This is for an engine from a 1995 T100 3.4L 1t. Had it in my 4runner for a while now, sounds good. No codes.
I have an intermittent hard start (many many cranks) issue and OCCASIONALLY ill get a violent intake backfire after like 2 cranks, after which it hard-starts. I will try and describe it below, looking for some troubleshooting tips/ideas and maybe experiences to help me narrow down the problem... If I had unlimited money, id just replace the whole Throttlebody and all the injectors and the FPR and the fuel pump and etc etc etc but i dont want to just throw money at it blindly.

So it seems to depend on temperature and time.
When its been sitting for a long period, it typically starts almost TOO fast. Every 5vz ive ever started usually takes 4 or 5 cranks to start (ie er-er-er-er-ROAR). Mine is just one crank most of the time!
So say im headed to town. I start it up (er-ROAR!) I drive 15 minutes to town, I park in front of the post office, im in and out pretty quick, its a "normal" start, 4 or 5 cranks.
Maybe I go to the bike shop and spend some time having a beer and bull˟˟˟˟ting with the guys. im in there 20-40 minutes. Back to single crank fire! Then I drive home and im working in the shop for a couple hours. Towards the end of the day I have to run back into town for a part. Boom hard start. Like 10 cranks, pause, 10 cranks, pause, 10 cranks, pause, 10 cranks, half catch but dies, 10 cranks, half catch but dies, 10 cranks, stutters to life very shakey and low rpms, NO CEL!, slowly recovers.

This also happens when I go ski touring almost without fail. Ill drive out, park it at the bottom of the mountain, ski for 6-8 hours, very hard start.

Ive found that while hard starting, if i give it a little gas pedal, the open throttle helps it start faster, but it still kind of struggles. im TOLD by my partner that when it does finally start, theres a puff of black smoke. These two things lead me to believe its RICH by quite a bit....

So now onto the backfires! SUPER occasionally when I go to start it it will backfire loudly and violently. Partner tells me she sees gas ejection from the engine bay! (not fuel, like a shockwave) then its ALWAYS hard to start after that. pedal helps it go, partner says black smoke again. This is WAY more intermittent, seemingly random, but always right after first crank. I strongly suspect the problems are tied.

Ive watched MAF signal and ECT signal and both seem pretty steady and sensical. Ive removed and cleaned the IACV. It was pretty dirty but this hasnt seemed to have made a difference. Ive replaced the TPS with a $$$ toyota part because im an idiot and I thought it going from 17% to 75% through the full range was a problem, when it turns out thats how its supposed to work... I tuned it/set it up according to the FSM. When i dropped the engine in I put all new 2 electrode plugs and wires. Coilpacks test good. I just used the old 3.0L fuel pump because the internet told me I could. Replaced the filter. Most if not all the vac lines on the engine are new. The throttle butterfly valve has a little play in it as the bushing on the pivot is worn. I added a nylon washer and some grease and its allowed it to return closed well enough that the truck idles perfectly.

Im at a bit of a loss here.. I SUSPECT a leaking injector, based on basically no evidence, but my theory fits the symptoms... which is a bad way of troubleshooting. Seems a bit like it bleeds down into the intake when it sits pooled. If I start back up again quickly theres not enough fuel for it to effect anything, but if it sits for a bit it wets a plug or something when it pours into the cylinder. Then if the valves and wasted spark configuration work out just perfectly, it ignites the vapours in the intake manifold, causing the rando backfire... One of the injectors is wet at the top, which MAYBE is indicative of an internal leak??

Edit: the other thing I maybe should mention is that when im driving and giving it gas, and i let off the gas and clutch in, the revs climb a noticeable amount. Dont know if this is a slow closing bellows on the throttle dampener thing, if its NORMAL, or what... Maybe you can tell me. For example, driving up a hill with lots of throttle, let off to shift gears, rpms jump maybe 500 then fall. If i wait maybe a half second between off gas and in clutch, they hover for a half second before dropping. Full second, they just drop. normal? weird? you tell me.

WHATS THE NEXT STEP HERE.
Is there any way of confirming my theory? Can I cross everything else off the list somehow? What do i do next???

 

well maybe I write too much and it scares people away.

Just decided to say ˟˟˟˟ it and buy a new FPR and a new denso fuel pump, along with a variety of relays just in case, plus a set of 6 o-ring kits for the injectors. In the spring i will pull the intake and add the FPR, change the fuel pump, and send all 6 injectors somewhere to get tested.

Way I figure it the FPR and fuel pump should just get replaced anyways. Things at 207,000 miles.

Oil sample is on its way to blackstone to look for fuel... I will keep this thread updated because I dont want someone else blowing all their hard earned cash on guesses haha