Hi. I have 98 Stang GT, standard trans. Recently I've noticed(when engine is in N) after I give some gas, RPMs go up and then drop down fast to less then 500 and the engine almost stalls, and then goes back up to 800- 900 RPMs.Do you know what could be the problem? Thanks a lot.

 

Is the check engine light on?

 

No its not "ON". and I noticed that it happens only when the engine is warm. In the morning when I start it the first time everything is ok.

Thanks for replying.

 

You should probably start by cleaning out your iac valve really well and also cleaning your maf sensor.. Also you may have a small intake leak coming from a leaking intake gasket.. When the car is idleing at operating temp spray some brake or carb clean all around the intake. If the engine stalls down at any point then you found a leak.

 

Yep, cleaning iac, maf etc is a very good idea, as well as the brake cleaner trick. If that doesn't work, look up in a manual what the resistance/voltage of some sensors are and test them, tps, ect, o2 etc. A bad voltage reading ofless than avolt can throw off the tuning like that

 

Thanks a lot for advice guys. I will try that.

 

+1 on Cleaning the IAC

Before the engine swap in my wifes 96' it had idle problems and even died in traffic and didnt want to start again after that.

That happened to be the first thing that I addressed and I cleaned it with carb cleaner and put it back on, no problems ever since!


-Eric-

 

YOur decay is off.... Could be your IAC, TPS, or a clogged Cat, vacum leak.

 

I'd look for an intake leak too.
When the engine is cold everything is sealed tight.
When it warms up, things expand and may warp out of line a little.
Try checking the torque on your intake bolts 1st.