smooth. Near the higher end of rpm she starts to smooth. It feels like it might be dragging one or something.

 

check the fuel injectors/harness.

also, disconnect the cold-start injector clip from the cold start injector.

 

I'd check the injectors then. Look in the sticky posted at the top of the forum main page for FSM links. You'll find how to check the injectors there.

 

Good suggestion!

If the cold start injector is "stuck", it could be leaking more fuel into the system causing it to run too rich after it's warmed up.

 

Thanks for the tips. I've been reading so friggin much as of lately. It almost seems like a common issue that people just deal with, but it annoys the hell otta me. I was really NOT wanting to rip off the plenum again for the third time in 2 days! What a $h1tty task it is. I did get new plugs, the ones in were platinums and beyond their limits. I got spark through the wire to the plug and the plug is sparking. (cylinder 3) So my pops thinks it might be a bent valve which I am highly doubting, but we will be doing a compression check on that cylinder then I am pretty sure I will be ripping off the plenum. Thanks for the help and I'll keep everyone up to date.

 

did you try disconnecting the cold start fuel injector wire connector?

 

Since you said it idles rough I'm assuming it runs smooth under load/higher rpms?
I'd check for a stuck EGR valve or a bad EGR transducer opening the EGR valve at idle.

 

I have the same problems with my 88 runner. we call it a 4 banger now,
Ive bought every thing for it from wire harness to spark plugs and changed every thing I could short of a engine rebuild ,even though I replaced the motor 3 times with junk yard motors and no luck. and sending it out is way to much cash.
I'm thinking of just buying a 92 and up rolled or wrecked 4 runner to swap out every thing.
I have had the problem for 2 years now and Im sick of spending money on it and NOT fixing the problem.
I solved it by the old fashon way.I bought a fj
so I feel your pain.

 

if you've replaced the motor 3 times and you still have the same issue, it's not the motor, its your ignition coil or fuel pump/lines or something.

 

Yah, if you are talking motor replacement, with same issues. CHECK WIRING and electronics. I did the compression test. What a ty gut-wrenching feeling it is to watch minimal gauge movement, and know you gotta rip-apart a motor you just finished putting together. Under cranking good cylinders gave readings of 125psi. The dead one gave me 25. yah, 25 minus the 1 in front...So I am going to rip it apart again reseat the vavles in that bank, check all my wiring and injector testing while it's apart. I dunno what to look for. bent stem, bad spacer pucks for valves, wtf! thanks for everyones help so far. I've seen this problem mentioned lots with no solutions. hopefully this will work out for me.

 

i had a problem on a 88 4runner i bought that had the exact symptoms yours talking about i went through everything finally did a compression check and found no compression in cylinder 5... pulling the valve cover and checking the clearence i found that when the motor was put back together by the previous owner they mixed up the valve shims... so the valve was never seated and the gas was blowin right through the cylinder.. a little bit of work and she was runnin strong again.. just an idea of somethin to check. good luck!

 

thanx for that post brandyn85. Kinda what my dad was getting at was that we goofed shims when putting them back in. But I labeled them before removal and installed with double/triple checking. BUT, regardless...I am going to be stripping it back down and doing the work. I am hoping to find some shim issues or something nice and easy to replace. Then again if i go that far even replacing a valve becomes an easy task. I'll keep up info if I find anything different.

 

those motors are real good for burning the valves make sure the valves are seated correctley and adjust valve shims to spec I work at a toyota dealer and this is very common to see happen if all is adjusted correctley message me and I can help from there

 

Did you do a compression test? i'd check that before tearing it down....

 

thanx. Yah compression check on all cylinders gives 125 on the nose for all cept for #3 @ a whopping 25psi. as of right now i've got everything off and am looking at the cam. I am looking up for the clearance i need between the cam-lobe and shim to see if I mixed them up or they were mixed up before, or maybe everything is just out of spec. Will keep informed as soon as I get more info. Thanks for the help linkedrunner.

 

DAMN IT! Head is apart again. Dad checked valve shims..still crappy compression. Head came off. Did a water test, invert head poor in water, watch it leak. ex valve is leaking. noticeable....ike within a minute or two. Changing out valve, possibly valves.