3FE code 51 high RPMs...I'm stumped

[Aggiesdm]

Hi all, yesterday after driving my '91 around for a while, I stopped for about an hour and when I started it again, the RPMs at idle jumped up to 1600-1800 RPMs. Prior to this, it had been running fine and idling around 650 RPMS.

I initially checked to see if throttle cable was stuck, but it was fine. I then checked for a code and it gave me a 51, which points to a TPS issue, but I replaced the TPS last year with a Toyota OEM part. I don't think its the TPS especially since it just changed within such a short time. I read on the forums that it could be APC valve also, but can't seem to find how to diagnose it.

Any thoughts or advice? I use the vehicle a lot for work, so I kinda need to get it back running normally.

BTW, its got 289K miles on it and has a stock drivetrain with no changes to emmisions or exhaust.

 

[mct75]

Oh hi. As someone that can recall the entire FSM section on the TPS by heart now, welcome to the fun.

Go ahead and remove the connector to the TPS and verify the IDL-E2 connection (that's the two bottom most ones) is responding like it should. You should see low resistance (less than 2.3 k ohms) on idle and infinite resistance as you open up the throttle a tad.

You can also check the IAC (the can thing right in front of the TPS) operates like it should. The best test in the FSM is to shut the engine off and listen for the IAC to start clicking. That's it opening up all the way for the next time you crank it.



Just a thought, if you really need the thing to work well for driving, clamp a vise grip on the hose that goes from the intake tube to the IAC. Restricting the air ought to slow the idle down while you troubleshoot. You may have to tap the gas pedal while cranking it though.

 

[LAMBCRUSHER]

you gotta calibrate those things...as the gunk sticks to the throttle body butterfly flap, it stops closing all the way; the TPS gets confused; you get high idle; we get a thread...there are videos showing how to test and calibrate- easier to watch than to read...

 

[mct75]

The crusher is correct. If IDL-E2 isn't being asserted to the computer, it thinks you're pressing the gas pedal down and all bets are off.

 

[Aggiesdm]

Thanks all. I'll try these options this weekend. I'll report back

 

[Aggiesdm]

Oh hi. As someone that can recall the entire FSM section on the TPS by heart now, welcome to the fun.

Go ahead and remove the connector to the TPS and verify the IDL-E2 connection (that's the two bottom most ones) is responding like it should. You should see low resistance (less than 2.3 k ohms) on idle and infinite resistance as you open up the throttle a tad.

You can also check the IAC (the can thing right in front of the TPS) operates like it should. The best test in the FSM is to shut the engine off and listen for the IAC to start clicking. That's it opening up all the way for the next time you crank it.



Just a thought, if you really need the thing to work well for driving, clamp a vise grip on the hose that goes from the intake tube to the IAC. Restricting the air ought to slow the idle down while you troubleshoot. You may have to tap the gas pedal while cranking it though.

So an update. I have not yet checked the TPS, because I just replaced it last year and calibrated it correctly per the FSM. It has worked perfectly fine to date. (I'll try to check the TPS this weekend). I did check the IAC valve and it clicks when I shut down the motor and it shows the correct resistance across the terminals per the FSM.

I haven't removed IAC to bench test it (basically a visual test while applying voltage) but it does seem to be mechanically functional as far as I can hear.

I don't know why, but this whole thing seems to stump me. I generally pretty adept at chasing gremlins. I've read that the AC has an idle kick-up switch (name?) and there is also a water temperature switch that could be at fault?

Any thoughts or help would be appreciated. As stated previously, once the motor is started, it jumps up to around 1600-1800 RMPs and doesn't come down. Its running smoothly, but just not at the right idle speed. Also, this wasn't a gradual change or degradation. It happened in an instant when I shut the motor off for an hour and restarted it again.

 

[Aggiesdm]

The crusher is correct. If IDL-E2 isn't being asserted to the computer, it thinks you're pressing the gas pedal down and all bets are off.

I'll be testing the TPS this weekend, but its acting very different than the first time the TPS was bad. The first time was represented by surging and jumping in the engine speed, while this is just a constant high-idle. Doesn't seem to jive right in my head.

Thoughts?

 

[mct75]

Well, there are two functions of the TPS, the IDL signal and the sweep on VTA to actually tell the computer what the variable position is. On mine the IDL worked but the VTA was screwed up.

I'd really test that IDL-E2 connection. It takes like 30 seconds.

 

[Aggiesdm]

Well, there are two functions of the TPS, the IDL signal and the sweep on VTA to actually tell the computer what the variable position is. On mine the IDL worked but the VTA was screwed up.

I'd really test that IDL-E2 connection. It takes like 30 seconds.

Will do. I'll get on that this afternoon and see what I can find. Thanks for the reply

 

[mct75]

It would also be fun to partially clamp off the hose to the ISC and see if that brings it down to a reasonable level.

