Chuki

Testing my o2 sensor today, I noticed something odd. With my E1 and TE1 connected (y'know, how you pull the engine codes) at an idle it just blinks like normal, but when I give it throttle it gives me a code 51.

It idles alright, a tad rough but nothing to serious I would think. Did some searching and turned up that it is mostly caused by a bad or misadjusted TPS. So I want to throw into the equation, when I turn my A/C on it idles up fine, but it runs really rough. Without the A/C its smooth.

I get this code without A/C on.
Any ideas?


**EDIT** 90' 4Runner 3.0 V6

Chuki

did some more fiddlin around, I think I'm gonna chuck this up to a bad TPS or misadjusted TPS.

Idling everythings fine no codes, if I slowly push the throttle once I open throttle to a point the RPMS jump to say 1400-1500RPM or so code 51. Idle everythings fine... A/C Switch on, code 51..

Basically other then barebones idling with no A/C, I get code 51.

**EDIT** when I press the throttle enough to get it off idle, it runs rough, I'd say 1400-1800RPM it runs fairly rough, after that engine is speed is probably too high to tell if its running rough or not. But I still get the code at high RPMS as well.

Anyone wanna confirm or deny my suspicions on a bad/misadjusted TPS?

rdharper

Based on a case of three examples, here is my test for a bad or misadjusted TPS.

Disconnect it. You will get the code 51 of course, but here is the point. I believe if the TPS is not present, the ECU does not respond to the readings it is getting from the TPS, essentially bypassing it.

If the problem goes away, the TPS was/is bad or misadjusted.

Chuki

I did what you said and without it hooked up, it idled smooth as glass, with A/C on or anything it was smooth as butter...

I'm assuming its bad, cause when I'm not on the throttle or using a/c it reports no code but when I give it any kind of throttle immediently code 51.

Would hurt anything to drive without it hooked up? Engine felt a 100 times more smoother without it.

rdharper

Won't hurt anything to run with it disconnected. Depending on your ECM, it will throw a code if it doesn't detect the TPS. Some countries don't care, so no code is generated. The code doesn't mean the vehicle is not working correctly in this case, just that the TPS is not present.

There is a good chance it is just misadjusted. But getting it adjusted correctly seems to be difficult "by the book" in a lot of cases. Not sure why. I ended up setting mine while the engine was running, just loosening the screws enough to allow me to twist the TPS looking for that knife edge point. You will probably have a higher rpm for the correct final position, which would be the same as with the TPS disconnected.

Hope that is clear. Very confusing as the whole way it operates is somewhat counterintuitive which is a byproduct of the reason it was put in, in the first place.

Chuki

Mine only throws a code if I have it diagnostics mode, if not... It wont trigger my CEL, although my idle without it connected is a little high and a tad rough, with it connected its reverse idle is smooth, but low rpms and off the idle circuit makes the engine run rough.

When I cleaned my throttle body when I re-did the headgaskets I saturated the entire tbody with cleaner, although I didn't directly squirt the sensor itself I'm sure it got a little wet with cleaner.

If the TPS can be responsible for poor fuel economy, hesitation, rough idling, what is its role in relation to the ECU? What exactly is the ECU using it for?

I'm asking because when I cruise with the throttle around 60-75% up a grade and then let up on the throttle I get a code 25,26 which is lean and rich at the same time. I'm diagnosing that when I stumbled onto code 51 while back probing my o2 sensor.

rdharper

The TPS gives two outputs, one which is like a switch, telling the ECU whether the physical position of the throttle is at idle, or not. This is the one that seems to give the most common problem. If the physical idle is not detected, the ECU decides the engine is idling too fast. This results in the 500rpm which a lot of people with TPS problems report. I think that is just a requirement set up by bureaucrats that have this vision of millions of cars in california idling too fast, polluting air etc. So they require this algorithm. If all other factors say you should be at idle, but the physical position says you are NOT at idle, cut the rpms to 500rpm. "that will get their attention"

This is why you usually get a higher rpm when you disconnect the TPS, as the ECM makes no correction. This would also be the rpm you would get if you adjusted the TPS correctly such that physical idle is detected correctly.

Hope that is clear. It is very much counterintuitive.

