Throttle hang and the Idle Stepper Table
If you have a pre 2005/6 Evo and experience this problem then perhaps its the diverter valve. But if you have a 2005/6 model its the ecu causing the hang up (unless you also have a diverter valve issue). As I recall my 2005 did this when it was totally stock, and I assume all 2005/6 models do it. I've had several different diverter valves on mine and they make no difference at all with this 3500 rpm hang up issue. Isn't there someone out there who knows ecu technology and understands how car makers are incorporating these features into new cars to deal with fuel/emissions issues? Seems like there should be a way to flash around the issue. Any help greatly appreciated.
I am wondering if the throttle body seals can help solve this at all. After reading this thread
https://www.evolutionm.net/forums/sh...d.php?t=209776
I think i am going to give this a shot!
https://www.evolutionm.net/forums/sh...d.php?t=209776
I think i am going to give this a shot!
I would think that if you disconnect the IAC, then your car won't idle at all, since when the throttle plate shuts there will be zero air going into the engine...
l8r)
l8r)
Thread Starter
Evolving Member
Joined: Jul 2005
Posts: 203
Likes: 0
From: Grand Rapids, MI
I fixed the throttle hang! The solution is so simple.
First, I tried disconnecting the IACV, but the results weren't good. At first it just idled at 2000 RPM. When I tried driving the RPM would bounce around when I was in neutral coming to a stop. The throttle hang was gone however.
Next, I plugged it back in, and I completely zeroed out the entire idle stepper table to see if it does anything. I started it up, but it barely ran at about 400 RPM. I then set the low RPM region back to the original, but set the rest of the table to 30.
This eliminates RPM hang. I logged the idle stepper while driving around and it never went above 30. The drivability is still fine. In fact, the RPM's drop faster between shifts. Don't expect a lot of engine-braking, but a least the brakes aren't fighting the engine. I don't know why I didn't try this earlier. I suspected that this table was the culprit since I started this thread last September, but I never got around to trying anything till now.
First, I tried disconnecting the IACV, but the results weren't good. At first it just idled at 2000 RPM. When I tried driving the RPM would bounce around when I was in neutral coming to a stop. The throttle hang was gone however.
Next, I plugged it back in, and I completely zeroed out the entire idle stepper table to see if it does anything. I started it up, but it barely ran at about 400 RPM. I then set the low RPM region back to the original, but set the rest of the table to 30.
This eliminates RPM hang. I logged the idle stepper while driving around and it never went above 30. The drivability is still fine. In fact, the RPM's drop faster between shifts. Don't expect a lot of engine-braking, but a least the brakes aren't fighting the engine. I don't know why I didn't try this earlier. I suspected that this table was the culprit since I started this thread last September, but I never got around to trying anything till now.
Last edited by ShiftySVT; Apr 15, 2007 at 06:51 PM.
Wow man... if this fixes that issue that'll be great!!
Can you enlighten me as to why changing all these values to 30 would fix this though? I mean, Mitsu must have had a reason for the increasing values right? What does setting all these values to 30 really do?
Can you enlighten me as to why changing all these values to 30 would fix this though? I mean, Mitsu must have had a reason for the increasing values right? What does setting all these values to 30 really do?
Thread Starter
Evolving Member
Joined: Jul 2005
Posts: 203
Likes: 0
From: Grand Rapids, MI
First, the idle stepper values directly relate to amount of air that is allowed to bypass the throttle plate. When you're idling, at operating temperature, the idle stepper value is around 15-20. Thus, that's all the engine needs to idle normally at about 800 RPM. If the valve was off, it idles around 400 RPM. The stock table has values that climb to as high as 136. I couldn't see why it is necessary for this valve to ever need more than about 30 to do its job of making sure the car idles correctly. In fact I'm considering tapering the high-RPM values back down to zero. This would maximize engine braking and would only allow the valve to open when the RPM's are low enough to approach idle speed. This would be ideal for the track since it would maximize engine braking, yet the low-RPM (about 2000 RPM or less) behavior would be unaffected.
I'm guessing emissions was the driving force behind the way this is set at the factory. By lifting off of the throttle, you starve the engine of air and prevents the large amounts of fuel that has already been injected from fully burning inside the combustion chamber. The result is a big puff of fuel into the cat, where some of it is burned, but much of it makes it out the tail pipe. Mitsu prevents this by simply preventing the sudden loss of air available for combustion. They slowly decrease air and fuel, allowing the engine to continue to run close to stoich.
During shifting however, I think they reduce the idle setting to allow the RPM's to quickly fall between shifts. In this case, unburned fuel is unavoidable. They use the upper clutch switch to know when you are shifting and when you are simply lifting off of the throttle.
I'm guessing emissions was the driving force behind the way this is set at the factory. By lifting off of the throttle, you starve the engine of air and prevents the large amounts of fuel that has already been injected from fully burning inside the combustion chamber. The result is a big puff of fuel into the cat, where some of it is burned, but much of it makes it out the tail pipe. Mitsu prevents this by simply preventing the sudden loss of air available for combustion. They slowly decrease air and fuel, allowing the engine to continue to run close to stoich.
During shifting however, I think they reduce the idle setting to allow the RPM's to quickly fall between shifts. In this case, unburned fuel is unavoidable. They use the upper clutch switch to know when you are shifting and when you are simply lifting off of the throttle.
Last edited by ShiftySVT; Apr 15, 2007 at 08:41 PM.
aaaah so thats why that upper switch has a direct effect on engine braking, it thinks you are going to shift. awesome! i knew it had somethign to do with that switch. everyone had different opinions as to whether it was mechanical or ECU related., but looks like both, way to figure it out.
First, the idle stepper values directly relate to amount of air that is allowed to bypass the throttle plate. When you're idling, at operating temperature, the idle stepper value is around 15-20. Thus, that's all the engine needs to idle normally at about 800 RPM. If the valve was off, it idles around 400 RPM. The stock table has values that climb to as high as 136. I couldn't see why it is necessary for this valve to ever need more than about 30 to do its job of making sure the car idles correctly. In fact I'm considering tapering the high-RPM values back down to zero. This would maximize engine braking and would only allow the valve to open when the RPM's are low enough to approach idle speed. This would be ideal for the track since it would maximize engine braking, yet the low-RPM (about 2000 RPM or less) behavior would be unaffected.
I'm guessing emissions was the driving force behind the way this is set at the factory. By lifting off of the throttle, you starve the engine of air and prevents the large amounts of fuel that has already been injected from fully burning inside the combustion chamber. The result is a big puff of fuel into the cat, where some of it is burned, but much of it makes it out the tail pipe. Mitsu prevents this by simply preventing the sudden loss of air available for combustion. They slowly decrease air and fuel, allowing the engine to continue to run close to stoich.
During shifting however, I think they reduce the idle setting to allow the RPM's to quickly fall between shifts. In this case, unburned fuel is unavoidable. They use the upper clutch switch to know when you are shifting and when you are simply lifting off of the throttle.
I'm guessing emissions was the driving force behind the way this is set at the factory. By lifting off of the throttle, you starve the engine of air and prevents the large amounts of fuel that has already been injected from fully burning inside the combustion chamber. The result is a big puff of fuel into the cat, where some of it is burned, but much of it makes it out the tail pipe. Mitsu prevents this by simply preventing the sudden loss of air available for combustion. They slowly decrease air and fuel, allowing the engine to continue to run close to stoich.
During shifting however, I think they reduce the idle setting to allow the RPM's to quickly fall between shifts. In this case, unburned fuel is unavoidable. They use the upper clutch switch to know when you are shifting and when you are simply lifting off of the throttle.
