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DRIFTINGmy85
10-20-2008, 09:22 PM
I was messing around with my 84 today...
My idle was WAY up there at 1200 and I finally decided to fix it. I thought I had already tightened the air-screw on the throttle body fully CW which made me think that the high idle was because I messing with 2 small adjusting screws on the throttle linkage trying to get smoother throttle operation.

I hooked up an analog voltmeter to the trouble code connector and then shorted the check engine connector so I could verify the timing in conjunction with the idle. I checked the air-screw and it was like 5 turns CCW so I tightened it ALL the way CW. I also adjusted that screw to check if the ISCV (Idle Speed Control Valve) was working properly. If you move that screw to change the idle, within 5 second the Computer should correct the idle using the ISCV. That's 1 way to check the operation of that unit.
No trouble codes are present and the analog voltmeter told me a very interesting story. Something that I've noticed my cars (86 Celica & 85 Supra) doing before. I have mentioned this phenomenon before but no one really knew what I was trying to explain.
I took 3 videos of what I experienced.
(Also when I finally figured out how to adjust the TPS on my 84 I noticed it doing this too but I didn't put it together in my head quite like I did today. It was also going in and out of timing set mode making it a PITA to figure out.)

Basically it's this, if the throttle is not "Snapped" back into place the TPS sits in an open position, open being open-circuit, and the computer is not in communication with the TPS. When putting the feeler gauges in between the throttle and the idle-stop-screw the analog meter would fluctuate like it should but when I removed the feeler gauge the meter would not fluctuate until I pushed the throttle closed. Playing with it a little but I noticed it wouldn't remain fluctuating unless the throttle was pushed back in after revving it.

Today, after tightening the idle-air-screw, the analog meter fluctuating in front of me, and the engine idling I began to adjust the 2 tiny screws on the throttle linkage that is connected to the throttle body. I had to keep pushing the throttle all the way in to keep the circuit working, with the needle fluctuating I adjusted my idle to 750. (Note: Exhaust cam is 1 tooth advanced and the distributor is fully CW and timing sits at 13BTDC.)

I setup the analog meter so I could see it through the crack of the hood and the cowl and sat in the driver's seat to see what happens when I simulate driving and to see if it's like what I've experienced before but couldn't explain why.

I described it before as 'blipping the throttle.' Changing from prolonged cruising speed, like getting off the fwy, after letting off the throttle I would notice my idle to be higher than it should be. Blipping the throttle always got the idle to drop down a few hundred rpms usually back down where it's supposed to be. Sometimes I had a high idle due to other reasons so it would idle higher than the already high idle. Blipping the throttle would then bring the idle down from really high to just high.

http://s18.photobucket.com/albums/b111/Muziq_138/84p%20TPS/?action=view&current=MVI_7302.flv
http://s18.photobucket.com/albums/b111/Muziq_138/84p%20TPS/?action=view&current=MVI_7303.flv
http://s18.photobucket.com/albums/b111/Muziq_138/84p%20TPS/?action=view&current=MVI_7304.flv

After writing this post I might have a valid reason for this phenomenon. Since the TPS sits in the idle position for most of it's life a burn spot or otherwise worn out spot exists in the spot that the throttle rests at when the it is let off and closes. Therefore, blipping it or closing it, moves it past that spot to continuity.

Opening the throttle to notice the analog voltmeter fluctuation getting interupted.
http://i18.photobucket.com/albums/b111/Muziq_138/84p%20TPS/IMG_7301b.jpg

Closing the throttle fully for fluctuation of the voltmeter. The red circles indicate the 2 screws I was adjusting.
http://i18.photobucket.com/albums/b111/Muziq_138/84p%20TPS/IMG_7301.jpg
Dave A.
10-20-2008, 10:10 PM
The stop screw adjustment on the TB is a very precise adjustment. I would double check that first before attempting to adjust or replace the TPS. The online TSRM has all of the specs..
CarFreek
10-20-2008, 10:44 PM
Did you check inside the T/B? The symptoms you describe sound like contamination not allowing throttle plate to close- A known problem with M series engines. The shaft bearings can wear out also, allowing temporary bind.
sowsley
10-20-2008, 11:24 PM
I second checking that the throttle body is really clean. What you describe sounds like something is crudding it up. It's hard to really clean it when it is on the car. Taking it off will give you much better access to all the adjustments and for cleaning. I did mine and learned a lot about function. I'd be careful about adjusting the TPS without reading the TSRM carefully and doing all recommended adjustments and checks first. The gasket is about $2 at Toyota.

