I know that there have been a lot of threads on this already, but I have read as many as I can find and have yet to come to a conclusion.
I just got my IX MR about a month ago and ever since I got it, it has been doing the whole bucking issue at partial throttle. This is where i'll be driving and if I let off the throttle or get to partial throttle the whole car jerks until the throttle is completely let out. Then when I put the power back on it jerks a little more but doesn't seem to be as bad. It happens mostly when boost is involved so if I drive it like a grandmum it's fine, but when I give it a little spirited driving (like when I drive an awesome canyon up to my ski hill) it gets real nasty. I have never had this happen on any other car I have ever owned.

The only mods to the car are a catback exhaust and a k&n intake (filter right on maf). Apart from that the thing is bone stock and it seems to not have been fooled with apart from those two things. Since I have had it I got the 60K tune up at the Mitsu stealership and they all is shipshape. But I know...I know...don't trust them that much. However I am new to the CT9A 4G63 system and I am trying to learn as much as I can.
So my questions are:
1. Can the oem metal diverter valve go bad over time? The car has about 79K on it.
2. I would assume they are not adjustable correct?
3. How can you tell if the spring has been "crushed"?
4. Any idea's what this issue could be?
I am not hearing any compressor surge. Every once in a while under supper light boost and throttle it'll flutter a tad. But under heavy boost and wot it dumps perfectly and no surge (that I can hear anyway).

On a side note, I have noticed that if I am in gear and wind it up into boost but let off the throttle and push in the clutch the rev's jump up a little and it makes me look silly, like I miss shifted of something. It seem's like these two issues could be related.
As I said I just got the car, and after a month of driving it I love it but it certainly seems to be quite touchy and rough (not like with the idle or anything, just kinda hard to drive, a little, haha).

Anyway, I appreciate the help guys, I would really like to get this sorted.

Cheers

Chris

 

1:Anything can go bad. So yes.

:No, unless you consider crushing them adjusting them.

:The top of the diverted will be pushed in.

:Possibly not having any kind of tune to go with the KnN and exhaust.

I would start troubling shooting this by removing the filter and cleaning the MAS out with MAS cleaner. People tend to over oil these things and oil ends up all over the sensor making things act crazy. If that doesn't work I would put the stock intake back on and see what it does with that. Also go over ALL of your vacuum/BOOST lines and make sure there are no holes and they're properly connected. Do this with your inner cooling pipes as well.

 

^this.

Do a boost leak test. This will also tell you if your diverter valve is leaking.

 

^^ Do a boost leak test and go from there!

 

Gottcha! I'm out in the garage cleaning the MAF right now, i'll let you guys know what the results are. Thanks for the help.

On another note, I took a quick drive today and while I was out I tested to see if the car would do this while it was at low rpm and no boost at all and it still actually bucks a little. So I'm curious if this might be due to a drivetrain issue. I've had a root around underneath and all seems to be spot on. No driveshaft play or any issues with the U joints...

 

Hey, you still have that jerking going on with your car? Did you buy your car used? You might have an aftermarket clutch and that could change your car's drivability.

 

I had that issue before I installed the Spoolin-up COP.

 

I encountered this when my car was brand new. I came from a turbo awd DSM that had the same engine as my Evo and I was still having problems. Well, I didn't know how to drive an Evo. Driver mod was the fix.

 

sounds like it could compressor surge or part throttle boost

 

It's something I'm tackling right now. From what I gather, it's fairly common and involves your diverter valve not opening completely and forcing the air back through the turbo (previously mentioned compressor surge)

Highly annoying when I'm at freeway speeds in the mountain passes. Right now I've learned to live with it and adjust my driving to minimize it. When I get into boost, I keep my foot into it and slowly ease off until the gauge reads vacuum but not cause the shuttering. Or just let off completely. Takes practice.

I recently had to buy new tires and pay for clutch and labor, so I'm not ready to throw more money at the car to fix this problem =(

 

i purchased a synapse bov which is known to help with this and it reduces the problem a lil but not completely. the only way to rid of this would prob be an anti surge turbo housin

 

compressor surge is when you turbo inhales so much air that it starts running into that air and jars the turbine. when people usually refer to surge they are mistaken. its under really high boost relative to the turbo size and normally under WOT only. thats why true surge will destroy your turbo.

Evo's are very well known for the bucking at partial throttle. the only real cure i've heard of is switching to Speed density. on my first tune on SD it had no bucking what so ever but was terrible stock and the only thing i did was change to speed density.

things that i have heard help are a better ignition system, ie COP,
a slightly bigger gap, .026, which i dont recommend without COP.
or a very detailed road tune by a very skilled tuner. email flash isn't precise enough from what i have seen to get it exactly right unless they get lucky.

 

I had some nasty bucking when I got my car back.
1st, I made sure my synapse had a dedicated vacuum source, this reduced the bucking a lot.
2nd, I put my synapse with stock spring into Aby@Mil.Spec's recommended config.
Car was very civilized. could still induce an abrupt jerk IF I TRIED to.

3rd, I put Aby's spring in the DV, replaced the two worm clamps holding it in with T-bolt clamps and got rid of the quick release actuator hose and went to traditional hose although felt it was a little loose. Running it in Aby's recommended setting, also.
Car was more or less the same. No big diff.

4th, I replaced the last two worm clamps in my UICP, the route to DV and the TB with t-bolt clamps. and replaced the DV actuator hose with a new better fitting one. It's probably only psychological but the car seems even more civilized and I feel more confident in my setup.

I don't know if any of that is helpful information but I hope so.