any updates?

 

Today i have been looking over the whole car. checked all hoses etc.. guaranteed a ecu problem... If not please let me know when you find out what the problem was and ill send you a your my hero sticker

 

not a ecu issue. happening to people that are completely stock. also, i got a reflash and it didn't solve my issue.

 

yes i just said that a bit earlier that my car was stock

I know some ppl with similar problems but they have changed their ecu to motec but its not mapped yet either so well i dont know..

 

My greddy type s was causing the rpm spike. It worked fine for a long time then it started happening for some reason. I took out the BOV and replaced it with the stock one and problem solved. When looking at the Greddy, I noticed the bolt for the nozzle where the vacuum hose went into the BOV was loose, also there was rust all over the spring and it seemed to be a little sticky when pushing on the spring. After cleaning it up and tightening all hoses/clamps, re-adjusting spring tension it worked fine with the Greddy, no rpm spike anymore. BTW i was getting a bad spike usually around +500rpms when i hit it right. Anyway check all hoses and clamps and bolts going to your diverter valves. It seemed to be a vacuum issue for me.

Hope this helps

BTW only other mod i have is DynoFlash

 

i just discovered this thread today, i can't believe this happens on evo8s. For me it's a reason big enough not to buy an evo. I own a galant vr4 and this happens on my car as well. I thought it's because the car is old and stuff but now reading this thread i know it's not my car. My car had the same problem ever since it was standard, since then i put a performance chip to fix the problem, changed the factory clutch with exedy sports organic clutch (thinking the stock clucth wasn't disengaging quick enough), and finally i removed the factory cruise control unit with a cable that goes straight to the throttle body (i thought maybe the throttle wasn't responsive enough and might have sthg to do with butterfly not responding as quick). After all this the problem is still there and annoys the hell out of me. All i can say is i'm not as passionate about buying an evo anymore. By the way i can think of one more fix to this problem, and that is ligtened flywheel since the revs drop quicker with it.

 

Ok, here is my theory.

1. The clutch sensor maybe out of align. I'm going to check upon this tomorrow. This is happening to my friends stock evo.

2. It's the worn out clutch. The slave cylinder adjust to the wear on the clutch and pushes the clutch up as it gets worn out more and more. So this could change the clutch engagement point, where it would engage the same speed yet disengages a lot slower.

This is what I'm thinking but some people are having this issue with very low miles on stock clutch. But most people had their problem solved by replacing the clutch, like snoop and few other people.

3. It's the worn out clutch and mostly the throw out bearing being too worn out. The technicals are earlier on on this thread by snoop.

4. It's your air filter being really really dirty. This could cause the air to just get stuck in the intake box and gets pushed back into the intake piping.

The air travels back and forth on the intake pipe (in our case, upper intake piping connected to the intake throttle) as the intake throttle body opens and closes. But when the air cannot vent out to the filter, it gets trapped and it stumbles the air still in the upper intake piping thus causing the RPM to rise slightly after the throttle is off.


Mostly, I think it's got to do with your clutch, because from what I see, people with stock clutch is having this problem.

That's my update on this.

I hope someone figures it out definitely, so people could get their car fixed.

I'm thinking, this could create a lean condition in the engine, because if the air trapped in the intake piping could be causing this while the throttle is off, it could just be a small fuel to a lot more air in the engine. I really hope I'm wrong about this.

My friends going to change the clutch and hopefully this could fix it.

She did briefly fixed the problem after taking the dirty filter out and running the car without the filter.

keep it updated.

 

Even if it did create a lean condition like you suggested, it wouldn't be of a concern, because it is done with no throttle applied, and under no engine load. The momentary "lean" would not be severe enough to do any harm at all.

Forgive me, but I am really still skeptical about how this is happening to DIFFERENT types of cars with DIFFERENT engine management systems, DIFFERENT clutches, DIFFERENT climates, and DIFFERENT modifications. In other words, what is common to all of these cars? I know you don't want to hear my theory, but I still think it needs a bit of consideration.

 

The only thing common on these cars is the 4g63 (incl. my vr4) which makes me thing the problem is engine related. Plus the rev increase or pause situation occurs in stock standard cars as well as modified ones.

