TPS Diagnosis

[Hambone]

Just want to make sure I'm on the right track here... First, some background:
I took the car in for an alignment and had them change the oil over to full synthetic with a Wix filter (previously had dino oil and some cheapie filter). As expected, after the change they pulled the EFI fuse and cranked the engine to prime the filter. However after I got the car back, I noticed that it was idling very high - anywhere from 2000 to 2500 RPMs.

I took the car home and checked the codes. It's throwing a 41 (TPS sensor) and a 51 (also TPS sometimes). As I've seen others recommend on here, I started with the lowest code first and tested the TPS according to the TSRM. Everything was in spec except the resistance between IDL and E2 - this always read infinity (no continuity) regardless of the throttle position.

Based on advice I saw JetJock give to TheKnifeArtist in a similar thread the other day, I tried jumpering IDL and E2 and then fired up the engine - in that condition, the idle is within 100-200 RPMs of where it should be, though when I step on the throttle, once it gets to 2500 or so, the engine cuts back to around 500, climbs, and repeats until I let off the throttle. I assume this is expected behaviour since I'm forcing the system to be in idle mode by shorting IDL to E2 - is my thinking correct here?

All this leads me to believe that my TPS is shot and needs to be replaced, but not necessarily. I should note that I haven't taken it off the car nor have I tried to adjust it yet. It turns out I have a spare (tested and functional) TPS left over from the engine swap that I'm going to try out. My only problem now is figuring out how to get to the bottom screw without having to take the whole TB off. There doesn't seem to be enough clearance to even get a right-angle screwdriver in there - well there is, but not to easily get the screw back in Any suggestions for getting to that screw while the TB is still on the engine?

I'm pretty sure that will resolve the code 41 - actually I think I'm going to try hooking up the spare TPS before I even take the old one off t see what results I get. As for the 51 code I'm getting, while I'm sure that's also part of the TPS problem, it could also be related to the fact that for some reason, I don't have a drive belt hooked to my AC compressor - apparently it wasn't on the original engine and the guy I had do the swap didn't put it on the new one either, thinking it was off because of a problem with the AC unit... I suspect that it was because the previous owner was trying to eek out a bit more power (the EGR unit had been replaced by a blockoff plate, the cruise control actuator and vacuum pump have been taken out, etc. etc.)

One thing at a time though I guess Am I going about things the right way? Is there anything I should do or not do before I try swapping the TPS?

Thanks guys!

 

[jetjock]

Yes, you're going about it the right way. The 51 is because IDL and E2 are open. They need to be closed when the throttle is closed so that the ECU will enable the idle speed control system, among other things. The code 41 is cause by the other part of the TPS, the part that reports throttle angle. Suggest you ohm that section out per the manual. The AC belt being off is unrelated. Just be sure the AC button isn't pressed because it too will generate a 51 when the compressor clutch in energized. That will happen belt or or off, engine running or not.

The behavior you're seeing with IDL and E2 jumpered is normal. It's called rpm cut and is the ECU's way of testing injection cut on deceleration. The code 51 should be gone with the pins jumped though. Can't help much on the bottom screw. I know it's a bear. Some people remove the ISCV. Myself, I usually pull the TB altogether for setting the TPS. That way I can set the throttle stop and also thoroughly clean the TB. Finally, whenever power to the ECU is interrupted the learned idle values are lost and will need to be recalculated. Doesn't take long for the box to do it.

 

[Hambone]

Yes, you're going about it the right way. The 51 is because IDL and E2 are open. They need to be closed when the throttle is closed so that the ECU will enable the idle speed control system, among other things. The code 41 is cause by the other part of the TPS, the part that reports throttle angle. Suggest you ohm that section out per the manual. The AC belt being off is unrelated. Just be sure the AC button isn't pressed because it too will generate a 51 when the compressor clutch in energized. That will happen belt or or off, engine running or not.

The behavior you're seeing with IDL and E2 jumpered is normal. It's called rpm cut and is the ECU's way of testing injection cut on deceleration. The code 51 should be gone with the pins jumped though. Can't help much on the bottom screw. I know it's a bear. Some people remove the ISCV. Myself, I usually pull the TB altogether for setting the TPS. That way I can set the throttle stop and also thoroughly clean the TB. Finally, whenever power to the ECU is interrupted the learned idle values are lost and will need to be recalculated. Doesn't take long for the box to do it.

Thanks JetJock, it's good to know I'm understanding things correctly. I tested the throttle angle section again as you suggested, but it tested fine, at least on my Shit-O-Matic meter

As another test, I cleared the codes on the car, then unplugged the TPS on the TB and plugged in the spare instead, then started the engine. Voila! It idled correctly. Now to fight with doing the swap... I know I really should pull the whole TB and clean it up and whatnot, but that's a bigger project than I want to tackle at the moment considering this is the closest I've come to engine work ever (yes, I'm a total n00b, but working hard to change that! )

Anyway, you mentioned that some people pull the ISCV. That's the piece connected to the intake manifold that's blocking the bottom screw on the TPS, right? If so, can I just unscrew the black piece that the wiring hooks into and move it out of the way, or do I have to take off the other part that actually hooks to the manifold and has a gasket? Just trying not to add to the list of problems is all...

Thanks for your input JetJock - I owe ya a beer

 

[jetjock]

Yep, that's the Idle Speed Control valve. It could probably use a cleaning too. You have to pull the entire thing. Two bolts. If you pull it be sure not to lose the boost check valve in the manifold. Seems they can fall out unnoticed as I've worked on cars where they were MIA.

