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Old 05-15-2000, 11:50 PM   #1
SubieRacer
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Have a Nice Day? Flat spot in acceleration!!!!!! grrrrrr!

Has anyone experienced this before? Recently my '99 RS has had a flat spot when flooring it between 4000rpm and 5000rpm! Before and after that spot the engine wants to go go go! But hit that spot, and nothing.

What's the deal here!?!

any ideas?

curtis
that damn gen x kid
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Old 05-15-2000, 11:57 PM   #2
Michael
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99 RS Turbo
Graphite Gray Pearl

Post

FYI
in some of the previous posts its normal for the stock 99RS to have a flat spot (forgot at what RPM).
Is your RS stock? if so i guess its normal
install an intake and that should take care of the flat spot.
I got a weapon R intake on my 99RS and my car pulls strong all the way to the redline.
But that is not the only mod i have
hope this helps
laters
Michael
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Old 05-16-2000, 01:45 AM   #3
Keirik
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black

Post

hey Michael....hope yer finals went well..

Anyway....I've heard of this flatspot also on the 99's..friend of mine (Keith on the board) has the flatspot..with intake, and S-AFC running also. I don't have it, but I have MY00, so it's bit different system.
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Old 05-16-2000, 04:56 AM   #4
Marius
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Exclamation

If you install an intake, try to get one that keeps the big black box just before the throttle body, it is needed as "external intake plenum".If you get one of the many "elbow style" intakes, you will have to adjust the fuel-air mixture , there are several computers out there. If not, you run lean and BANG!
Get the underdrive pulley from unorthodox racing, rev's better and flatspot goes away!
Marius
99 RS blue
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Old 05-16-2000, 05:34 AM   #5
HRE | giulio
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Post

keith's flat spot is 3k-4k rpm. my flat spot is 1k-2k rpm, but mine's not just flat, the accel jerks around a bit. (MY98+ SAFC, UDpulley, STi Mounts, Turn3 Intake)
g
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Old 05-16-2000, 07:37 AM   #6
Rajah
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Location: Cincinnati, OH
Vehicle:
2006 WRX STi
WRB / Gold

Exclamation

Install new spark plugs (NGK or Bosch +4), and lose the second air filter!! That helped my MY99 a lot!
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Old 05-16-2000, 08:58 AM   #7
Keith
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2012 J train
Brown

Post

Damn hesitation SUX! I have new plugs/intake/exhaust/pulley/Afc/and new ECU and it still happens! Only thing that works for me is to reset the ecu all the time.
ALso try different types of gas..sometimes that helps a bit
Keith
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Old 05-16-2000, 09:56 AM   #8
Gravity
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Unhappy

Sorry to hear that man, but I'll be willing to bet it's the knock sensor on the engine. See our boxer style engines are louder than most and the knock sensor thinks that the engine is pinging and retards the timing. There is a fix, but I don't remember the site. From the best of my knowledge: to fix it, one must pull out the microphone and put a piece of rubber(inner tube from a bicycle) around the microphone and reinsert it. It should take the flat spot away.

Michael

Hope this hleps.

[This message has been edited by Gravity (edited May 16, 2000).]
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Old 05-16-2000, 02:15 PM   #9
Tim Prudence
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Post

There's a kit for that fix always on sale on ebay. Search for "hesitation fix" or "subaru", you'll find it. I personally wouldn't do it though, messing with the knock sensor isn't the best idea. It comes from the factory that way for a reason.

Though if you don't plan on doing extensive mods to your car, you shouldn't have a problem.
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Old 05-16-2000, 10:56 PM   #10
kgb
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2000 RS-T -> RSTi-8
Blue Ridge Pearl

Lightbulb

Maybe because the torque maxed out?

Seriously, I don't see that in my '00 RS. I felt the other way around, at around 4K RPM, I felt a quick surge of power going to around 5K. But then again, it's only been 3500KM on mine gotta drive more often in that range of RPM.
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Old 05-17-2000, 07:55 AM   #11
Diz
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2004 Mazdaspeed MX-5

Exclamation

I noticed this on mine when it was stock. Regarding the lean run - I'm not too sure this is the massive problem everyone thought it to be. If you hear pinging, yes, it is an issue. However, I just yanked the AFC out of mine and have had no problems. I am running:

new plugs
UR pulley
2.5 exhaust
JC intake

I have not noticed a big difference since the AFC was pulled. However, I live in CO at ~5500ft and the air tends to be a bit cooler and thinner here, so that definately adds to the equation. My 0.02.

