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Hi all,
I've been unable to get my idle control motor to turn on. Per Bentley, I tested @ #2, which should show continuity to ground at idle position (which should energize the idle control motor, yes?). No dice. So I replaced the TPS. Still no continuity to ground. Should I assume that the new TPS is bad out of the box? Or is there some other cause for this?
In the meantime, am I causing any harm by adjusting the throttle valve to crack open and provide some idle?
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Well, late yesterday, the ECU began returning multiple error codes, and would not reset.
I pulled the original 561 ECU and installed my spare 951 ECU. All seems well now. No error codes. Nice idle, so I have to assume the TPS and idle control motor are working.
Thanks to all for their input.
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Disconnect the throttle linkage arm from the throttle body. If the TPS closes now adjust the linkage so it is closed when it is attached. Dan
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I've done this. With the throttle linkage disconnected, I loosened the two adjusting screws on the TPS. Then, I attached a test lead to #2. I was unable to find any position where the circuit closed and #2 showed continuity to ground.
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Did you install and adjust using the FAQs?
http://www.brickboard.com/FAQ/700-900/EngineSensors.htm#ThrottlePositionSwitch
Take the TPS off and check continuity to see if it is good, it is not common for these to be bad.
Dan
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The mystery deepens. Next, I:
- unplugged the TPS. Idled fine, no change;
- disconnected the throttle linkage and backed off the throttle stop screw. Idled fine, no change;
- unplugged the MAF. Idled fine, no change!!!
Is it possible I'm running around (for some time now) with a bad MAF (running in "drive home mode"), and for whatever reason the ECU has never returned a fault code?
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And let me add: the car runs well, start instantly, cruises at 80mph with no problem.
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You didn't happen to mix the plugs for the TPS and IAC Valve did you? I'm not sure if thats possible, but I think it might fry the switch, and it would explain why the IAC Valve isn't pulsing. It's best to adjust the TPS off the car with a set of feeler gauges available.
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"You didn't happen to mix the plugs for the TPS and IAC Valve did you? I'm not sure if thats possible"
It's unpossible.
The Bentley procedure for adjusting the TPS doesn't use feeler gauges. The main thing is: closed at idle, open just above idle.
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I put a note in my Bentley that you won't get any continuity from terminal 2 to ground in Step 3 because the connector was unplugged in Step 2.
The path from terminal 2 to ground requires internal contact with terminal #18, then out the black wire to ground (on the throttle pulley bracket, I think). I don't believe that's possible, with the harness plug disconnected.
I use a spare JY plug with the 3 wires labeled so I can use my DVM to check #2 and #18 for continuity.
--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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Thanks, Bruce, although I respectfully disagree. The TPS ought to be operational regardless of whether it's connected to the system.
I dunno. I'm flummoxed. And now, to add to the fun, I DO have a check engine light. It's returning a couple of codes, and cannot be reset.
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Hi there,
That you mention a check engine light, I can assume your car is 89-93. It may be easier for you to check that throttle switch operation from inside the car at the ECU plug, pin 2 and ground. Bentley describes the test correctly on p. 241-14, however mistaken they are on p. 241-19. I know us folks more northerly than your warm locale would appreciate being able to check this out from the inside.
--
Art Benstein near Baltimore
Acupuncture is a jab well done.
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Art,
My car is a '90 240, but the ECU test socket is on the drivers side fender wall.
In my Bentley, the test on 241-14 and 241-19 are consistent. Maybe Bentley corrected that mistake in the latest edition?
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Doug, the Bentley is in error on 241-19 in exactly the way Lucid points out. The OBD test socket you mention is not what Bentley is asking you to check on 241-14. To my knowledge, there's only one edition of Bentley, but as most of us know, it would be really helpful if they did a second.
--
Art Benstein near Baltimore
Most would rather be ruined by praise than saved by criticism.
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"The TPS ought to be operational regardless of whether it's connected to the system."
That's right, but the Bentley is telling you to check for continuity from terminal #2 to ground — but the path to that ground is via TPS terminal #18, the (connected) plug, and then to the grounding point.
With that plug disconnected (Step 2), there is no complete ground circuit to test. You are measuring from #2 to nowhere. The TPS part of the ground path is between terminals 2 and 18, at the switch.
You need to do all your testing at the TPS terminals (very awkward) or by using a spare plug and wires.
--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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"With that plug disconnected (Step 2), there is no complete ground circuit to test. You are measuring from #2 to nowhere. The TPS part of the ground path is between terminals 2 and 18, at the switch."
Bruce,
What your are saying makes sense to me ...
In the Green Book the test at the ECU is to ground either of the outside terminals (also avoiding #18 - the middle contact). Is there supposed to be a ground to ground continuity through the body of the car?
Do you think the Green Book is where Bentley got their information ... so they are both wrong?
-------
'88 244 DL, LH-2.2, B230F
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"You need to do all your testing at the TPS terminals (very awkward) or by using a spare plug and wires."
I am. I tested #2 on the TPS to ground; no good. I also tested between #2 and #18, which should also show continuity to ground; nada.
The larger mystery is why disconnecting the MAF has no impact on how it runs.
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