RPM dip while in neutral?
 

Ok after 3 years of ownership Ive finally made a thread about my RPM's that dip once i put the car in neutral at stop lights.

heres the situation:

car is at normal operating temps. AC is on but not blasting. Weather outside is hot and humid. im driving along like normal and come up to a stop light. i stop at the light and put the car in neutral while i wait for the light to change. as im waiting there my RPM's will dip from the normal 750 to just under 500 and go right back to 750.......

is this normal?

ive recently had my fuel pump changed out after it quit working on me a few months ago. the dipping RPM's happened before and after the fuel pump change so i dont believe it is fuel pump related. during the fuel pump change i also put in a brand new battery. also i cleaned out and re oiled my K&N air filters around that time too. (i made sure not to over oil and i cleaned the MAF sensors with electrical cleaner a week after the filters were cleaned just in case they were dirty)

any one have any ideas?

Manual or automatic trans?

manual

I have seen this happen at different times with my manual too, but never thought much about it... more or less a self check/correction...

AC kicking in and out is my guess. Mine does it. Even though the AC is on it will cycle. Back in my truck racing days we had to pull the AC fuse to keep it from coming on (even when it is off on the dash) and I would bet the same is true for these cars.

I have the same issue.. Many people told me that it could be a vac leak, but I couldn't find anything. Sub'd for answers.

My Z info : Manual Base/Sport, Mods : CBE and CAI.

Try pulling the AC clutch relay and see if it stops. Easy way to eliminate that possibility.

hmm thx guys for the answers so far!

i had this on my mustang too. It happens with some tunes. I spent days trying to track down vacuum and boost leaks and found nothing. Are you running a tune? stock tune? Maybe unplug battery for a while and let it learn idle again?

I had this happen I took my sensors out of my CAI and cleaned them and everything after that was gravy.

same thing happens on my car. rpm's dip about 300 or so for a second or 2 then the car recovers. mine has done it with the ac off as well. only noticed it after i was tuned

I had the same experience as edub in that it started after I got a tune: idle RPM is around 700 but occasionally dips below 500.

I'm going to clean my throttle bodies at some point this summer and see if that makes a difference. Some people claim they have smoother idles after cleaning them.