Haynes manual testing Throttle Pos Switch

Richard Foy · 09-25-2001, 04:32 PM

Has anyone figured out what the heck the Haynes manual is trying to say on its testing of the Throtttle switch on page 107, para 16 - 23?

My guess is: the TPS (Throttle Pos. Sw.) has 3 pins 3,13,2. I think the center pin (13) is 'common or ground' and the other two go to the DME telling it IDLE or WOT
Note: Short is zero ohms, OPEN is inf. ohms\

When Throttle Closed (idle)
Between p3<---OPEN--->p13<--SHORT-->p2

When Throttle above idle, below WOT
Between p3<---OPEN--->p13<---OPEN--->p2

When Throttle Wide Open (far above idle)
Between p3<---SHORT--->p13<--OPEN-->p2

My TPS reads ok at idle, but never changes from OPEN between pins 3 and 13 reguardless of throttle position. Is that part of the TPS used (pins 3,13)?

[This message has been edited by Richard Foy (edited 09-25-2001).]

[This message has been edited by Richard Foy (edited 09-25-2001).]

Charles · 09-25-2001, 07:14 PM

Various sources (folks on the 'net, mostly) say that the WOT side of the switch changes the mapping inside the DME. If I recall, the changeover ignores a few of the parameters to force the most performance out of the car.

Your interpretation of the switch contacts appears to be correct. You should hear two clicks when you manually rotate the throttle cam (once when it comes away from the idle screw, and once at WOT).

Side note: I have been seeing an intermittent reduction in wide-open acceleration in my '85 NA, and I haven't had the time to check out the TPS. Given the problems that I've had at idle when the switch malfunctions, I'd say it's a likely suspect in my case.

Hope that helps,

-C

[This message has been edited by Charles (edited 09-25-2001).]

kcturbo · 09-25-2001, 07:49 PM

I take it that this is a N/A car right? Need to make sure that the resistance decreaces with the opening of the throttle and that there is no loss of signal to the DME.

newoldguy · 09-25-2001, 08:28 PM

I've had a starting problem so maybe this is the culprit. I'm sitting here with the Haynes manual and throttle switch in front of me. First of all, I only get one click as the switch leaves idle and no second click at WOT as Charles is suggesting. Secondly, I have no change in ohm reading from pins 3 to 18 and 2 to 18 at WOT (PS - I think its 18 not 13 as the center ground spade). So----is this a problem with "adjustment" ( I really couldn't feel any bottom out on an internal stop) or do I get on the internet again and buy new part?????
Curtis' '87 944 na

Richard Foy · 09-26-2001, 04:07 AM

newOldGuy,
you're right, it is pin 18 not pin 13

--WOT Side-------------|----Idle Side--------
I.
When Throttle Closed (idle)
Between p3<---OPEN--->p18<--SHORT-->p2
Click heard, felt when moving off idle

II.
When Throttle moved above idle, below WOT
Between p3<---OPEN--->p18<---OPEN--->p2
NO CLICK HEARD after moving off idle thru WOT

When Throttle Wide Open (far above idle)
Between p3<---SHORT--->p18<--OPEN-->p2
No click heard or felt when this short occurs

kcturbo - sounds like your talking about the AFM, not the TPS..as far as I know the TPS is either inf or zero resistance between the pins?

Charles · 09-26-2001, 04:28 AM

Quote:

Originally posted by newoldguy:
I've had a starting problem so maybe this is the culprit.

If the starting problem is related, it would most likely be with the idle side of the switch. The other morning it got really cold here in the mountains, and I could get the car to turn over but it wouldn't keep running unless my foot was on the gas pedal. That turned out to be yet another intermittent connection on the TPS (solved by reseating the connector).

The only way the WOT side would affect starting is if the switch is stuck closed. I'm sure the DME is confused if it is simultaneously getting signals for "idle" and "wide open". You said you saw "no change" -- is the WOT side of the switch open or closed?

Quote:

So----is this a problem with "adjustment" ( I really couldn't feel any bottom out on an internal stop) or do I get on the internet again and buy new part?????

The only adjustment I know of is to shift the position of the switch by loosening the mounting screws.

