300,000 Mile Gremlins

Hey Guys,

I have a 1996 Taco 4x4 with 3.4L. Just about to hit 300,000.

I am trying to troubleshoot all the gremlins I inherited since I purchased the truck at 260,000 miles w/ a 3" Lift, Super Charger and a bunch of Upgrades/Mods that I am still discovering.

Experiencing a Rough Idle and High RPM ~1600 and slowly goes down when i cold start the engine, but once it enters closed loop it seems to smooth out.

Just picked up a BlueDriver obd2 scanner and took it for a ride today to check out my levels.
RPM idle ~850 while in park and ~700 when in gear.
TPS goes from 5 and tops out at 65??????? with pedal on the floor(dont know why its not higher)
ECT never got above 185.
STFT was ~-7 at idle but goes down to 0 upon acceleration.
LTFT is ~-15 at idle and ~0 upon acceleration.
Timing advance ~17 at idle and up to ~30 during acceleration, if i remember correctly.

These Readings Seem About Right? Any Other Readings I Should Focus On?

I was suspecting a MAF sensor issue, but the IAT seemed good and I dont know shit about LB/Min, so hoping some one knows.

Other Problems/Concerns:
Suspension is so stiff
Ball Joints
How Do VSV routed and when are the supposed to be on?
~12mpg

Things I've Done:
Brake Replacaements/ Flush
Engine Rebuild (With Help From A Buddy)
Removed Super Charger
Front Crank Seal
Heater Core
HVAC Mixing Unit Restoration
CV's
Fluid changes
Bunch more I'm forgetting

Didn't know any thing about cars and this was the platform I chose to learn on. Love the truck, but age takes its toll. So am trying to learn how things are supposed to function to troubleshoot and identify what part needs to be replaced. Doing it by myself in my spare time. Really trying to embrace the mechanic within.

Any help would be awesome, Thanks in advance!
-Tom

 

Clean or replace the IAC and clean the TB while you're at it. However high idle is normal for initial cold starts, rough idle no.

 

@zero4 Thanks for the quick response, I cleaned the throttle body last summer and noticed the IAC was looking kinda haggard. I shot some cleaner thru it, but now that u mention it I should prob revisit. I figure it has to be some sort of engine sensor because the problem happens in open loop.

 

When the engine is cold it should be in open loop until warmed up enough. Also, in open loop I don't believe the ECU reads (cares about it) IAT, ECT yes.

Simply spray cleaning the IAC doesn't always work. That's what I used to do & would have to clean mine every year & half or so. Last time, I gave it a really good cleaning, the cylindrical valve slide thingy is what really needs a good cleaning. Been years since mine has acted up since. Which reminds me, I should probably clean it soon just for maintenance.

BTW, before someone else says it, Toyota recommends not to clean the IAC, replace only. Well so do other OEMs. I've always cleaned IACs on Toyotas & Hondas with good results.

 

I also had a high idle last year. New Denso IAC and rebuilt TB by MaxBore seemed to fix it. I’m also getting ~12 mpg with 33s on 3” lift. Others with similar setups are getting the same as well so ~12 is probably normal.

 

Did you check valve clearances as part of the engine rebuild? Also I replaced my original coil packs a couple months back with new OEM ones and my MPGs seem to have bumped up from ~13, to ~15 after doing so. That's all city driving with 31" x 10.5" tires.

 

@zero4 Just got done with the IAC/ TB cleaning. TB was pretty clean, IAC was a little scummy, but still seemed to spin. I will update after cold start. Classic fashion with this truck, gotta drill out something that's stripped to do a repair. Somebody had been in there before and loc tite'd the shit out of em and gasket goop everywhere.

@Logans2001 Yeah mpg is nothing to brag about with my 32's

@Red_03Taco Yup valve clearances were good when I put the motor in the 3rd time. (I bought a Japanese motor online and it must have come from a different year or something. Finally realized the bolts on the flexplate were preventing it from mounting to the bell housing. they were .00004" too long and were causing interference. Put the old motors bolts in and no problems. Not the most fun feeling with the engine of my DD hanging from a hoist after dark, on a Sunday with work in the morning.)

 

Cold Started the engine this morning and Idle RPM was down to ~1100. Seems to have worked! Thanks for all the input guys. Today I will get after the loose Gear shift Bushing Replace. I'm sick of the key getting stuck in the ignition!!!!!!!

 

Also when you buy a new IAC is it just the electrical component and none of the mechanical parts that become dirty?

 

Its all one unit....

careful when you clean and try not to soak the solenoid....

 

You do want to take your time when you put on the throttle body...

if you screw that gasket up......water straight down the intake......would be berry berry bad.......

 

Your TPS is not on schedule. There could ne dead spot in its rheostat, causing mis-reporting to the ECU. My original went out after 360K miles. Smooth operation after replacement; there was no CEL.

 

@O'Silver_Taco I took the Solenoid off before giving the valve thing a generous cleaning. I hit that gasket with a little gasket goop too. Hopefully that doesn't mess anything up. Let it sit overnight before starting.

@phoenix ray I'm not noticing any weird throttle response, but I guess throttle is cable controlled. What kind of symptoms did you have before replacing TPS? I am concerned about the transmission shifts between 1st and 2nd, they seem to be a bit delayed. Not the worst, but I thin they should come sooner. I don't know if this could be attributed to lift and 32" tires. The specs for the shift points in the Factory Service Manual are for stock tires sizes.

 

@phoenix ray I Tried replacing TPS with an aftermarket TPS ,but the ecu also read only 65%. Weird.