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Discussion Starter #1
LONG story, here is the shortest possible version:
It has had serious idle/throttle issues (like dangerously high throttle that will not go down as if accelerator cable is stuck.) It was intermittent but began happening more and more, Have replaced:
  • idle engine control valve, (which mainly fixed it)
  • mech disconnected cruise control cable
  • now changing out throttle bodies.
The transmission seems to lag shifting into the next gear at any speed. Lettng my foot off the gas allows it to shift. It's not the transm. (rebuilt and @ 90,000) it is smooth as ever.
The other suspect symptom is throttle response to the brake. The engine lags when stopping. It's not as bad as it first was but the engine won't go below 1000 rpm until the brake has been applied for a few seconds or I tap it. Sitting at a light, the idle goes back up on its own. if I tap the brake while still stopped I can get the idle to respond and go back down.
Also, turning on AC will add work load to engine and make idle go down.
I am thinking there is some computer/electrical problem that needs to be diagnosed.
CEL has been on but that is for a downstream O2.
ABS light has been on but we changed speed sensors. That fixed another transmission issue, but ABS remains on.
That's all I got. I want to run this car another 250k!
 

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What year, which engine?

Just a wild guess, but I think a TPS (Throttle Position Sensor) can cause these symptoms. It might just need adjusting so the "throttle is closed" switch goes closed when it should, which is slightly before the linkage hits the stop. Or it could be glitchy, where the resistance doesn't change smoothly through the throttle's stroke. If there are any jumps in resistance, it can cause the ECU to do all sorts of wonky things.,
 

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Whups, I missed that! Thx!

With that info, my suggestion regarding the TPS is valid. I think sometime in the later years, they did away with the "throttle is closed" feature in the TPS?

Here's a link to an Autozone page showing how to check/adjust it.
 

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Discussion Starter #5
from my other post in another thread, this sounds like a promising answer:
The "lag" on upshift sounds like a misadjusted kickdown cable, the "lag" on braking could be a small to medium vacuum leak, or some problem with the rebuild.

We've done everything else, incl. the TPS. We have not looked at the "kickdown cable", and not sure about the vacuum leaks. The transmission rebuild was many years ago, so again I don't suspect that.
I will report back!
and thank you for the answers!!!
 

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Discussion Starter #6
OK, they still haven't figured it out, but given that they've reset the computer (pulled fuse) to try and get an error code, we believe there is something going on with the computer even thought it is not showing up as a bad computer. Again the two main symptoms remain the same- idle will not stay down when fully stopped and shifting lags at any speed when accelerating. (note they have fully sprayed/tested all engine lines- no vacuum leaks) Nevertheless, I love my mechanic as he seems to have gotten caught up in my spirit to keep this baby on the road! He has complimented me previously on the relative youth and power of the V6 engine! :)
Will report back in a week or so.
 

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Discussion Starter #7
We still haven't figured it out, but I have noticed that when it it's cold there's no apparent problem. Only when engine has had time to warm up does it begin to happen.
Drove it 400 miles this past weekend and another 50 today. Weekend trip was no problem- all highway driving. It only began to "act up" again at the very end of my trip today, which ended with a lot of start/stop in city traffic.
So there's more clues....
 

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This may sound odd, but how is your fuel system? When it lags to shift, what are your RPMs doing? Do they slowly float down or do they drop like normal?
 
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