TPS Voltage Adjustment on 96 Tacoma?

96 Tacoma, 2.4L automatic. Idles at 600RPM which makes it idle rough. NO CEL, no codes. Sensors all working properly, no leaky injectors, IAC is clean, TOP end is clean, etc, etc. On a 96, is it possible that the TPS voltage is off? If I have the truck in gear, hold the brake with one foot and slightly push the gas pedal to get the RPM up to 750, you almost cant tell the engine is running it is so smooth. Im baffled

 

just like my 97.
only vibrates while stopped in gear.
I was thinking of trying to replace my iac, when I replaced the gasket I wasn't sure if it was actuating properly.
if you change your tps, please update if your low idle is fixed.

 

Same issue with my 99 3RZ. I have gone through and checked everything except pulling the EGR valve. It could be sticking slightly open at idle.

I have also read that it could be a problem with the computer and the only solution is to replace the ECM.
https://www.tacomaworld.com/threads/2-7l-rough-idle-diagnosing.466233/

 

I will add that I am currently at 200,000 miles. The valves were adjusted/pucks replaced at 175,000 miles. The truck runs like a champ and has never stalled or even had a hickup. It just idles at 600rpm in gear and shakes. And I might add that at 600rpm, the needle on the tach doesnt bounce or move at all at idle.

 

How are your motor mounts and transmission mount? All 3 of mine were bad and cracking apart from the metal. replacing them helped but the vibration is still there.

 

They were replaced at about 150,000 miles. That still wont cure an idle at 600rpm. It is something sensor related im sure. Im going to clean the EGR temp sensor next and see what it does.

 

Yes I agree with you 100%. Something is causing the engine to idle slightly lower than normal. I cleaned and tested the egr temp sensor, cleaned and tested the MAF, cleaned and tested IAC, cleaned the throttle body, cleaned the PCV, tested the VSV for EGR, decarbed the engine, checked and/or replaced all vacuum lines.

My idle is still around 630 while in Drive with the brake on. The truck shakes much more than when in park or neutral with the idle right around 700 or slightly below.

 

You just described my situation exactly.

 

Did you guys ever get a resolution on this? I have 2 1999 taco's that are essentially identical. The "good" one idles around 1050-1100 (going off the tach, haven't checked with a scan tool lately). The "Bad" taco idles around 650. I cleaned the intake, MAF, new intake hose, checked for leaks post-MAF sensor, new plugs, wires, etc, etc. Truck slightly shakes at this low idle. What controls idle speed on these trucks? I thought about replacing the IAC valve however that's a pricey part to just throw at the truck and hope it fixes it. Seems like TPS wouldn't cause this as it should be reading 0% throttle, unless the proper adjustment at the intake has the TPS off its 0% bottom when there is no throttle pedal pressure. My next step is to read the FSM and see where all those little set screws need to be at where the throttle cables actuate the butterfly. Curious what others have done...

 

I'm still fighting with mine. My idle in drive drops to 640.

Have you compared sensor data between the two trucks?

 

Hey @MikeWH, can you tell me what your VSV for EVAP does at idle when warm on both your trucks? The VSV for EVAP is the vacuum switching valve mounted at the back of the charcoal canister (firewall side), one vacuum line comes from the throttle body, the other goes to the charcoal canister.

On my truck it is clicking at idle, like it is rapidly switching on and off. I can touch it and feel the magnetic switch moving. I can read via a scanner that it is not "active" at idle. Once I press the throttle I can see that the computer is sending a signal to open it, but this doesn't explain the clicking.

 

nzbrock- Hoping to compare them side-by-side this weekend or middle of next week. Will post anything of interest.
On the VSV valve- is this the one with a shock absorbing rubber mount? If so, my recollection is that it pulses rapidly (which is why it's shock mounted), like a couple times a second, and you can definitely feel it going! I will have to check with the trucks running though, as I don't recall if this is cold/idle only or at all speeds/temps.

Anyways, glad to compare notes with you, just need to get out and start the trucks up.

 

Definitely let me know. Although I did more reading and the rapidly switch VSV for EVAP is normal operation.

 

I've been experiencing similar issues to this with my 97 Manual. The tps is reading at 11.4% at idle and I'm sure it's in need of an adjustment or replacement. For the OP, I would use a feeler gauge and check the tps for the right voltage at throttle release. I'm gonna be digging into mine soon and will post updates accordingly. If you cleaned the throttle body recently, then the older tps is probably out of sync. Had that problem with my mr2

 

I know this will sound like horseshit but I had a code for the tps and bought the sensor and took it to a lexus/yota tech and he threw it on and said it has to be clocked pushing it against the screws clockwise. I kinda laughed because my tps doesn’t have slots to really move it but he showed me on his snap on gauge that it ohmed out differently if clocked incorrectly. Fwiw

 

I spent several painstaking hours with a multimeter and a Frankenstein of a #2 phillips bit and extension, to get just the right length. good god who is responsible for using phillips on these? Cannot believe i didnt strip the head. adjusted screws and "clocked" tps per fsm instructions. the durn thing still has a semi rough idle in drive with foot on brake pedal, and intermittent hiccup at 70-80 mph. Interestingly more pronounced when crossing the "wash" or "wake" of the low/high pressure zones created by other vehicles on the freeway, i.e., going from drafting closely to the adjacent lane, but frequently happens when passing. Never present at low or high rpm, i unfortunately dont have a tach in my taco so not 100% on rpm range. my next move is fixing to be replacing that tps, but it tested good during that clocking session, so i have some trepidation in throwing a nearly two hundred dollar at this infernal problem. perhaps i should save my pennies for an oscilloscope and do some real in depth diagnosis.

 

Do a search on this forum for a thread titled "Bad Shake at Idle" he has a solution.

 

Mine was fixed with vacuum hose replacement. Especially the the brake booster one

 

Mine was my exhaust bouncing around.
https://www.tacomaworld.com/threads/2-7l-rough-idle-diagnosing-solved.466233/