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420A HELP REALLY HIGH IDLE! 420A

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Daniel b

Proven Member
71
6
Sep 15, 2021
Middletown, Rhode_Island
So I ended up having a idle at 1200rpm and a evap leak which I assumed the idle was high because evap leak found a leak At throttle body replaced throttle body gasket then ended up having idle surge when it was warming up to around 2000rpm then changed iac and went through the learning ecu for it and when we were test driving it I noticed that the rpm would spike up to around 3000rpm when coming to a stop at stop sign then go down but on my way home out of no where rpm started jumping to 5000rpm randomly had to turn off car a couple times and let it roll in neutral to get home but when I start it up after letting it sit it goes to 5000rpms instantly. If anyone has a idea what could be causing this that would help a lot thanks.
 
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A typical cause for high idle are vacuum leaks but check the throttle cable adjustment. You want a little slack when it's closed and idling.
 
yeah

I changed it back to old one and idles around 1700rpm and acts weird when coming to a stop but not as bad anymore I found this fix on a forum just trying to find where it is on 420a https://www.dsmtalk.com/threads/i-solved-my-perplexing-idle-problem.83947/ any ideas?
Ignore everything you read in that thread on DSMtalk. That is a 4g63 with a closed throttle sensor and biss screw. You have neither

Now that the idle is down lower have you tired spraying carb cleaner around the throttle body and intake area to check for vacuum leaks?
 
Ignore everything you read in that thread on DSMtalk. That is a 4g63 with a closed throttle sensor and biss screw. You have neither

Now that the idle is down lower have you tired spraying carb cleaner around the throttle body and intake area to check for vacuum leaks?
Yeah couldn’t find any after spraying apart for the first leak at throttle body which I fixed
 
So somehow air is getting into the intake that shouldn't. Just going to rattle a few things off the top of my head that I can think of that would cause this that carb spray wouldn't effect. Others may chime in with more

-Check for hissing under the dash while the car is running. Brake booster could have a bad leak
-Since the other IAC you had was obviously bad you still haven't ruled out the IAC
-Make sure the throttle plate is closing all the way I know you said the cable had slack but I would take the intake tube off and check that plate is physically closing all the way
-Make sure the PCV valve isn't sticking open
 
So somehow air is getting into the intake that shouldn't. Just going to rattle a few things off the top of my head that I can think of that would cause this that carb spray wouldn't effect. Others may chime in with more

-Check for hissing under the dash while the car is running. Brake booster could have a bad leak
-Since the other IAC you had was obviously bad you still haven't ruled out the IAC
-Make sure the throttle plate is closing all the way I know you said the cable had slack but I would take the intake tube off and check that plate is physically closing all the way
-Make sure the PCV valve isn't sticking open
Yeah I checked the throttle plate when I cleaned it out I’m going to check to hear the noise you said under the dash.
 
So somehow air is getting into the intake that shouldn't. Just going to rattle a few things off the top of my head that I can think of that would cause this that carb spray wouldn't effect. Others may chime in with more

-Check for hissing under the dash while the car is running. Brake booster could have a bad leak
-Since the other IAC you had was obviously bad you still haven't ruled out the IAC
-Make sure the throttle plate is closing all the way I know you said the cable had slack but I would take the intake tube off and check that plate is physically closing all the way
-Make sure the PCV valve isn't sticking open

I didnt hear anything under the dash.
Can a map sensor cause the idle issue?
 
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map sensor will not cause a high idle unless it is not sealing.


disconnect the evap line on the throttle body, put a vacuum cap on the nipple
check idle >>>> not fixed >>> reconnect evap line
disconnect a vacuum line on the intake manifold>> cap nipple>>> check idle
>>> repeat procedure on next vacuum line>> until you find the vacuum leak.
 
map sensor will not cause a high idle unless it is not sealing.


disconnect the evap line on the throttle body, put a vacuum cap on the nipple
check idle >>>> not fixed >>> reconnect evap line
disconnect a vacuum line on the intake manifold>> cap nipple>>> check idle
>>> repeat procedure on next vacuum line>> until you find the vacuum leak.
Ill try that thanks
 
I bought a box of universal vacuum nipples at the autoparts store when I was deleting all my vacuum junk. But they are very useful for plugging various ports where you suspect vacuum leaks. As @dustyboner stated, try capping off the evap port or other ports that may have a leak down the lines and see how it affects your idle. The vacuum port for the EVAP system is on the top of the stock throttle body. You can see in my picture I had a red cap installed.

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Oh alright thanks I’m going to try it today

Here is a video
It also has a misfire on cylinder 4.

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your car sound like its got an intake but its got the stock filter box. Unless its just cause its a video, but i hear the sucking sound you get at the filter when you put on a cone filter.
anyways
maybe your egr valve is sticking open from carbon buildup. you can unbolt it from the head and clean the valve seat.
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maybe your egr valve is sticking open from carbon buildup. you can unbolt it from the head and clean the valve seat.

Yeah I swapped the egr valve too but no change it’s like the hotter the engine gets the idle rises like when I come back for a quick drive and park it it idles around 2100rpm

Yeah so I cleaned egr no difference and it’s weird because when slowing down to a stop the rpm surges,
 
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Sounds more and more like an IAC issue. Especially since you said it changed a bit when you swapped them over. Try removing your IAC and turning the tip counterclockwise a couple turns. It should idle down. I'm on my 4th or 5th IAC because of idle issues. I ended up removing the tip and putting Loctite on the threads to hold it in place because it kept screwing itself farther in and causing the car to idle up. I have my tip unscrewed as far as it will go so the car idles around 700 rpm and the cams sound aggressively choppy despite being stage 1's.
 
Sounds more and more like an IAC issue. Especially since you said it changed a bit when you swapped them over. Try removing your IAC and turning the tip counterclockwise a couple turns. It should idle down. I'm on my 4th or 5th IAC because of idle issues. I ended up removing the tip and putting Loctite on the threads to hold it in place because it kept screwing itself farther in and causing the car to idle up. I have my tip unscrewed as far as it will go so the car idles around 700 rpm and the cams sound aggressively choppy despite being stage 1's.
Oh alright I’ll try that
 
Sounds more and more like an IAC issue. Especially since you said it changed a bit when you swapped them over. Try removing your IAC and turning the tip counterclockwise a couple turns. It should idle down. I'm on my 4th or 5th IAC because of idle issues. I ended up removing the tip and putting Loctite on the threads to hold it in place because it kept screwing itself farther in and causing the car to idle up. I have my tip unscrewed as far as it will go so the car idles around 700 rpm and the cams sound aggressively choppy despite being stage 1's.
But could this cause the surging
 
Yeah so I cleaned the egr yesterday fully and never really ran it but I ran it today for a bit and it idles now around 1k rpm and doesn’t surge maybe the egr needed to be cleaned out and it runs much smoother now
 
Sounds more and more like an IAC issue. Especially since you said it changed a bit when you swapped them over. Try removing your IAC and turning the tip counterclockwise a couple turns. It should idle down. I'm on my 4th or 5th IAC because of idle issues. I ended up removing the tip and putting Loctite on the threads to hold it in place because it kept screwing itself farther in and causing the car to idle up. I have my tip unscrewed as far as it will go so the car idles around 700 rpm and the cams sound aggressively choppy despite being stage 1's.
Hey man so I cleared codes and o2 sensors will not be ready again I’ve been driving it but still still says inc it was ready before.
 
when you clear the codes it resets the monitors meaning you have to redo the drive cycles.
 
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