3vz won't stay running after it warms up????

[moyabeans]

So hey all this is my first post and sorry for it being one that involves picking your brains, this issues has me to the edge. To start off I have an 88 4runner 3.0 owned and driven everyday for 10 years (my first toyota that I bought at 17) I have done and maintained it this whole time with the help of my pops who has been a mechanic for longer then I've been alive.
Now let's cut to the issues it's started out as a gradual lack of power kinda bog like, hesitating while driving for a few miles, I first noticed it when driving through a spring blizzard in the foothills of colorado so I wasn't sure if it was road slush at the time. The next day the sun came out and cleared the roads prob back in the 60s or something (if your from colorado you know what I'm talking about) but on the way back down to town it started to act out again. It was pretty intermittent at this time about a few miles every time I drove it then it would clear up on its own. It's has gotten worse as the weeks have passed. Now it's nice and hot here in Denver and I can't drive my truck more then a few block with out it bogging down and dying and won't run after that till it cools back down. So basically it's starts up fine everyday till it gets to operating temp then the idle bounces a bit from 1000 to 1200 to 900 to 500 to 800 to 400 to its death. I can start it right back up and it will kinda idle low till I push on the gas and either it will die or build up rpms to about 3000 then die back down. It's been sitting in the driveway for 3 weeks now and that's the longest it's ever sat in 10years and I'm about to start my second semester of paramedic school in a month and need my whip back!!!!! Any help would be appreciated and needed at this time thanks a ton guys for any ideals to check or look into.
Now to what I have done changed out MAF, TPS, throttle body cleaned, fuel pump, TCS, cap, rotor, plugs, coil, ignition module, checked for vacuum leaks,

 

[moyabeans]

Also forgot to add its a 88 4runner 3.0 that I think was out of a 89 manual trans only motor upgrades would be a K&N intake that's been on for 6 years or so and a flex fan, I also changed the fuel filter

 

[SV_Dude]

How many miles on the engine? Just to rule out an old tired engine, have you done a compression check?

I assume you're not getting any check engine lights?

Something worth a check as well is your ignition timing. I don't remember what it's supposed to be at for your engine but even if it slipped a few degrees could give you the problems you're having.

Btw: welcome to the forums!

 

[moyabeans]

Miles I'm guessing around 220,000-230,000 I had a problem with switching out instrument clusters when I was a bit younger. I'm sure the engine in fine cause it runs and sounds great and only acts up when it gets to operating temp. And I'm not totally a box of rocks but when you say the ignition timing are you talking about adjusting the distributor? Cause that might help woundering if it going bad inside I'm not mistaken it might have somewhere around 380,000 miles on it. Thanks for the help so far

 

[SV_Dude]

Put a timing light on and verify the ignition timing a set correctly. Your coolant temp sensor may be bad also. See if you can find a fsm for your engine, grab a multimeter and start testing your sensors. Odds are you are ether out of timing or have a bad sensor that's feeding your ecu some bad info once warmed up.

 

[crash813]

Think about what changes the engine mgmt is doing when it reaches temp.

Main thing I think about is it switches from open to closed loop and starts using the 02 sensor. Checking out that as well as the ECM itself.

 

[SV_Dude]

Think about what changes the engine mgmt is doing when it reaches temp.

Main thing I think about is it switches from open to closed loop and starts using the 02 sensor. Checking out that as well as the ECM itself.

It does a few things when it does that. The ECU advances the ignition timing, takes input from the water temp sensor, maf, tps, and the o2 sensor.

 

[crash813]

It does a few things when it does that. The ECU advances the ignition timing, takes input from the water temp sensor, maf, tps, and the o2 sensor.

Yes, but when it open loop, its still reading the afm and tps accurately enough to let it idle good. As far as timing, if it starts to advance and starts mising, it'll pull it back. That's why I would start looking at the O2 sensor next. Or atleast, the mental checklist I start going down when thinking about stuff like this. The other thing I would check is fuel. In open, it runs much richer plus at cold temps, you get the extra injector which may be keeping it just rich enough to keep it running. At idle without that, it may not be getting enough fuel to keep it running.

Last thing I always double check, esp when idle is screwed up is vacuum leaks. I know he checked, but I double and triple check. When I was having all of my issues, I started plugging all of my ports one at a time to see if there was any improvements.

 

[giro]

There's no check engine light on, right? I don't know about the '89 3.0, but the FSM for my '92 3.0 gives the details on what throws a temporary CEL, and what gives one that sticks around until cleared. Obviously if the light is on, get the code to narrow things down drastically.

You might want to check the connections and plastic from the MAF to the throttle body. On a 3000gt I worked on for a while (much different beast, but similar ideas) I popped off an intercooler line (basically an air line after one of the turbos and after a cooler) when I downshifted getting off the freeway. After that, whenever it got up to temp and started using the sensors, it would throw black smoke and lose all power. The data from the MAF doesn't mean much if it's sucking in air after the MAF. And that didn't throw a CEL.

BTW, if you really need to use the truck a little, the "limp home mode" should allow it. Disconnect the MAF (which will give a CEL), and it will keep you in "open" mode, not using (or fully using) the sensors. This isn't ideal since you're then probably spewing bad emissions, eating gas, and likely sending extra gas to the Cat which can foul it. But if used minimally, like a trip to the local parts store or escaping a fire (had our first local fire for the season between here and Reno, and then it rained and snowed a lot (for a May storm)), it shouldn't matter too much.

 

[moyabeans]

Thanks guys for the input so far.... The only code showing at this time is code 42 which I think is VSS vehicle speed sensor that I guess is in the back of my instrument cluster I don't think that would be giving me the issues I'm having. Going to try and clamp off my fuel return line this weekend and see if that helps maybe I have a bad fuel regulator letting to much fuel back down the system making me "lean out" in a way. I have tried the limp mode but still no good when warm. And also took out the o2 sensor while testing to rule out a clogged cat and faulty o2...... Still lost for now I'll let you know in a few day if this works out, thanks again guys. Chris

 

[moyabeans]

Figured it out the other day.... Jump the fuel pump after it stated acting up and it fixed the issues so then I was on mission to figure out why I started with the open circuit relay behind the glove box swapped it out and boom it was fix been driving it for a two weeks now with out incident. I guess water has been leaking down on it cause it was all rusted. Thanks again for all your help guys and glad to have my 4runner back..