Another exciting throttle linkage thread! Yay!

[usurpah]

Hi friends,
I've read about 2,000 throttle linkage threads, but unable to find one with the symptoms I'm seeing. I was wondering if anyone could help. Here's what is going on:

Car: 1988 911 Carrera, 100k miles. Stock w/ Steve Wong chip.

• When the engine is cold, the throttle will act fine, no misbehaving.
• After the car gets to operating temperature, the engine will 'hover' at around 2,000 rpm - either from lower or higher rpms. When the car is at idle, I've seen the revs climb to 2,000 without any input on the pedal.
• If I pull up on the pedal, the revs will fall to idle.
• The linkage on the transmission has been lubed and feels pretty smooth and clean.
• The cruise control cable has been removed from the throttle body - only linkage is from the pedal cluster/
• The springs on the throttle body are strong - the throttle snaps to close when released by hand.
• Pedal cluster has -not- been rebuilt
  
  And here is what's weird:
  
• If I let the car hover at 2,000 rpm, get out, go to the engine and pull up on the throttle lever, it has no effect - it's at the bottom of it's travel. I cannot return the car to idle from the engine compartment.
• Going back to the car and pulling up on the pedal returns the car to idle.

Okay, what gives? Should I rebuild the cluster and hope for the best? I still don't understand how pulling up on the throttle from the engine compartment would not return the car to idle.

Thanks for any ideas!

[on-ramp]

Originally posted by usurpah
[
And here is what's weird:
[*]If I let the car hover at 2,000 rpm, get out, go to the engine and pull up on the throttle lever, it has no effect - it's at the bottom of it's travel. I cannot return the car to idle from the engine compartment.
[/B]

i suspect it's something else rather than your accelerator linkage parts.

[porsche356a]

Hi -

Check your micro idle switch for continuity/adjustment.

It is the smaller switch located on the throttle body housing.

Sorry, I don't have a picture handy.

[usurpah]

Originally posted by porsche356a
Hi -

Check your micro idle switch for continuity/adjustment.

It is the smaller switch located on the throttle body housing.

Sorry, I don't have a picture handy.

Hmmm, did a search for "idle switch" and found this thread:

News Flash... Fellow Pelican solves hanging idle mystery!!!

Which looks pretty similar to my problems! I'm going to check it out now. Thanks for the lead.

[Oldporsche]

Try for a vacuum leak at "operating temperatures".

This is where the efi guys need to chime in.

david Duffield

[usurpah]

Okay, just got done with fiddling with this a little.

It looks like my idle switch sender(?) is bad. I tighted up the return spring on the throttle (shortened the spring). I also tested the idle switch by hooking up a meter and I could tell that something was happening when I pushed on the throttle - it showed some movement on the meter. I could also hear the switch "click" at just the right moment - every time I moved the throttle, the return spring would easily apply enough pressure for me to hear the "click".

I took the car out and it felt a little better, but again after warming up, the idle would hang at 2k.

I got out and pushed hard on the throttle from the engine compartment and the revs dropped to idle instantly. Tried it again, and same thing. It looks like when I push the throttle level in hard, the switch is engaged further and the car drops to idle. So even though the switch is 'clicking', it's not sending that signal to the DME until I -really- push it.

I have a couple questions:

1) Even with the idle switch not fully pushed, the throttle is CLOSED. There's very very little movement to close that switch fully (about 1mm or less). Why would the car hang at 1500-2000 rpm with a closed throttle even if the "idle" switch wasn't closed. Doesn't that seem weird?

2) Is it common for these switches to fail? When I had the car off, I ran my finger over the top of that switch and things were pretty dirty. I can imagine that it's full of dirt and not making a complete contact.

3) This looks like a b*tch to replace! Time for the shop?

Thanks everyone!

[Yellowbird RS]

Check your Lamda sensor.

[Steve W]

Sometimes when the throttle linkage slack is taken up from between the linkage between the tranny pivot and throttle body, and too much slack is taken up, it will cause the throttle butterfly to close the microswitch intermittently, thereby causing the intermittent hanging idle. Make sure there is enough slack in the linkage here to allow the switch to close, and often throttle slack preventing wide open throttle switch engagement should be taken up on the linkage between the gas pedal and the tranny pivot. You an see the idle microswitch at the end of the pen tip. The little red button is the switch, and you can see the acutator arm that is supposed to activate it.

[usurpah]

Thanks for the replies, guys.

Steve: the picture made things clearer, thank you. I double checked the clearance of the idle switch sensor and it seemed fine. I also double checked the length/play in the linkage between the pivot and the throttle body - there was some play in the linkage (didn't feel too taught to cause this).

I had to take the car in for state inspection, so I'm going to let my shop take a peek and see what they say.

I'll post results here so this can help someone in the future.