SPARKS89

iTrader: (1)

I replaced the TPS on my truck last night and this morning the throttle acted like it was turning off and on like someone was flipping a switch (needless to say, this is a little more than inconvenient when I'm driving down a busy road).

The new TPS is set to spec, AFM is good, no vacuum leaks and timing and idle speed are set correctly. I know it's something with the engine and not the clutch or transmission slipping (they're both brand new with about 500 miles on them) because I can move the throttle by hand under the hood and it still does it. I can hold the throttle steady for about 30-60 seconds and it will all of a sudden stop doing the on/off mess and run just fine. Does anybody have ANY clue what could be causing this?

SPARKS89

iTrader: (1)

Last night when I first fired it up the idle was surging pretty good but not really high RPMs, but stopped as soon as I plugged in the jumper to check timing and idle speed. Timing was set right at 5* BTDC and idle speed to 750 RPMs. When I removed the jumper it wasn't surging anymore. The idle was VERY smooth after that. The timing backed off to around 8-10* BTDC and idle speed went to around 880 RPMs which I can only guess is normal with the jumper removed.

I also took the truck for a drive last night and everything worked great. No surges or sags in power or any funny business at all. I cleaned the throttle body when I had it off too. Last night during the test drive there was a noticeable difference in power. It definitely had more pep which I was very glad for.

I've been looking through the forums and have found some stuff about the EGR valve being stuck open (I don't think that's the case because it's off and on) or the idle bypass. I don't know what that is. Does anybody have any ideas what could be causing my problem?

SPARKS89

iTrader: (1)

Ok, so I figure I'll keep adding info to this as I get it and maybe it'll help someone else in the future. I can't be the only one having this problem......

I took the afternoon off yesterday to figure out what was wrong with my truck. I checked the AFM, fuel pump, a couple relays among a few other things and everything checked out fine.

I found out that the brand new (not Toyota, but supposedly OEM equivalent) TPS could not be adjusted correctly. I could get all settings within spec but one.....for example: I could get the .57 mm spacer setting to be less than 2.3k Ohm's, but that would throw off my .85 mm spacer setting and vice versa. I could jump the diagnostic ports to set timing and idle speed and the engine would run AWESOME and idle very smoothly once the jumper was removed. The problem showed up when I would hit the throttle. It would reach a point (at a fairly low throttle) that the engine would bogg down. HOWEVER, if i unplug the TPS and open the throttle the problem goes away. The engine definitely runs differently with the sensor unplugged. In fact, it runs just like it did before which proves to me that the old sensor was faulty too. At least I can feel good that I'm definitely replacing a bad part.

What I've learned from this is that my TPS hasn't worked since I bought the truck last December. I've heard that a non-functioning TPS will cause fuel mileage to go down the crapper so I'm excited to see what it will be after I get it repaired CORRECTLY. I'll be ordering a Toyota TPS today.

Good call on using non-OEM parts, Chef. Lesson learned!!!

TNRabbit

Check that there are no breaks/shorts in the wiring harness from the TPS plug to the ECU.

SPARKS89

iTrader: (1)

Thanks Rabbit. I'll double check that just to make sure.

For anyone else that might need it:



It looks a little simpler to follow than others I've seen.

scope103

sparks89 -

That is a good schematic, thanks.

But a little hard to read in the small format (and it only makes me want to see the preceding and following pages). Any chance that's a PDF on the web somewhere?

SPARKS89

iTrader: (1)

I got it off Google images. Just searched '1989 Toyota Pickup Wiring Diagram' and it popped up.

I tried it tho. All you have to do is save it to your computer desktop and print it off. It should print off full-page and it's readable....I have one sitting in front of me right now.

SPARKS89

iTrader: (1)

I checked the wiring for the TPS, coolant temp sensor and AFM this weekend and everything checks out ok.

My new TPS will be in this afternoon so hopefully that will take care of it. Does anybody know how to test the coolant temp sensor? I'd like to test it, just to make sure.

scope103

http://www.ncttora.com/fsm/1990-1995...e/engineco.pdf

SPARKS89

iTrader: (1)

Thanks for the info on that Scope. I haven't had the chance to get into that but I'll post results when I get them.


Ok, so I got the new TPS from Toyota yesterday and here's what i found...

The Toyota OEM sensor is on the right and the fingers inside are a full 90* off of what they should be!!! I called Toyota when I noticed this and the guy verified that it was the right part. Obviously, this isn't going to work.
You can see in this picture that with the sensor on it's side and the plug connector facing the front of the engine the fingers should be vertical (or close to it), not horizontal. So, for the sake of wasting time, I put the other new sensor back on and messed with it. (It's a good thing I put hex-head screws in there last time I had the throttle body off. I'm getting to be a veteran at messing with the TPS). I think I got it set right....everything checked out last night. It looks like I didn't have enough patience with it before. It's such a fine line you have to find when setting the .57mm and .85mm spacer setting. I'm going to check it again this afternoon and see if it's still set right. I still have to have it unplugged though because I'm still having the same problem as I was before. The throttle still seems to have a dead spot in it. After looking at the wiring diagram i saw that the coolant temp sensor is wired in series with the TPS. My thought is if the old TPS was bad (which I verified) then the coolant temp sensor may not be able to send it's info back to the ECU either. I'm going to check the temp sensor this weekend and just leave the TPS unplugged for now. Meanwhile, the Toyota TPS is going back.

