Buick V-6 3.8 Idles Fast in Drive (But idles normally in Neutral)

....86 Buick V-6 (3.8) with 120,000 miles:
idles too fast in "D"rive, BUT idles at normal speed
when put in "N"uetral". TPS (throttle position sensor) had
been replaced previously, and still checks OK with an ohmmeter.
I could not see any obvious vacuum hose leaks. I also had
the battery disconnected for awhile to reset computer.
(still drives at 20 mph with foot off throtlle).
Does this OK-in-Neutral provide a significant clue??
Thanks for any suggestions.

You cannot check the tps with an o'meter, use a voltmeter and set it at dead
idle at .5v. Then go from there.
"Gene Gardner" > wrote in message
...
>
>
> ...86 Buick V-6 (3.8) with 120,000 miles:
> idles too fast in "D"rive, BUT idles at normal speed
> when put in "N"uetral". TPS (throttle position sensor) had
> been replaced previously, and still checks OK with an ohmmeter.
> I could not see any obvious vacuum hose leaks. I also had
> the battery disconnected for awhile to reset computer.
> (still drives at 20 mph with foot off throtlle).
> Does this OK-in-Neutral provide a significant clue??
> Thanks for any suggestions.
>
>



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Gene Gardner wrote:
> ...86 Buick V-6 (3.8) with 120,000 miles:
> idles too fast in "D"rive, BUT idles at normal speed
> when put in "N"uetral". TPS (throttle position sensor) had
> been replaced previously, and still checks OK with an ohmmeter.
> I could not see any obvious vacuum hose leaks. I also had
> the battery disconnected for awhile to reset computer.
> (still drives at 20 mph with foot off throtlle).
> Does this OK-in-Neutral provide a significant clue??
> Thanks for any suggestions.

You may need to give the ECM several days of driving to adjust itself
if you don't closely follow the recommended relearn procedure after
disconnecting the battery and replacing the TPS. You may have a real
problem, but I would give it a few days anyway, then start looking for
problems ie ECM codes, intake manifold vacuum leak, etc. It sounds
like your IAC valve is operational since idle speed tames down in
neutral.

Shep's point is a good one, too. You should make sure the sensor
return wire shows about .5 volts with the key on, engine idling,
throttle closed. There is a small amount of slop in the attachment
screw holes for adjustment.

Toyota MDT in MO