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Low RPM stutter in gear and air fuel ratio question

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Cam2Tezza
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Joined: Fri May 15, 2015 2:52 pm

Low RPM stutter in gear and air fuel ratio question

Postby Cam2Tezza » Thu Aug 20, 2015 12:39 pm

Hi,
'00 RS200 manual, stock ecu, drop in K&N filter, Tanabe exhaust
Had my TB issues recently but since they're fixed I'm moving on to other things I noted.
I have an issue when I'm in gear near idle RPM, when I give it a little throttle, it will accelerate to maybe 1200 Rpm, then for a split second feel like I hit the brakes and then continue normally. It's not a speed drop but more like a pause for a fraction of a second. I say hit the brakes because it's the same sensation where you lean forward, but physically I don't think I actually do lean, as it happens too quickly. Imagine a linear line graph of speed there will be a small chip or spike in that area. Most noticeable in 1st to 3rd but should be the same in higher gears, just more subtle and almost never accelerate near idle in 6th. I can replicate the issue everytime.

Can a bad MAF cause this? I've cleaned it with CRC MAF cleaner and the throttle body, reset ecu but it hasn't changed. Also not sure if my idle is acting funny, AC off it will idle around 700-750, AC on it will be at 750 without brakes, then over a few seconds it will very slowly creep to 800-900. If I come to a stop and keep my foot on the brake, with AC on it will drop to 700, then again slowly creep to 8-900, sometimes it may just fluctuate very slightly. I thought it was due to ecu reset but after 2 tanks of gas over 1000km it still does it.

And on to AFR, I passed emissions and looked at the slip they gave me, it says AFR is 20.5 at idle, 15.1 at 2000rpm. I'm wondering if there's any correlation to my low rpm stutter issue. The closest description I could find of my issue was from an S2K threadhttp://www.s2ki.com/s2000/topic/871532-slight-hesitation-at-low-rpm/

Last thing just checking with everyone else, first start of the day takes 5-7 turns, but warm restart jumps to life on 3rd turn but sometimes takes up to 5-7 turns as well?

Thanks again for any help I can get :D

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Tosh21
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Joined: Mon Jan 20, 2014 10:12 pm
Location: Oxfordshire

Re: Low RPM stutter in gear and air fuel ratio question

Postby Tosh21 » Thu Aug 20, 2015 10:56 pm

Ive got a wideband on mine and it will read about 13 on cold start then lean off as it warms up. Idle is off the scale lean, as is off throttle and during normal driving it is about 14.7-15. and full throttle its goes to 11 ish. It used to be at 15.6 but its richened up a bit (think I was having pump issues which seem to sorted now) so your afrs seem reasonable. That's if my car is right ofcourse!

Cam2Tezza
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Posts: 19
Joined: Fri May 15, 2015 2:52 pm

Re: Low RPM stutter in gear and air fuel ratio question

Postby Cam2Tezza » Fri Aug 21, 2015 5:33 am

Thanks again Tosh, do you or anyone else experience what I'm experiencing at low rpm though? Just want to know if it's a quirk of the altezza or something else... Which will prompt me to look further into it since it's quite annoying in traffic.

oaasport
Trc On!
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Joined: Sun Apr 26, 2015 2:25 pm

Re: Low RPM stutter in gear and air fuel ratio question

Postby oaasport » Sat Aug 22, 2015 3:29 am

Does the car sound like a dry cough when it is starting? If it does check all the fuel lines for leaks. If it sounds like a dry cough its not getting addequate fuel. Air getting into the lines can cause A sutter, might not be a good suggestion but might be worthlooking into

Cam2Tezza
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Posts: 19
Joined: Fri May 15, 2015 2:52 pm

Re: Low RPM stutter in gear and air fuel ratio question

Postby Cam2Tezza » Sat Aug 22, 2015 9:56 am

Hi, not sure what you mean by dry cough, I recently replaced my FPR and fuel filter which solved a hard restart issue, although I left the pump alone. My cranking question is just that, a question, not really an issue, just that I noted that on restarts within anywhere up to 3 hours sometimes(~80%) of the time it starts really quickly, almost too quickly (1-2-VROOM) but sometimes it will start like the first start in the morning where it starts on up to count 7, I've read and presume it's due to the stock ecu not priming the pump when you turn to ON unlike most other cars, but on restarts fuel pressure should not have dropped much (stop to refill petrol) so I was just wondering if my occasional restart that takes slightly longer like a first start is normal.

I unplugged the MAF and had a go around the block, it would stall at lights occasionally and jerk real bad at 3000rpm(limp mode?), and just when I thought the stutter was less noticeable it came right back, so it was probably just me really wanting it to be the MAF lol... I swapped my TPS with the old one and it did the same thing so probably not it. Please correct me if I'm wrong though.

I noticed when i first apply throttle, the revs will drop very slightly a hair before climbing, is this normal?


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