What's interesting is my car is 91 model (first vr4 introduced in 87-88) and evo8s are 03-05 model, there is like approx. 15yrs gap in between. Still it's the same problem. I would like to hear from other series evo owners to see if there is an engineering stuff up.

 

aiight guys, listen up!
My car finally is fixed for 100% sure.
I cannot pinpoint what happened but here is the story.

i have mods on my car. 3"tbe, mbc, cams, fuel pump.
my car started to do this rpm rising thing. it happened all of a sudden. I didn't add a new mod and then start getting this problem. recently i got injen intake/upper ic piping along with a mail in flash from dynoflash at the same time. guess what, the problem is completely gone.

so, there is my story, go figure. I don't exactly know what it was but it may have been intake issue since i was running stock airbox before. or it may have been an ecu problem.

I'm so glad i don't have this problem, hope you guys fix your problems. pm me if u got questions.

 

I discovered most of these issues are due to a combination of several things, but almost all cars experiencing it will have one or more of these things in common..

Generally, its the MAF sensor reading additional airlfow after the throttle is snapped shut, sometimes its the BOV, sometimes its the wastegate not opening quick enough to drop the boost...

This never happened until I started playing with a blowthrough MAF sensor, but what I discovered was I was able to measure an increase in airflow (MAF reading) between shifts even though the throttle position would drop.. Since there's no load, the engine RPM would suddenly shoot up..

1) Make sure your BOV is operating correctly
2) Make sure your wastegate actuator has the correct preload on it..
3) try to use an intake thats as long as possible and as far away from the BOV Recirulation fitting and compressor.. This will reduce the possibility of additional air reversing through it, or being drawn suddenly through it by the turbo..

Also, I noticed it was happening to me when the air got cooler.. Denser air and more air volume, the BOV didn't vent enough air, quick enough.. There's a good possibility that many of these aftermarket BOV's don't vent a large enough amount of air fast enough when they open..

Hope this info helps a little.

 

Actually the only thing besides the engine they both have in common is a recirculating Diverter valve, and KArmann sensor.. I have been able to measure a MAF frequency increase.. It may be an engineering flaw in the intake design, or an adjustment in the wastegate actuator's preload on the flapper..

 

ok, just got an oil change and it started to do this on my car. When I take the Filter off of my stock box and run it, the rev raise doesn't happen, but only when I have the filter on, it would do that.

I still get the momentary pause between the shift, which is annoying without the filter.

It was running perfect before this. I do believe the weather is something to be concerned with but I don't exactly know how to put the filter relationship with the cold weather.

My friend just bought the K & A drop in filter and it's still doing it. but without the filter, it wont do it, the rev raise. But the momentary pause is still there.

 

My RPM Raise issue started happeing before it got cold.... I think mine might be BOV related, ever since I went the the Forge BOV from the HKS I had before the RPM raise is not as bad or as frequent. I am going to try another spring in the Forge to see if it helps.

 

Anything that alters the airflow through your MAF can cause this.. basically what is happening is the airflow value in the MAF is still climbing even after the throttle is snapped closed.. there's several reasons this can happen..

In my case I discovered this when I put a blowthrough sensor on my car, and the BOV I was running was still building a little pressure even after it was blown off..

Anyway, what was happening is when the throttle blades snapped closed, it would momentarily go rich, then as the airflow restricted, it would go lean, and the engine speed would rise..

your right, this wouldn't happen all the time, what I did notice was when my car was cold and the induction system components haven't absorbed heat into them, they seemed to cause the metal bodied BOV on my car to "Stick slightly" or open slower than normal.. Once my car was up to operating temp, it didn't seem to hapen anymore (or at least I had trouble reproducing it)

The best thing I can gather from it is altering your airflow patterns and restrictions in your car, In the case of the BOV, its likely not venting completely and there's still some positive pressure in the upper intercooler pipe "forcing" its way through the idle circuit between shifts causing it to raise.. since there's no load in the engine between shifts, the engine speed rises as the air sneaks past.

In the case of the intakes and air filters, you've lowered the restriction THROUGH the maf, so air being drawn into it easier before the turbine speed can drop so the MAF reading remains high.. In your case, check your BOV, and your Wastegate preload from your wastegate actuator.

Those two things should address a majority of these issues..