odd idle need help

[Green99GT]

here is the story... when i am in park it idles about 800rpm but when i move the shifter to drive it bogs down and almost stalls and then catches and stays at 600rpm.
it will do the same thing when i a comming to a stop. other then that the car runs great.... any ideas on what could be causing this?

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1999 mustang GT
bone stock (for now)

[DOMIN8R97]

I have a similar problem with my 97 GT. It will lope a bit when it is in park. it goes from 800 rpm to about 1200 rpm and does this like every three seconds. It sometimes also does this when I'am at a stoplight or something and the car will inch up a little bit due to the change in rpm with the brakes on. this goes away after awhile when the car is warmed up. i have heard in MM&FF that there is an idle surge problem with the 94-95 Gt's. This isn't a big problem but can be annoying. does anyone know what is causing our problems???

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Red '97 Mustang GT
Auto
Bone Stock!
(Except for silencer)

The issue with idle surge mentioned in the 5.0 Mustang mag was attributable to problems with the EEC IV which may or may not be applicable to the newer Mustangs since they run the EEC V. It was mentioned in a recent issue (July, Aug 2001) but Im not sure exactly which one. You can check their web site for the technicals.

Given that you are experiencing no "Check Engine" idiot lights, you can assume all the sensors are operating within their stock limits. Id look at the idle bypass valve. On earlier Mustangs, some people have tried drilling small air bleed holes in the throttle butterflies, but I have no information on that procedure past that. So much of the closed loop engine functions are controlled by the engine management computer, its very difficult to troubleshoot idle quality problems without considering that part of the system. Id be tempted to let the deal handle it.

[91LX2Bfast]

Check the MLPS (manual lever positioning sensor?, or something like that, lol.) I know this is something that seems to go bad on Tbirds and causeing surgeing and stalling problems. Since it does that when you are coming to a stop, it sounds like the MLPS may be the problem.
I had a problem where my car was exhibiting similar behavior, but it was because my heater core was leaking, and hot steam was going into my ECU and messing it all up. You may want to make sure thats not a problem either, although you would likely smell antifreeze, and have it on your carpet, and your fluid would be low.

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1997 Thunderbird 4.6L: Dynomax cat-back, MN-12 perf. offroad downtubes and Y-pipe w/ Magnaflow resonator, 80mm MAF with cone filter, B&M trans cooler, Inject-Tech chip, MAC U/D pulleys, KVR front brake upgrade, SVO 70mm TB. 15.2 @ 91 w/ just chip and MAF. 14's next time to the track.

No Longer own: 91 LX 5.0L 5 spd

[Megabyterr]

Originally posted by DOMIN8R97:
I have somewhat of a similar problem too with my 98 GT with a few mods. Mine is a 5 speed and if I rev it in gear with clutch in or out of gear or even just touch the gas pedal it sticks on 1500 to 1200 rpm for almost 15 to 20 seconds before it falls back to idle. There is nothing wrong with cable or manual stop because it springs right back to the idle position yet the rpms stay high. It seems to be getting worse in the fact that sometimes when I come to a stop it will stick at 1500 for over 30 seconds. Doesnt matter whether the car is cold or warmed up. Any advice would be most appreciated.

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1998 Mustang GT 4.6L,K&N filter,Ford racing underdrive pulleys,3.73 gears,and shorty stainless headers. Bassani X pipe with Flowmaster 2 chamber's.