Check my post for checking the '82
http://forums.celicasupra.com/showthread.php?t=42768&highlight=hesitation
DRIFTINGmy85
10-20-2008, 11:57 PM
I agree with you guys. It does sound like a gummed up throttle plate.
Watch the videos and tell me what you think.
I think it's more than a gummed up throttle plate though because of the signal on the voltmeter stopping.
Shouldn't the analog voltmeter stay fluctuating the whole time you have the check engine connector shorted and the voltmeter hooked up?
sowsley
10-21-2008, 10:14 AM
The TPS functions like a simple on-off switch. If it is fluctuating, something is wrong and I suspect dirt first, a bad TPS second. You should be able to check full function of the TPS while the throttle body is off the car and fully disconnected from the car electronics. I don't know what scale you are reading resistance at, but I set my multimeter to show a full sweep of the scale between 0 and infinity. Still sounds like a dirty TPS. Take it off the car, clean and adjust to specs then put it back on the car and check for air leaks in the intake system. It's hard to check it properly on the car. By the way, I uploaded a full scale template you can print out to check continuity with the throttle plate open at 61 and 71 degrees. It's a link in my post above.

***EDIT 1/1/09*** The TPS is a little more complicated than a simple on-off switch in that you must check the readings within a very tight range of tolerances both when closed and when the throttle plate is wide open. If your TPS readings are off, I still recommend taking the throttle body with TPS off the car for cleaning and adjustment. If you have a square TPS, download my full scale template you can print out and cut for checking TPS readings at 61 / 71 degrees. (Link in my signature). I recommend using a pair of insulated alligator clips to attach the leads of the multimeter to the TPS pins. It will make your adjustment go faster. END OF EDIT ****
DRIFTINGmy85
10-21-2008, 02:23 PM
Thanks for your input.
I'll check out that link when I get home and inspect it how you're explaining.
The fluctuating I'm talking about is the sweep of the check engine light on the analog meter.

You can't set the timing until the TPS is adjusted properly. My question is, shouldn't the analog meter stay fluctuating if the tps is functioning properly throughout it's range of motion?

If it stops fluctuating at all through it's range of motion does it mean the TPS is not adjusted properly?

(Let me know if I am hard to understand, sometimes I don't explain things how I am thinking it.)
Donn29
10-21-2008, 04:53 PM
My TPS issues were TPS related, I had 2 and the one from my car did NOT fully return, and the return it did was slow. It should be quick to follow the throttle plate.
Also remember that the dashpot will slow the closing of the plate for a few quick seconds.
sowsley
10-21-2008, 05:02 PM
Also remember that the dashpot will slow the closing of the plate for a few quick seconds.

Maybe 2 seconds max. More like 1 second.
StanS
10-22-2008, 01:05 AM
Drifting my 85 posted:
the TPS sits in an open position, open being open-circuit, and the computer is not in communication with the TPS.

As I understand it, when the TPS sits in an open position the ecu interprets this as not being in idle and therefore the ecu does not try to adjust the idle speed via the iscv to idle spec., 650rpm. Therefore, for correct idle speed, the mechanical adjustments must set the tps at idle position during idle. iirc, you can check that the tps is in idle position with an ohmeter.
DRIFTINGmy85
10-22-2008, 01:12 AM
Today, my idle was at 1000 and I couldn't get it to drop using my 'throttle blip.'
I didn't try pushing the linkage shut. We'll see what follows.
Dave A.
10-22-2008, 11:49 AM
Drifting my 85 posted:
the TPS sits in an open position, open being open-circuit, and the computer is not in communication with the TPS.

As I understand it, when the TPS sits in an open position the ecu interprets this as not being in idle and therefore the ecu does not try to adjust the idle speed via the iscv to idle spec., 650rpm. Therefore, for correct idle speed, the mechanical adjustments must set the tps at idle position during idle. iirc, you can check that the tps is in idle position with an ohmeter.



The TPS contacts IDL & E1 should make contact at idle. Very easy to check with an ohmmeter.
Dave A.
10-22-2008, 11:52 AM
Today, my idle was at 1000 and I couldn't get it to drop using my 'throttle blip.'
I didn't try pushing the linkage shut. We'll see what follows.



Sounds like you need to quit fussing with your TB & TPS and just rebuild the TB back to factory specs.. You really shouldn't have to push or blip the throttle closed if the TB & the throttle linkage are in good working order.
DRIFTINGmy85
10-22-2008, 12:28 PM
Sounds like you need to quit fussing with your TB & TPS and just rebuild the TB back to factory specs.. You really shouldn't have to push or blip the throttle closed if the TB & the throttle linkage are in good working order.

