i have noticed that my car has been sort of weird at startup for the past month.

when i first start the car, it will rev up to like 3k for a few seconds (this is normal i know), and then the car will just idle.

here is my first concern: when the car is at idle, every few seconds it sounds like the car makes a little sputter noise. like a fart almost. lol im not really sure how to describe it.

my second concern: after driving my car (daily driving, nothing hard), when i am driving slowly like through a parking lot or whatver, and then park, the engine sometimes revs up and down between 500 and 700 rpms for a few seconds even though the car is in neutral. is this normal?

i might have to record a little audio/video to show you what i mean, but what do you think these might be?

as far as engine mods i have:
-HKS carbon/titanium exhaust,
-K&N intake w/ polished pipes and K&N breather on airpump

my car has about 40k miles on it now, and i do pre-mix with 4oz of royal purple TCWIII 2-stroke on every fuel fill up. i just changed my fuel filter about 6 or 7 months ago. i dont have any boost problems (10-8-10 still), and i pull 15psi vac. at idle. everything seems fine, and the car drives great still, but the 500-700rpm reving is just stuck in the back of my mind.

any ideas?

 

The 'farting' may be due to your exhaust. When did you get it?

Have you done any electrical work? New radio? Changed the battery? I had a lose positive battery cable.

 

My car sputters a little at startup. I was curious as well if this was normal. It goes away though as soon as its warmed up.

 

nope, all the electrical stuff is stock.

i do have a turbo timer, but i doubt that would mess anything up. i installed the timer with a harness so i didnt cut any wires.

the HKS exhaust was brand new when i bought it a few months ago from www.intensepower.com (pretty sure thats the address)

i guess if it starts to affect anything, i can take my car over to Lowe's Rotary Automotive Performance just down the road from me.... they know their stuff really well so they could take a peak maybe...

 

It's probably just fine, as long as we're talking about a warm engine and there's no smoke or anything.

 

How old are the spark plugs?

 

I meant "COLD engine" A warm engine should be pretty damn steady when the A/C isn't on.

 

It's not abnormal to have some 'farting' out of an aftermarket exhaust. My RB Duals do that, while the stock hardly ever did.

I doubt its your turbo timer but try turning it off to see if it makes a difference while the rpms fluctuate. Don't think it'll be the TT but you never know till you try.

V

 

On my first rx7, it was bone stock. But when I put a reman engine I had a problem with it idling up and down after drive to a stop. I thought it would go away after the break in period but it didnt . Come to find out, one of the vacuum lines under the stock vacuum hell manifold was cut and had a vacuum leak in it, swaped it out and that cured everything.
Everything seemed normal on the boost gauge too when the bad idling occured.
Another time that I had bad idleing was when my alternator was going bad. At first I tried changing the spark plugs but it didn't help,so then I sat and sat and finally tested the alternator and got a new one.
Good luck I hope my experience helps.

 

yeah i just put new plugs in when i hit 30k miles a few months ago. now i just hit 40k miles so they should still be fine.

im pretty sure the prob. is the alternator or battery now.

mainly because when the car is just sitting there, if i tap the brakes the gauges dim.... LOL

i posted a different thread asking about this specific prob though.

i did manage to fix the 600-700 idle reving but just opening the idle screw a little bit.

 

Sounds like alternator might be faulty. If you brake and the lights dimm it could be the alternator is not charging the battery properly, or the belt may just be loose and you are loosing a charge.

 

I would pull my plugs just to check because that is what it sounds like to me as well. I have had the same issue in the past and the plugs have been the culprit. I try to change my plugs at least every 7500 miles or so. $20 is nothing if you think about the amount of trouble a fouled plug can cause and how crappy it makes the car feel.