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Old 12-16-2004, 01:25 PM   #1
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Default engine drops to idle when letting off the gas at speed

1988 SE - 3.8, 99,000 miles

When engine warms up some, RPMs will drop to idle speed even at 60+ mph. Engine feels extremely rough, and just barely keeps from dying. No Fault Codes are generated, and this does not happen all the time. No stumbling on takeoff - the car pulls from a stop as though it were new.

Plugs & wires were changed last year, and the EGR (?) valve was replaced 9 months ago. I maintain the car very well.

Might be a dirty IAC?? I am confused since no Codes are being thrown. Any ideas?

Thanks,
Phil C.
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Old 12-16-2004, 03:48 PM   #2
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Is it when the TCC locks up? It could be something wrong in that department.. perhaps?


-justin
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Old 12-16-2004, 05:05 PM   #3
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Quote:
Originally Posted by jr's3800
Sounds almost like the IAC passage needs to be cleaned or you may possibly have a bad IAC... Might be time for a minor throttle body cleaning..
I diagnosed a bad IAC on damemorders car when he came up north this fall. His car would die if it was idling, or was off of it on the freeway. Fixed it for the most part, a bad timing chain isn't helping him though.
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Old 12-16-2004, 10:12 PM   #4
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You mean that while in drive, if you back off it will die ? Have heard of an IAC causing that when coming to a stop but never at 60 mph.

There is a DFCO (decelleration fuel cut off) program in the ECM to keep the rpm up when you back off in drive. Know that it takes a scan tool to check but is there any chance the gear selection connector (tells the ECM what gear you are in) is messed up and it thinks you are in neutral all of the time ?

I would clean the IAC first but if the problem persists, see if you can find a scan tool (OTC 2000 will tell you which gear the ECM is being told it is in).

TCC drops out as soon as the TPS drops under 2.5% (foot off gas) so should not be an issue.
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Old 12-17-2004, 07:22 PM   #5
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Problem resolved.

Turned out to be a shorted IAT sensor. The sensor was replaced, and the Intake was thoroughly cleaned. Now I might be able to squeeze out a couple more miles to the gallon

Thanx to all for the suggestions.

Phil C.
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