I wonder what would happen if I unplug the temp sensor and plug in the TPS......I'm gonna find that out tonight. Post results tomorrow.

scope103

I've never removed a TPS, but doesn't the rotor in the TPS need spring tension to hold it against the throttle extension? So wouldn't you just put a tiny bit of pre-load on the spring in the OEM TPS (turn it with your finger) before you slipped it onto the extension?

If that's correct, it looks like the spring in your old one is worn out, so that you'd never be able to get the idle setting to stay.

Just a thought.

SPARKS89

iTrader: (1)

Both of the sensors sitting there are brand new. You do have to turn the fingers in the TPS just a little to line them up correctly with the fingers on the throttle body itself. But the new sensor from Toyota will have to turn a full 90* before they will line up leaving almost no more play in it to turn with the throttle rotor.

abecedarian

I've come across it where the tabs on the sensor don't match up with the throttle, as in it won't just slip on.

The solution is to rotate the TPS so that the tabs would line up, meaning so the connector end is close to vertical (if not even pointing towards the windscreen) then slide the TPS on, then rotate the TPS connector end towards the radiator.

One sensor is pre-loaded: the one that lines up; one isn't- the one that doesn't line up.

SPARKS89

iTrader: (1)

Right, but when I did that with the Toyota sensor it only had maybe 1/8 inch or so of travel before it reached it's limit. It wouldn't rotate any more than that. I also checked it with a meter while holding it in my hand. When I held it close to where it would be if it were on the TB the readings were nowhere close to what they should be. The aftermarket sensor on the left does have a little preload in it to line up correctly, but not a full 1/4 turn.

SPARKS89

iTrader: (1)

So I'm back again to work on this problem. I've been driving since last summer with my TPS unplugged and other than less-than-desirable gas mileage the truck has been running good. Last night, however, I noticed a funny idle again. This time it's idling around 1300-1400 RPMs. It did it again this morning too. It's not surging or bogging. It's a very consistant idle. I was hoping to get thru the winter and work on getting this problem solved this spring, but no such luck. I want to get the TPS issue taken care of before I start looking at other things. I was thinking a fuel pressure regulator for this latest issue, but I can't be sure unless other things are working right first.

I've tested the TPS and it's within spec. When I put the jumper in the diagnostic plugs the idle changes and it changes when I plug in and unplug the TPS. I've replaced all of my coolant hoses and done a flush a while back and there are no leaks in the system. No bubbles that I know of either so I don't believe it's a problem with IACV. The coolant temp sensor (which appears to be wired in series with the TPS) is good and there's no broken wiring anywhere. I don't have anybody that I can swap ECUs with to see if that's the problem. Is there a test I can do for the ECU?

Every test I've done shows that the TPS and coolant temp sensor are good. I haven't checked fuel pressure (so I can't say for sure about the regulator), but obviously the pump is good. So here's what I have left to test: ECU, fuel pressure regulator and fuel shut-off. Does anybody have any thoughts or suggestions?

BamaYota1

Have you tested the tps circuit at the ecu?

SPARKS89

iTrader: (1)

Checked it last summer. I'll check it again tonight tho.

scope103

If you have had the TPS unplugged, a sudden rise in idle rpm ought not to have anything to do with the TPS. The most likely culprit would be the ECT. My (1994) wiring diagram shows that the TPS and the ECT share the same Brn-Blk wire to ground, but not otherwise (and certainly not in series). What tests did you do on the ECT? http://personal.utulsa.edu/~nathan-b...98engineco.pdf Could you have a broken wire from the ECT to the ECU (THW, B-4, in 1994)?

SPARKS89

iTrader: (1)

I checked the ECT wiring and everything checks out good. My test shows that the coolant temp sensor is good. My check engine light comes on when it's unplugged. I noticed the EGR gas temp sensor also shares this same brown/black wire and has been unplugged, but that is the ground so it shouldn't affect the TPS not working. I'd like to plug it in just to check but I can't find the connection for the life of me! I did find out that the green/yellow wire going to my TPS only has 6 volts. Is this normal or should it be 12?





Can anybody help this little bastard find his home?

Co_94_PU

iTrader: (-1)

Yeah E2 is shared by all(or almost all) the sensors, it actually routes thru the ECU to get that ground to the body.

Can you wipe that off and get the wire colors. It's a semi generic 2wire plug, vac-switch most likely assuming your EGR temp wire is connected.

And after a quick reread of the thread, I see your EGR temp isn't plugged in that's likely it right shape right location. BR-B and G-W are the wire colors. G-W goes to I think pin 13 on the ECU, didn't dig out the other wiring diagrams, it's right next to IDL.

G-Y is VCC should be 4.5-5.5.

My wild guess is... Intake manifold ground strap, clean firm and not overly frayed?