DTN

I would say my car is in tip top performance condition, except for the fact that it has a rough idle below 900rpm and the steering wheel shakes at idle. I have no clue what causes it, but it does it. Everything I try seems to fix it for a day and then it comes right back. I've also got no CEL

These are my fuel economy statistics as reported by Jay-M's ELM 327 reader





This is my car's performance profile as far as things which I feel might possibly effect shaking and gas milage
-87 octane
-NGK R spark plugs - $20 from hyundai pregapped to .41
-new spark plug wires from advanced, chepest and came in a red/blue/black box and were the lowest resistance
-new oil change
-XTD stage 3 clutch
-lightweight flywheel, balanced
-Old style Chrome Intakes CAI - ebay/not available any more
-BOMZ chrome Y pipe - ebay
-JDM Motors 4-2-1 header - ebay
2.25" exhaust including magnaflow catalytic converter, cherry bomb glasspack, cherry bomb turbo muffler- ebay/rock auto

aero gas milage only-
- Turbulence side skirts
- Scoote hood - ebay - weighs about 20 lbs at max
weight gas milage-
- Drag dr17 rims lightweight rims
-100 lbs extra weight including amplifier, speaker, tools, cleaning supplies, full tank of nitrous oxide, that kinda stuff
-driver 200 lbs

Other troubleshooting with no results:
-new all 4 engine mounts
-canadian 2.0 ECU
-IAC working properly tested and replaced, then tested again
-IAT replaced
-MAF replaced twice off-the-shelf at advanced
-replaced TPS from Dae Sung to Kiefco and again to off-the-shelf at advanced
-evap solenoid working properly, electrically tested and audible clicking
-both o2 sensors replaced
cyl pressures 1 205, 2, 204, 3, 205, 4, 205 January 09



These are some previous readings, I don't remember what I was using before the things which I mentioned were new, however the aerodynamics of my car were effected by a ATH roof spoiler and a GT Tech lip. The car was run on 89 octane.

85mph


70mph



Here's some of the things I've come up with as far as things that effect millage. It does not relate to this thread, but It's great information. These tests were conducted at 70mph
Sunroof up -1mpg
sunroof back -2mpg
windows down -1mpg
a/c -5mpg
uphill (average 10-15% grade overpass)-8mpg
downhill (average 10-15%grade overpass)+7mpg
drafting semi truck ~ +8mpg
drafting car/truck ~ +5mpg
uphill lowest mpg 23mpg
downhill highest mpg 55 mpg

I would like to get input on my severe shaking at idle, when stopped, and if anyone else has fuel economy readings, please post them. This could be two threads put together, but really I feel it may be pertinant information to solving my rough idle problem.

REDZMAN

With the performance stuff you've done to your car, 900, and below 900, is probably too low for your idle. Adjust it a bit higher.

I hate to tell you, but I highly doubt you are getting anywhere near 39 or 36 MPG. Figure your MPG the foolproof way with your trip meter and the gallons you've put in the car, it's easy to do, and will get you the actual fuel economy.

Your idle is probably rough as it is because it's too low, and you have that engine damper too.

HyundaiKitCoupe

it shouldn't go below 1000 though. i mean maybe 950, never below 900. everyone says this and it's annoying but adjust your throttle and see what that does.

it could be that it's cold.

that's some cool information, however i also doubt it's 36-39 mpg. it's more like 23 or 22. but then again you can never really know for sure.

REDZMAN

I know it's posted somewhere, I think that OEM idle is supposed to be 900 to 950.

Below 900, yeah, you're gonna shake like a crackhead.

2uniq

I have the same issues as DTN where my car shakes like crazy.
It started for me last year in Sept and i also cant figure out the problem as it ONLY shakes at idle
My car is at 1000rpms at idle and even before i installed the engine damper i had this problem...
It drives me NUTS...... mad.gif


Any help would be great

stealth

same problem here, only mine does it sometimes, but its been doing it for a long time now

mine also fluctuates on idle, i know TPS does that but what pisses me off is i just bought a TPS (kefico) and it needs replaced already

DTN

ok,first, you cannot adjust the idle in the car. The IAC compensates. If you go beyond what the IAC compensates for, then it kicks out a high idle code.

<div class='quotetop'>QUOTE ( HMAService.com)</div><div class='quotemain'>Basic idle rpm 800 ± 100 rpm Idle speed when air conditioning is on 850 ± 100 rpm</div>

When my A/C is on, the engine idles even rougher and at a higher RPM. But normally, at about 900RPM, it kicks out and stops idling rough. My car idles at about 850rpm and just below 1000 is where the idle evens up. It's like it floats down and when it settles at idle, the car just starts shaking badly.

Blue Bomber

Hmm... my idle is at like 700 rpm alot of the time.Sometimes drops lower. I take it thats a bad thing then?

REDZMAN

<div class='quotetop'>QUOTE (DTN @ Feb 15 2009, 07:14 PM) <{POST_SNAPBACK}></div><div class='quotemain'>ok,first, you cannot adjust the idle in the car. The IAC compensates. If you go beyond what the IAC compensates for, then it kicks out a high idle code.



When my A/C is on, the engine idles even rougher and at a higher RPM. But normally, at about 900RPM, it kicks out and stops idling rough. My car idles at about 850rpm and just below 1000 is where the idle evens up. It's like it floats down and when it settles at idle, the car just starts shaking badly.</div>


Uhm, yes you can. I've adjusted mine a few dozen times. There's an idle adjustment screw on the OEM TB. There are adjustable nuts on the throttle and cruise cable that you can also adjust to adjust your idle.

There are also instructions on HMAService about how to adjust it.

Your AC saps engine power, lowering your idle, so it shakes more.

The IAC doesn't compensate for anything, it just provides a way for air to get by when the TB is completely shut. From what I understand, the IAC is OPEN or CLOSED, nothing else.

Of course, you can just let your car shake like an epileptic during a seizure and say I'm wrong. Enjoy.

Lorf

Mine's been idling rough for a while now, seems to be around 800 rpm. How can I fix this?