I got my car about a month ago and noticed that after being driven for a while and getting nice and hot when i stop at a light and have to wait for anymore than like 5-10 seconds the car's idle gets real low(500 rpm's), shudders and then shoots back up to 1500-2000rpm's and i have to push pretty hard on the brake pedal to keep it from jumping forward. I just had the heads, and opti replaced but this was happening before to so i dont think they are related. any ideas?

 

meant to add that it only does this when it is in gear (R,N,OD,D,2) does not do it in park.

 

so i guess nobody has any ideas? i guess ill just take it to a shop and have them look at it. thanks anyway, but if anybody reads this and thinks they might know what it might be, your advice would be much appreciated.

 

Check for vacuum leaks or anything obviously disconnected around the intake or intake manifold. Like your intake elbow for example. If its all good then check your throttle body sensors (tps, iac) and maybe your temp sensor on the water pump. Is the ses light on?

 

No, theres no lights on, but i will check that stuff out thanks for your help.

 

If u figure anything out plz post...
I've had this problem before in my 94z. Only happened two or three occasions, all of which I had been driving for about 45 minutes already and was sitting in traffic in weather above 80 degrees. Seems like the heat managed to bring it on as I havent had it happen anytime else.
Although I dont remember my car dropping rpms at all first... it just seemed to rev up on its own, I believe i hit 1600-1700

Edit: Just read your sig.. I'm also driving a 94 Z A4 Conv... all stock though. I also had no work done to car anytime around when it happened.

 

my v6 does it when a vac tube pops off the top of the motor... doubt its the same as the lt1, but i dunno

check for loose hoses...

cory

 

What happens when you guys drive your car. Does it hesitate or buck when you try to accelerate?

 

thats a big negative, my car runs like new its just when its been running for a while it starts to do it. i looked for any tubes that were miss placed but i couldnt find any. i dont know. im thinking it may be the TPS but i could be wrong. im gonna have it looked at at somepoint soon. im gonna keep looking for hoses though ill let you know.

 

I have the same problem, but you can hear a faint hiss. Someone told me it may possibly be the EGR? I also haven't noticed any vacuum leaks..

 

i have a similar situation. mine does buck when you accelerate at a very light throttle. i know my intake elbow in torn where it connects, but i thought i got it good enough to make it work. ????

 

anybody else have anything more to add?

 

A torn elbow is a problem. The water pumps temp sensor will make your car ride like a horse if its bad...

 

I had never taken the elbow off to look at it myself (just got the car about a month ago). I took it off and sure enough there were 2-3 large tears in the lip that meets the intake manifold. guess that could very well be my problem. im gonna get one from slp or maybe somewhere else and see if that takes care of my problem. thank you and i will let you know what happens.

 

Mine was doing that loast night. Happened to me because I had the throttle screw open way to far trying to adjust the iac's.