Help! RPM's drop when coasting along or coming to a stop.

greendurango · Dec 24, 2006

I'm having a small problem with the D (its a 99 D 5.9 4x4.) What's happening is when I'm coasting along or get ready to stop, the RPM's drop as if it's going to cut out but it doesn't. It happens some of the time but not all of the time. Any idea what it might be or has anyone else experienced this? I've replaced the TPS thinking that might be the problem but that wasn't it. Could it be the IAC?
Thanks for any help. :?

MWeed · Dec 24, 2006

Probably a good time to clean the IAC and the whole throttle body.

greendurango · Dec 24, 2006

The throttle body and IAC were recently cleaned and it helped with idling issues, but I'm still having problems with the RPM's dropping when coasting along or coming to a stop.
Thanks

tomk · Dec 24, 2006

How old is the battery?

greendurango · Dec 24, 2006

It's about 2 months old and is an Optima.

Anyone have any idea what it might be?
Thanks

skitzo.d · Dec 25, 2006

Did you clean the IAC or replace it? Just cleaning it may not be good enough.

greendurango · Dec 25, 2006

I just cleaned the IAC.
Thanks

FSTDANGO3 · Dec 25, 2006

I'd replace the IAC but it may also be a TPS problem. Any codes at all?
Give the TB a good "take apart" cleaning and see what happens.

Steve
DOC Pres

tomk · Dec 25, 2006

I'd give the idle air passages a good on-car soak (engine idling, slowly spray carb cleaner into the passage until the engine stalls, then fill up the passage and let it soak for half an hour.)

I think there was an IAC "lost counts" TSB for some '99s, but I don't think that problem would show up after this long.

?tom

greendurango · Dec 25, 2006

tomk,
What's that TSB "lost counts?" What does that mean? Do you know what the TSB said? Would a new IAC solve this TSB?
Thanks

tomk · Dec 25, 2006

The IAC is a stepper motor and, IIRC, the TSB adds some shielding or something. The "lost counts" cause the PCM to lose track of the IAC position (because it hasn't stepped the number of times the PCM thinks it has.)

Here's the TSB description<ul>TSB #183698 -- Some vehicles may exhibit an idle undershoot or die out during engine starting that may be caused by IAC lost steps. *AK (NHTSA ID #603112, December 18 1998)[/list]but it only seems to apply to starting. Hmm?

skitzo.d · Dec 26, 2006

For me, I'd just replace it.

Help! RPM's drop when coasting along or coming to a stop.

greendurango

MWeed

greendurango

tomk

greendurango

skitzo.d

greendurango

FSTDANGO3

tomk

greendurango

tomk

skitzo.d

Top Contributors this Month

Recommended Communities