I agree.

I'm still stuck on whether or not the check engine light (analog meter) will remain blinking or not.
I heard on the 85/86 the check engine light won't show if the tps is out of adjustment.
I went out to try this on my 85 but I already took the negative clamp.
I'm gonna try this later today.
I'm also going to check continuity the same way when I took the videos.

I need to go to pick a part and pick up a bunch of tps's to disassemble and rebuild for spares. If I could even rebuild them to good working order.
Donn29
10-22-2008, 02:24 PM
I agree.

I'm still stuck on whether or not the check engine light (analog meter) will remain blinking or not.
I heard on the 85/86 the check engine light won't show if the tps is out of adjustment.
I went out to try this on my 85 but I already took the negative clamp.
I'm gonna try this later today.
I'm also going to check continuity the same way when I took the videos.

I need to go to pick a part and pick up a bunch of tps's to disassemble and rebuild for spares. If I could even rebuild them to good working order.

You just can't check for codes or properly set the timing without having IDL and E1 together. You can unplug the TPS and manually short it it help you set the timing or idle properly if your TPS is faulty(not fully returning).

When you pull them just keep the ones that fully return. Not sure if you could get a new spring to make it fully return.
sowsley
10-22-2008, 04:40 PM
I agree.
I need to go to pick a part and pick up a bunch of tps's to disassemble and rebuild for spares. If I could even rebuild them to good working order.

You probably don't need to do any of that. There is really no disassembly. Just take your old one off, clean it and all the orifices well, and check the tolerances between the adjusting screws (I think there are 2), and then the continuity of the TPS against the 61 / 71 degree template. All done off the engine. It isn't rocket science and it doesn't take that long.

I think it sounds mysterious because you are messing with it on the car and with the engine running. Take it off the car and put it on your kitchen table and you will see how simple the whole thing is. The gasket is $2 and it is held on by 4 bolts. All the tests are bench tests. If one fails, then just put it back on the car, drive down the the pick n pull and get a spare to rebuild.

Print out the pages from the TSRM on the throttle body, read it until you understand it, then just do it.
bozosoku
10-22-2008, 05:49 PM
I once had a dashpot that would stuck from time to time, so the throttle plate would open slightly if it is not snapped back quickly or pushed down. Check that too.
Donn29
10-22-2008, 07:06 PM
61 / 71 degree template.

Not sure I've heard of this term before, whats this?
sowsley
10-23-2008, 02:42 AM
Not sure I've heard of this term before, whats this?

It's in the TSRM as a diagram. You scale it up and insert it into the throttle body. It is a guide that helps you open the throttle plate to either 61 degrees or 71 degrees depending on which end you insert. You check continuity of the TPS at each opening position per the TSRM table. I scaled it up full size (link to pdf in my signature) so you can print it out and glue it to some cardboard so you don't have to draw it by hand.

It looks like this:

http://i180.photobucket.com/albums/x305/sowsley/Supra/TPS-61-degree-image.jpg
DRIFTINGmy85
10-23-2008, 09:46 AM
I once had a dashpot that would stuck from time to time, so the throttle plate would open slightly if it is not snapped back quickly or pushed down. Check that too.

This info seems like something that could be contributing to my experiences.
Why does the dashpot have a filter on one end?

This morning my idle was at 1000 and when I pushed the throttle with my finger it dropped to 750. I'm going to rebuild my TB this weekend as per everyones help and direction.

Thanks for the degree diagram. The link in my signature has the specs for 60/70 degree but I was a bit confused on how to achieve exact degree opening.
Dave A.
10-23-2008, 05:11 PM
Why does the dashpot have a filter on one end?


That filter is an air filter that lets filtered outside air into and out of the dashpot diaphragm.
DRIFTINGmy85
10-23-2008, 07:56 PM
That filter is an air filter that lets filtered outside air into and out of the dashpot diaphragm.

Gotcha. ;)
Guess it's just that simple.
Donn29
10-24-2008, 09:23 PM
It's in the TSRM as a diagram. You scale it up and insert it into the throttle body. It is a guide that helps you open the throttle plate to either 61 degrees or 71 degrees depending on which end you insert. You check continuity of the TPS at each opening position per the TSRM table. I scaled it up full size (link to pdf in my signature) so you can print it out and glue it to some cardboard so you don't have to draw it by hand.

It looks like this:

http://i180.photobucket.com/albums/x305/sowsley/Supra/TPS-61-degree-image.jpg

Must only be in the 82 TSRM
Edit: just re read the fine print. Duh..... whoops