When in drive my car idles at about 650rpm, but for the past week or so while in drive idleing rpm's are jumping around between 400 and 600ish and sometimes dropping down as much as 300. I thought I had a bad EGR valve so I replaced it with a new one and it is still doing it. When this dip occurs my A/F ratio guage drops all the way to lean then comes back up with the idle. Does anyone have any thoughts on what is causing this?

Thanks David

 

I am no expert on this by no means but allot of the time i hear this.Most say o2`s are the cause. and most didn`t have ses light to show the problem, I don`t know just my .02 cents worth. Good Luck. Mike...

 

I agree. Try disconnecting the O2 sensors and see what results you get.