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Anyone else having a rough idle?

2464 Views 11 Replies 9 Participants Last post by  bi11y
I have about 1100 miles on my STi now. It has been very hot and humid here lately.. 90-100 degrees farenheit. When I have the car parked and just sitting there letting the engine idle for a while.. the engine will rumble randomly.. Could this be detonation? I never notice a change in rpm when at idle.. it always stays at 500 rpm even if it rumbles (shakes the car slightly) or if I have the air conditioning on or off.

I am using 93 octane pump gas.. I notice this happening whether or not I've used a bottle of octane booster or not.

I have not noticed detonation happening under hard acceleration yet.. although I've yet to go past 6000 rpm.. and even then only during a slow pull at high speed in 5th or 6th gear.
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Im betting its the fan. Can't think of anything else...
Re: Black on Silver - Nebraska - Took Delivery

I noticed the rough idle from day #1 (now has 440 miles). I also noticed how @#$! fast this engine spools up to speed, then it all made sense. Combine the hollow valves, hollow cam, lightweight flywheel, etc. and you have a very low inertia engine. Sometimes the vibrations cancel out and it's smooth, a few revs later they superimpose and it's rough.
Sounds like something my 4Runner does, at least this is our assumption. The front rotors are warped and sometimes you dont notice it and sometimes its really bad. I think they eventually cancell themselves out after a lot of steering. But thats just a guess from a uneducated person! :p
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