Pulling the TB is a pain if you still have the coolant lines but the ISCV isn't too bad. I'd do that and leave the TB alone. Shoot some cleaner in the PCV port and the two small ports on the top though. When you have the 3000 pipe off you can eyeball the interior and see how bad it is. Open the throttle plate and eyeball the cold start injector too.

 

[Hambone]

Yep, that's the Idle Speed Control valve. It could probably use a cleaning too. You have to pull the entire thing. Two bolts. If you pull it be sure not to lose the boost check valve in the manifold. Seems they can fall out unnoticed as I've worked on cars where they were MIA.

Pulling the TB is a pain if you still have the coolant lines but the ISCV isn't too bad. I'd do that and leave the TB alone. Shoot some cleaner in the PCV port and the two small ports on the top though. When you have the 3000 pipe off you can eyeball the interior and see how bad it is. Open the throttle plate and eyeball the cold start injector too.

Ok that's kinda what I had thought. If the gasket between the ISCV and the manifold is in good shape, can it be reused, or should it be replaced?

Also, the PCV valve and ports you mentioned are on the TB, not the ISCV, correct?

 

[jetjock]

Yeah, the ports are on the TB. Big one on the side, two small ones on the top. That's assuming you still have the factory emissions gear in use.

ISCV gasket can be reused but it's of good practice to replace any gasket. You don't need a Toyota part, just buy a sheet of gasket material at the parts store and make your own. Your call though. Don't be reefing on those bolts either. After you get the TPS back on you can cal it using feelers or simply turn it to where there is no code 51 when the throttle is closed and a 51 when it's just cracked. Of course, the first step is to be sure the throttle is closed ie; no binding and stop screw correctly set.

The accuracy of the when the IDL contact opens and closes is nowhere near as critical as people think. I've never gone into the details behind all the feeler gage BS and I'm not about to now. As long as the other part of the TPS is functioning it's only important the IDL contact closes when the throttle is closed and opens when it's cracked. In reality there is very little need to set it as carefully as the manual calls for and not doing so won't cause a perceptible change in how the engine runs.

 

[Hambone]

As far as I know, the emissions gear is in use, but I could be wrong. The big port is the one that hooks up to the 3000 pipe, and the right-angle smaller one at the back of the TB goes to the air cleaner, right? Is there supposed to be anything connected to the front straight port on the top? On the TB from my old engine, there is a rubber plug in that port - on the current TB, the port isn't connected to anything, nor is it plugged. Unless, that is, you count what appears to be a dead bug coccooned that half-closes the port (don't worry, that's coming out ). Anyway, is there supposed to be something hooked up there?

Wonderful advice about the gasket - I didn't know you could "roll your own", but I'll definitely do that instead of reusing the old one.

Finally, when adjusting the TPS, will the code 51 clear itself once it gets into spec, or do I have to clear the codes in between each check? I've been clearing the codes between each thing that I've tried, but if I can get away without doing so, that would be cool also...

 

[jetjock]

All this stuff is already on the forum so you might want to search. For example code 51 has been brought up often. Too often. Also if you don't have a service manual you need to get one.

The big port on the rear of the TB should connect to the valve covers. The others are the small ones on top. One should go to the EGR system and the other should go to a gadget on the thermostat housing. The small ones are for emissions and you can get away without them but the big one is a PCV port and must be connected or you'll have problems. Pull all three hoses off and shoot cleaner in the TB, not the hoses.

Making gaskets in seconds is easy once you learn how but I'll cover the technique another time. For now just do it the hard way and trace them with a pencil then cut. They don't have to be pretty.

There isn't a need to clear code 51 because it's a "real time" code. It's not stored in memory and will disappear whenever the condition causing it is corrected. It's the only code that does this. You'll need to clear other codes after making repair attempts to get rid of them.

 

[Alang]

Any issues with using the generic gasket material to make my own TB to Manifold gasket?

 

[Hambone]

Well I tried like hell to get a wrench down into the space to be able to remove the ISCV and just couldn't do it, so I finally gave in and took it to my mechanic to let him do it

Turns out the TPS was ok after all. The throttle stop was out of adjustment as was the TPS itself, resulting in the idle sensor always being open. He was able to get everything readjusted (and corrected the timing after the fact as well) and now she's running like a champ.

Thanks again for your help JetJock - and in the future if I feel adventurous enough to try working on my own car again (only about 50% likely ) I'll make sure to do more in-depth research before posting

 

[wanaturbo]

hey would this jumping the IDL and E2 work it the codeis for the CPS also? thanks

 

[jetjock]

Hambone: Glad you got it straightened out. Yes, the throttle must be fully closed as a prerequisite to setting the TPS. The order of adjustment is 1) Verify/adjust throttle linkage as needed, 2) Set the throttle stop screw, 3) Set the TPS, 4) Set the dashpot.

While it's true you should've searched it's also true your original post was the kind people who're here to help like to see. Although I have several criterion a post must meet before I respond I've often cut people slack. My latest policy is zero tolerance. Either a post meets them or doesn't. Had I been operating in that mode yours still would've easily qualified. Looked at from that viewpoint it was refreshing.

Alang: The TB is one of those applications that's perfect for a roll your own gasket.

wanaturbo: Nein.

 

[Hambone]

Yeah I guess I jumped the gun a little bit in my diagnosis... being an electronics guy and given the other weirdnesses the car exhibits (tail sensor comes on randomly for no reason, interior lights only work about 1/2 of time, the start position on the ignition fails sporadically requiring use of a hardwired started switch, etc.), I just automatically assumed that the problem was electronic in nature and never even thought to check the basic stuff first.

Live and learn... at least that's one question I won't need to ask again in the future Thanks for the kind words by the way!