Throttle Closed Switch

[Superman]

There is a little switch under the cruise control bracket that is supposed to be closed by the throttle linkage when the throttle is returned to idle. Question: What does this switch do? Follow-up Question: If it has to do with CIS, then have I already defeated the switch by unplugging my O2 sensor?

The switch in fact does not get closed by my throttle linkage. The linkage does not return far enough. The switch position does not seem adjustable. Question: Can I assume that my throttle return stop should be adjusted to return a little further so that the throttle linkage moves far enough to close this switch? Follow-up Question: Is it just possible that my throttle does not close all the way? It seems to me that I have adjusted my idle air bypass screw all the way closed and the car was still able to idle. Does this mean my throttle plate is not closing?

[surflvr911sc]

There is a procedure in the Bentley’s manual on adjust the switch. I had to adjust mine when I adjust my throttle b/c it wasn’t opening all the way. I’m not sure exactly what it’s tied into. I know what it’s for but not how it works. I too have disconnected my O2 sensor so I’m curious to find out if it even matters any more. I think it still does b/c the “small” CIS brain still works even when the o2 sensor is disconnected, I think?

OK, I don’t really know much, but I do know you can adjust it. You maybe out of the adjustment limit if your throttle is not completely closing though.

[Superman]

Yeah, I hesitate to adjust the throttle stop because it should never need adjusting. The lock nut is painted.

I also have found that my throttle is not opening all the way. I did some adjusting and got it to open further, but it still does not open all the way to the stop. I think the little bit of extra travel I gave it might have made a difference in power. Maybe. I'm not going to tell my autocross competitors about this.

One more thing. The throttle linkage finger that touches this switch is moved by the throttle linkage but is not fastened to it solidly. It wiggles a little.

[surflvr911sc]

I just had a scary experience. I was test-driving the car on the freeway when I went to down shift the Tach redlined as soon as I pushed in the clutch. Holy $hit! Let the clutch back out, took the next exit and shut down the car. The cruise control cable had gotten hung up. The cheap plastic connectors have not been in the best of shape for quite some time and with the messing I’ve been doing in the engine compartment lately they were knocked just enough to hang up at WOT. No signs of damage, the motor seems fine and is running good.

While I was “fixing” it when I got back home, I started thinking of your problem. If I adjust my CC cable to tight it will not allow the throttle to fully close. Even if it’s close just the cable moving around will cause it to click on and off. Just something to think about if you haven’t already checked it out. Maybe try disconnecting it and see where the throttle sits.

[Superman]

Thanks, Doctor. I used to have a handing throttle issue too, but now I don't remember what part of that mechanism was getting hung up. Mercifully it was not at WOT, but rather at a place where it would hang at 3000 rpm. I fixed it, though.

I know what you mean about the cruise, but that's never the problem. It is adjusted so that there is plenty of slack. the CC system never gets in the way.

[surflvr911sc]

It might not of been completely WOT but it was pretty far up there. All I can say is I now love my rev limiter!

As far as slack goes, on mine, it really depends on which side of the adjustment bracket the slack is on. On the side it should be, the throttle side, it's fine. On the cable side, because of the bad connectors, my throttle jumps a lot. I think I have it fixed though. If it ever happens again it's getting replaced or ripped out.

[Fosgate911]

surflvr911sc

I had the same problem the other day I pinched the bracket that the cable is housed in together a little bit and used some epoxy to keep it in place. BTW it scared the hell out of me as it happened on main street and I had to push it thru an intersection.

T

[Botman]

Man of Steel...

Does your car want to "die" when off throttle and under braking?
Do your revs dip under your normal idle speed? If so check out this thread.

I realize you have CIS and I have DME, but I bet the micro-switch is telling both systems that the car is "off throttle" and taking over engine management by using the "idle settings".

I noticed the above behavior more during cool/cold weather and came to realize that the throttle linkage itself was temperature sensitive and that it would contract just enough to rest on the switch without depressing it. After "tweaking" the linkage a little to ensure the switch was activated when at rest, my problem was solved. BTW- Thanks to ChrisBennet for the original diagnosis.

Don't know the answer to your follow ups, but maybe this can point you in a direction.

Good Luck.

[Superman]

Thanks, Botman. Indeed, my idle does seem to want to drop to 200 rpms when the throttle is closed quickly. I'll file that away for future reference. I don't think there are many similarities between our fuel systems, and with my O2 sensor unplugged, my system should work pretty much like a K-Basic CIS (no computer), so I am not really thinking that this switch has any current effect on the engine. Also, in the parking lot today I revved the engine and then released the throttle and manually triggered the switch. It seemed to still suffer from the too-low idle drop problem. Not sure, though. Inconclusive. I'll do more testing. In the meantime, I'm waiting to hear from one of those guys that really do understand these things perfectly.

[Doug Zielke]

Bentley sez:
" The 15 degree throttle switch ('81-'83 CIS) provides a 15 degree throttle angle input to the oxygen sensor control unit. When the engine is cold, this switch signals for momentary enrichment (75% duty cycle for 2 seconds) when the throttle moves past 15 degrees."

So, it sounds like a disconnected O2 sensor don't need no stinkin' throttle switch.