Good luck,

-C

T86951 · 09-26-2001, 01:05 PM

That is the problem I am having. The car starts fine but the colder it is it is harder to keep it running unless my foot is on the gas pedal. The reason is the idle control valve is not getting a signal from the DME to open up. From what I am reading on here this is due to the TPS sending a signal that the throttle is WO rather than at idle. My MPG metter is real low at cold start signifying a lot of fuel coming out of the injectors. That all stops and things get ok once the OS2 sensor warms up and then the MPG meter then goes up to about 35 and the idle is ok.
I sprayed my throttle body with cleaner about a year ago and it started after that. I wonder if the cleaner kills the sensor?

[This message has been edited by T86951 (edited 09-26-2001).]

[This message has been edited by T86951 (edited 09-26-2001).]

T86951 · 09-26-2001, 06:54 PM

I can't hear a click when I work my throttle, I put my ear very close and didn't hear anything.

newoldguy · 09-26-2001, 08:58 PM

After carefully doing the "test" several times, I now believe my sensor is OK. I think I didn't have a good enough connection with my probes when I was checking it last night. Anyway, it does read the way Richard has outlined it. As far as the "click" goes, I was able to "adjust" it away or back in with the two adjustment screws so T86951 you might need to adjust yours. Mine is out of my car so I don't know if that makes a difference or not but the Haynes manual talks about checking both installed and removed. Also, on some of the car shows I've watched on TV they always seem to be careful about taking the electrical stuff off parts before cleaning----but who really knows??? Anyhow, I hope I'm right. Good luck with your rides guys!!

newoldguy · 09-28-2001, 10:05 PM

Just another bit of feedback---I put the throttle body back on my car and with all vacuum lines connected, accelerator cable on, and spring connected, I COULD hear the "click" when the butterfly valve leaves idle. For what its worth.
Curtis

T86951 · 09-30-2001, 12:15 PM

I'm not sure I understand the open and short thing. I'm not very electrical minded. The Haynes manual says the ohm meter should go to 0 ohms with the throttle closed and the leads from the ohm meter connected to pin 2 and a good ground (with it still on the car). My meter does nothing. I can open and close the throttle and it still doesn't go to 0 or even move at all when closed.
I have checked my meter it is ok even tried another meter. My TPS clicks when you open and close it but no ohms!
Can this be adjusted or is my TPS dead?

newoldguy · 09-30-2001, 08:47 PM

T86951---When Richard and I were kicking this stuff around I believe we both have n/a models. His analysis of the relationship between terminals 2,18, and 3 I think pertain to our cars. In your case, with the turbo, it may not apply as the Haynes book seems to imply that there is a different terminal (12) to check. So, I'm not sure if our checklist is the same as yours. I think I'd try to get it out of the car and on the bench so you can insure you''re on the right terminals. In any event, something has to "change" in your readings or it may be TU. Good luck and keep us posted.
Curtis

T86951 · 10-01-2001, 09:59 AM

It is on my NA '86 944 that I drive every day, not my 951.

newoldguy · 10-01-2001, 09:35 PM

OK . Then we're on the same page. I would think that your switch is bad because you should be getting a change in reading when you leave the idle position when you're reading between the center (18) and terminal 2. It should go from a reading of 0 ohms to infinite (basically like you're not connected to anything). Mine would change reading in this mode and now I'm starting again. If you're not getting any change in any reading in any of the positions either at idle or wide open throttle (and if I understand it all!!!) I think its the switch. Hope this is right and you can fix your problem. Damn electronics!
Curtis

T86951 · 10-01-2001, 09:47 PM

Thanks, yes I get no reading at all. I am going to get a new one. My car has 204,000 miles runs good, good oil presure and stuff but switches go bad. I have a cold start problem , rich on start up , MPG gauge is real low and low rough idle but clears up in about 30 seconds. My idle controls valve doesn't open up to let extra air in on cold start like it should but the valve is good. If I put voltage to it straight from the battery it wotks but it is not getting the right voltage from the connector. Maybe a new TPS will correct this problem.

Richard Foy · 10-02-2001, 05:01 PM

I'm back from a trip to Seattle, and am curious to find out how this all works out for you.
I'm putting my engine back together, after replacing all the exhaust valves I bent, when I missed 4th. I testing things, I found my Idle control valve wasn't moving with 12v applied. I opened it up, and found the armatrue inside was all pitted and messed up, and the three 'brushes' were messed up. (944na)