 

[Aggiesdm]

It would also be fun to partially clamp off the hose to the ISC and see if that brings it down to a reasonable level.

Hi MCT75, here is what I found. I couldn't clamp off the hose, but I pulled it off and plugged it on both ends and the RPMs came right down to normalish levels.

I then tested the TPS and sure enough, I'm getting no continuity at all across IDL-E2 regardless of what feeler gauge I use. VTA-E2 seemed to be fine, but nothing on the IDL. Guess I'll be buying a new TPS, which stinks since I just replaced it last year.

Any additional thoughts before I replace it? thanks so much for all the help. I was clearly in denial!!

 

[Aggiesdm]

Update: I apparently keep jumping the gun. After I got the Throttle Body off of the vehicle and bench tested the TPS, its seems to working properly. I then removed the IAC valve and bench tested it....dead. It clicks, but won't extend/retract at all. I opened it up and everything is clean and moving freely, but the actuation of the magnet isn't strong enough or something. It clicks and it does barely rotate, but not enough to actually open or close the valve. I did find that the coolant passages were completely clogged with brown/rusty crap. I flushed and cleaned the coolant system when I baselined the vehicle, but I guess it was already too far clogged. I'm wondering if the lack of coolant caused it it overheat and warp the housing or something? Just an idea. Either way, I'm stuck...

Am I missing something or is this thing dead? I've searched around and these parts are becoming super rare. Not sure how to proceed at this point.

 

[mct75]

The coolant lines are there to prevent icing in cold weather, the pressure drop causes the throttle and ISC to get cold. Not sure about the valve itself though.

 

[Aggiesdm]

The coolant lines are there to prevent icing in cold weather, the pressure drop causes the throttle and ISC to get cold. Not sure about the valve itself though.

Good to know and makes sense. I live in South Texas, so don't really have to worry about icing.

 

[mct75]

Mine was clogged with brown sludge and I removed the coolant lines for that and the throttle body with no ill effects.

I haven't taken my ISC apart yet but I do know they sometimes get blocked up.

 

[Aggiesdm]

Mine was clogged with brown sludge and I removed the coolant lines for that and the throttle body with no ill effects.

I haven't taken my ISC apart yet but I do know they sometimes get blocked up.

Have you ever heard of rebuilding the IAC (ISC) before? It doesn't seem complex at all, but there must be some circuitry inside of it that tells it when to reverse the polarity on the charge. The valve is actually a screw type mechanism that extends and retracts the plunger by spinning on a bearing. The bench test has you apply 12V in a sequence from pin 1 to 4 for a clockwise rotation (extension) and from pin 4-1 for retraction. When I test it, its trying to work but not actuating enough. I made sure everything is clean, lubed and free in the guts of the mechanics, but the electrical portion is sealed inside the body and the body is molded around it, so no access.

Thoughts?

 

[mct75]

The wiring looks to me exactly like a stepper motor, with nothing but coils and magnets inside it. No real "electronics" to speak of. The ECU just sends pulses one way or another to tell it "open up some more" or "close down a little." The clicking when you shut the engine off hints towards this as well, it's just opening up all the way so the engine restarts easier. I highly doubt it has any sort of position sensor inside it.

Dumb question, but what 12v source are you using to drive the coils? If it's something that might not supply a lot of current (a 9v battery or something) I could see it struggling. What are the resistances on your coils? I'll measure mine and see what it is.

 

[ppc]

The IAC moves very little for each pulse. Just going through the 1-4 combination one time will not cause much movement. Don't expect it to travel it's full distance for the test by any means.

 

[Aggiesdm]

The wiring looks to me exactly like a stepper motor, with nothing but coils and magnets inside it. No real "electronics" to speak of. The ECU just sends pulses one way or another to tell it "open up some more" or "close down a little." The clicking when you shut the engine off hints towards this as well, it's just opening up all the way so the engine restarts easier. I highly doubt it has any sort of position sensor inside it.

Dumb question, but what 12v source are you using to drive the coils? If it's something that might not supply a lot of current (a 9v battery or something) I could see it struggling. What are the resistances on your coils? I'll measure mine and see what it is.

I was using the main battery as my 12V source, so it should be fine. Maybe its actually working the way it should and just travels with small incremental pulses. I'll put it all together tomorrow and see if it works ok.

BTW, I checked resistance across all the pins on the IAC and they were all within spec at about 25 ohms.

If it does, then I'm still stumped at the cause of my high idle. I did clean the throttle body really well, so maybe that was the issue?

 

[Aggiesdm]

The IAC moves very little for each pulse. Just going through the 1-4 combination one time will not cause much movement. Don't expect it to travel it's full distance for the test by any means.

That's good info. I was expecting it to fully extend or retract with the 4 pulses. I'll button back up and pray for a solution.