-Diz
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Old 05-17-2000, 10:25 AM   #12
Bahumut
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Thumbs down

Trust me.. It's not just the 99RS. My 95 L has it too between 2K and 3K. Sux bad. It helped to change the spark plugs, but it's still there.
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Old 05-17-2000, 10:45 AM   #13
gumball
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Thumbs up

I have the electronic hesitation fix and it seems to work fine. Bitch to install though. It basically splices in between the knock sensor and the ECU and calms down the signal a bit. If you have an ECU mod that does the same, that probably would cure it too.

Here's the text from the Subaru TSB that describes the problem, but I'm guessing this is only for those of you who can cure the hesitation by resetting the ECU- that's what I used to do all the time. Also, changing the oil seemed to trigger it too and it turns out the air displacement noise from filling an empty oil filter also triggers the knock sensor and retards the timing!

I'm guessing the 4K flat spot is something different- the problem I had was really in the low end- 2K or so.

Subaru Service Bulletin Number 11-53-98 Date: 1/5/99
Applicability: 97~98 Legacy, Impreza, and Forester Manual Transmission vehicles with 2.5L & 2.2L engines.

Subject: Hesitation On acceleration

In the event you encounter a customer complaining of a slight engine hesitation between 1500~2500rpm’s when the engine is
cold or hot, perform the following:

Eliminate all external influences, such s a incorrect or dirty air filter, loose or cracked intake duct, dirty fuel filter, low fuel
pressure, PVC system, or low engine vacuum that would indicate an external leak or an internal engine component. Check for
trouble codes and repair as necessary. Verify the fuel quality.

If all external components are confirmed to be operating within vehicle specifications, the hesitation may be caused by the
ignition control logic in the ECM. Under certain low rpm driving patterns, the ignition control system can pick up engine
vibrations through the knock sensor and may retard the ignition timing. This ignition timing is learned by the ECM and
placed in memory. Note: This area of the memory can not be viewed by using the Select Monitor. When the vehicle is driven
under these conditions, the timing may be retarded and could cause that engine to hesitate on acceleration. To confirm this
condition, road test the vehicle while viewing the Knock Sensor Signal on the Select Monitor. If you duplicate the hesitation,
and the reading on the monitor is around -10 Degrees, you will need to change the ECM to correct the concern.

Note: Some vehicles (shown on the following two charts) were produced with two different emission systems during the same
model year. To identify which system you have, look at the Vehicle Identification Number. Refer to the chart to identify which
system you have on the 98MY Forester and 97MY Impreza vehicles and choose the correct part number from the chart on the
following page.
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Old 05-17-2000, 01:28 PM   #14
AaronRS
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99 2.5 RS
Silver

Post

Wow! Do I feel better. I was freaking out when my engine hesitated at 3500rpm. I took it to the dealer and they had nothing to say. The glitch is so short and minor that I have learned to live with it. You can learn the craziest stuff in the "i"club. Thanks.

AaronRS
Silver 99 RS
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Old 05-17-2000, 05:41 PM   #15
Aaron'z 2.5RS
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'00 RS/WRX Stg5
'98 RS Stock

Post

Hi all,
I have to put my 2yen in here. I too have the "hesitation" (MY99)had it since 7500mi mark best i can remember.(almost 30k now)
Nothing works for sure as far as i've tried yet and i've tried EVERYTHING......except for Garyz fix. Home built electronics connected to me ECU don't get me warm and fuzzy.
As for the TSB from Subaru, it doesent cover the RS from what my dealer told me. The imprezas and the RS imprezas have different part # for the ECU and only reguard the regular imprezas. Someone please correct me if i'm wrong.
I've taken the REP the service manager and the lead teck for rides at different times and they still don't thing anythings really wrong.....Fu*$in SUCKS there not getting beat by damb TEMPOS........UUUUUGGGGG
Well seems i bought ANOTHER LEMON....lets see never buyin a VW or a SUBARU again.....anyone got a (gulp) Civic for sale.
AaRoN
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Old 05-18-2000, 08:14 AM   #16
SubieRacer
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Location: usa
Thumbs up

Hey everyone! Thanks a lot for all the replies! Wow! I'm not the only one! Here's my stats on when I noticed it first...

noticed at about 14,400mi

'99RS with cone filter (stock "big" box under scoop still in place)

I do need to change the oil, but I'm not over due on it

I still have stock spark plugs

Thanks again! If anyone has any other comments/suggestions, please let me know!