The other purpose of the TPS is a signal proportionate to the angular position of the throttle. I've not figured out how that might cause problems, but my guess is that it is relevant to the 2-3k rpm changes we all notice in power output. It is the switch problem described previously which is the common TPS complaint.

So to answer your original question, it is my opinion the the TPS is totally unnecessary for correct performance, but is put in an attempt to satisfy someones idea of proper emission requirements. I visual him sitting on the 8th floor of a Sacramento government office building, pulling in 120k a year for his 32 hour "work" week, trying to figure out how to quailify for early retirement. In my more cynical moments, it gets much worse.

Chuki

With the TPS hooked up mine idles perfect fine, right at 800rpm and smooth as it should be... It's when I pick the RPMs up to around say 1200-1600rpm it gets rough. If I disconnect the TPS, at 1200-1600RPMS it smooths out

I'm a little confused...

With my TPS hooked up, and in diagnostic mode, I only get code 51 if I turn the a/c on or depress the accelerator... I'm trying to figure out by reading the FSM if thats normal. Here's what the manual says for it

Code 51
Displayed when A/C is ON, IDL contact OFF or
shift position in “R”, “D”, ”2”, or ”L” positions
with the DLC1 terminals E1 and TE1 connected.

I guess I just need to whip out the damn ohmeter again.

Chuki

just hooked an ohmeter up to it and everything checks out ok... I could adjust so its on the idle circuit a little better... Right now it makes the transition from the idle circuit about .012" instead of the .020" like the FSM states.

What I find off, with it hooked up I have a good smooth 800 rpm idle, but when I turn the A/C on the RPMs increase to 1100-1200 it gets really rough, if I have the a/c off and press the gas pedal to increase rpm it jumps to about 1400-1500rpm its still rough, with the tps disconnected it's smooth as glass.


*EDIT* I followed 4Crawlers article on TPS's, if I hook up VTA to E2 and watch the resistance when opening the throttle right at the very beginning, if I slowly open the throttle the resistance will begin to increase, then I'll get a slight drop in resistance I would have to guess after opening the throttle about 1/16th the way open, then after that the resistance will begin to climb up again.

**EDIT AGAIN** contacted local dealer for pricing, told them what was going on, he said thats normal. That is the sensor transitioning from the idle circuit to the valve throttle angle circuit.

I was messing around with it some more, and the idle nor running condition of the engine changes with the TPS at all, maybe it was a freak occurence or something I don't know... I'm thinking I have either have a leaking or clogged fuel injector.

rdharper

It is helpful to note the resistance values. Measuring the full range gives the following:

On the idle switch circuit, I get <19 ohms up to the open condition.
On the angle detection circuit, I get a continuous smooth increase from 50ohm to 5500ohms. No discontinuity or drops. (that might indicate a damaged part of the phenolic strip)

Further, at the knife edge point where the switch circuit goes from 19ohms to open, the angle detection circuit is reading 880ohms. These readings satifsy the chart shown in the documentation on the TPS.

Chuki

on the angle circuit I as soon as I start to move the throttle, I get a drop in ohms, and then they increase...

Yours is a smooth from completely closed to completely open? No drop or anything? I get a slight drop right at the very beginning, I thought maybe it was just as the tech said the transition from the idle circuit to the throttle angle circuit..

But like you said I'm measuring the throttle angle circuit, it should measure throttle angle from fully closed to fully open with absolutly no single drop in resitance correct?

I might just see if I can snatch a TPS sensor up and see what happens.

rdharper

When I originally had a concern with my TPS, I bought a salvaged TPS from eBay. From that I realized how it works, not to mention was able to verify my original was identical, and the only problem (in my own case) was a slight misadjustment on the idle switch and a sticking dashpot.

And yes, the angle is like a potentiometer, where the angular displacement is measured by an increase in ohms.... where they very cutely put the 800ohm mark right at 800rpms, and at the transition in the "switch" from idle to "not idle", in the other *parallel* circuit (common return).

Total sweep is about 100degrees... starting at 0 degrees = 50ohms, at 50 degrees, 2750 ohms, and 5500 ohms at full open, aprox 100 degrees. When on your machine, the 800 ohm position would be stopped by the idle stop position, which will be about 15 degrees.

Chuki

so if I read that correctly my TPS has a spot in it not far from idle thats bad, and that could probably be causing my rough idle.



Thanks for the help!