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tbirdsc15
04-21-2012, 04:20 PM
This may be normal but im not sure, When I come to a stop light my car idles down to 750 rpm for about three seconds and then it drops to 500 light someone thru a switch. Doesnt seem to bother anything just kinda strange. Idle is set properly, Idle air control valve is working properly, Throtle position senosr has proper voltage at idle. No Vacume leaks, Everything checks out good. Im a Ford tech and have monitered everything while its running with our SBDS tester and cant find any root cause for this, Long and short fuel trims are proper and O2s are new. Cant find anything in the workshop manual about it. Maybe its normall, Thought I would check with some of you guys and see if your SC does this. Thanks for your time, Rob. 1994 SC Auto trans.

flynbrd
04-21-2012, 08:21 PM
This may be normal but im not sure, When I come to a stop light my car idles down to 750 rpm for about three seconds and then it drops to 500 light someone thru a switch. Doesnt seem to bother anything just kinda strange. Idle is set properly, Idle air control valve is working properly, Throtle position senosr has proper voltage at idle. No Vacume leaks, Everything checks out good. Im a Ford tech and have monitered everything while its running with our SBDS tester and cant find any root cause for this, Long and short fuel trims are proper and O2s are new. Cant find anything in the workshop manual about it. Maybe its normall, Thought I would check with some of you guys and see if your SC does this. Thanks for your time, Rob. 1994 SC Auto trans.

Does the SBDS indicate if the ignition module is bad? I had one that would run but would cause problems because of the dwell was shot. The computer controls the idle with timing also.

Smkn600ctd
04-21-2012, 11:12 PM
Mine does that too. But when its at the higher idle, feels like its just a tad bit rough.

Just thought it was the nature of the beast.

decipha
04-21-2012, 11:51 PM
that is known as dashpot, its decaying too fast and causing an rpm drop

if you can log, check out the isckam correction and the idle integrator

nearing the isckam to 0 will likewise cause the intergrator to nearer 0 and may improve dashpot just a tad bit

would be an easy fix if you had some way to change the values in the ecu