curtis
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Old 05-18-2000, 07:25 PM   #17
Gambit
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Post

I just joined the rank of hesitations! I replaced 2nd air filte rwith a gasket today and bam! hesitation on 4000rpm which I never had before! Before this mod, my car kpet pulling and pulling. not it pulls hard to 4000 and remained stoned for a while.... =( Well i was told to check for air leaks. If all else fails I will revert back to my old filter.
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Old 05-19-2000, 09:01 AM   #18
gumball
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Aaron, I don't know about model particulars- I'm thinking the TSB was intentionally limited in scope by SOA, but that doesn't necessarily mean the problem wouldn't be the same for other models. I guess the key is the "reading on the monitor is around -10 degrees" comment which points to the ECM over reacting to the knock sensor. The TSB also says 2.5L and 2.2L engines. If its still under warranty, I would try to see if they can cover it. OR, maybe its a whole different problem, unrelated to this?

All I know is the fix worked on my '97 Legacy 2.5GT. Re-setting the ECU also worked, so I knew it wasn't mechanical.

good luck!
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Old 05-20-2000, 12:14 AM   #19
Keith
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2012 J train
Brown

Post

the new ECU thing didnt work for me. I have some free time tomorrow so I am going to ask my dealer some questions. when I reset the ecu the runs like a champ for like 3 days!! Kinda sux...I wonder if the ITC would help that..this way I could advance the timeing at that point. what do u think?
Keith
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Old 05-20-2000, 09:38 AM   #20
stever
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Location: Costa Mesa, land of white fire hydrants
Vehicle:
99 2.5RS
Rally Blue and Black

Post

I've got the 3-4k hesitation. First only at WOT and now it's at part throttle too. I brought it back to the dealer (Metric Subaru, Huntington NY) and he mentioned the TSB and said that they'd replace the ECU and airbox with updated parts. He said that it happens to most of the cars at WOT, but not part throttle.

Same thing ... reset the ECU and it's good for a few days and then it's back. Some days it's not too bad, some days it feels like it's losing half it's power until it gets to 4k and then it clears out. The only fix I know of is shifting at redline ... then you only have to endure it in 1st gear.

BTW, my car's a MY99 with no mods. So far it's been a month since they looked at it and no new ECU yet ...

Steve
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Old 05-21-2000, 04:51 PM   #21
Narso
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1999 2.5 RS
Aspen White

Question

Folks,

My MY '99 doesn't have the hesitation problem many of you are having. I noticed a few days ago that I don't have the second air filter installed on my car. Maybe the hesitation problem is related to the second air filter.

Just a thought ,
Dan Z.
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Old 05-21-2000, 05:04 PM   #22
ownly
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Mellow Yellow

Post

AFC+ITC+5Zigen cat-back= ownly very happy

that worked for me

O/...
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Old 05-21-2000, 10:21 PM   #23
Keith
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Vehicle:
2012 J train
Brown

Post

Hey Steve,
Cool another metric customer I am there all the time, I love that place. what part of the Island are u from?? Hey if u are interested, me and a couple guys from Metric subaru (craig, white 99 rs, and dave, 98 legacy wagon) are going down to an auto-x at nassau col on the 25 and 26 of june. ur welcome to come.
Keith
EDIT: Steve, I know u! U have the blue rs. I met u at the last LI meet right? We were talking about the 22b fenders. I'm that short guy with the white impreza...I was hanging out with craig most of the time
Oh btw, if this is not u...I'm just kidding


[This message has been edited by Keith (edited May 21, 2000).]
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Old 05-22-2000, 07:03 PM   #24
stever
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99 2.5RS
Rally Blue and Black

Post

Hey Keith,
Yeah, it's me ... blue MY99, I remember you. I'm up for the auto-x if I'm in town, might be on the way to Cali to have 22B fenders put on. I'm in Huntington.

Sorry this is off topic ...

mailto:sramm@optonline.net
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Old 05-22-2000, 07:13 PM   #25
NotAnRS
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Scratch-n-Dent Blue

Unhappy

My experience is with the under 3k hesitation. It is caused by the knock sensor system. I wonder, though, if it really is over-sensitive as we tried running a tank of super through it and didn't have any coughing. Next tried a tank of 89 octane and right back where we were. So I'm hesitant to alter the knock sensor system for fear it may actually be working correctly, thus preventing detonation. This is what we get for having high compression engines I suppose.
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