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420A Weird idle Help!

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Seth Schneider

Probationary Member
19
0
Aug 15, 2018
Botkins, Ohio
okay i bought this car as my first car a month ago but it had a high idle, 3500 to 4000, anyways the previous owner said to just turn the car off and pull the actual throttle on the tb full throttle and let go and it will go away, and sure enough it did, and he said it only does it when you mash the gas pedal. also when you tap the gas the car revs up but takes longer to get back down to idle speed it’s not super slow but it’s noticable, also me and my buddies took it for a spin the other night and it did the high idle again and i did the same thing and it went back down, any help would be appreciated. Thanks!
 
i unhooked the cable and it still does the same thing where it takes longer to get down to idles speed, any other ideas?
Check and make sure the throttle closes. Physically push it by hand. If it wasn't closed you and you can close it you have a dirty throttle body, improperly assembled unit or something physically bent or broken.
 
i’ve been in a loss for words i’ve taken the tb apart and cleaned it (it was filthy) i cleaned the iac sensor and replaced the tps sensor, it hasn’t changed anything at all. today i got the idea of unplugging the tps and seeing if it changed anything, it used to be right when i touched the throttle it went up super fast and jumped to 2500-3000 but now it was super smooth if i lightly tapped the throttle, and then plugging it back in caused it to jump up rpms aggressively with a tap of the throttle. any advice would kick a**.
 
I'm new to dsm's I've been in hondas all my life and I just got my first one it's a 99 gst eclipse and it idles rough and I noticed that there are 2 holes drilled one on the head right in between the cams and the other in the intake tube (which I figure might have been for nitrous with the previous owner and u cant get ahold of the previous owner anymore and u cant figure out what the hole in the head between the cams is for or if the previous owner did it on purpose to ruin the motor. Does anyone have any ideas? And sorry for boosting the thread I cant find the spot to add a new thread.
 
@Seth Schneider sound alike you found your culprit of a bad TPS.

@Chim-chim you'll have to show pics of what "holes" you're talking about. Sounds like the spark plug valley drain hole and.... something else. Post a couple pics of the exact locations you're referencing.
 
@Seth Schneider sound alike you found your culprit of a bad TPS.

@Chim-chim you'll have to show pics of what "holes" you're talking about. Sounds like the spark plug valley drain hole and.... something else. Post a couple pics of the exact locations you're referencing.
yes but i bought a new one and it didn’t change anything.
 
yes but i bought a new one and it didn’t change anything.

Have you checked/tested values for the sensor? I skimmed the thread, but test what you're getting on the wires compared to factory. Sounds like you're getting a signal crossed or have a bad input voltage to the sensor.
 
This is a hole drilled would anyone know if it suppose to be for something or someone messing with the motor
 

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Yes you can drive the car with the IAC unplugged. But the ecu now has no control over the idle speed. On cold starts the car may idle a little lower then normal. Also the AC and heavy electrical loads will effect the idle speed. I would replace the IAC or at least test it.
 
alright i know it’s been awhile but i’m still having annoying problems, the cars idle still hangs a little when i rev it and i’ve changed the iac and tps, and it still idles super high if you mat the gas pedal all the way when driving so i still have to go to the throttle plate itself and pull it full throttle and flip it back, the other day i went out and started it because it hasn’t ran in like a week so i got it warm and then went for a drive and came back and everything was still normal until i revved it and it got past 3k and just stayed there, i turned it off and turned it back on and it was all good again. i noticed when starting the car the idle is a little bit higher like 2500 and then it goes down , also coming to stop signs when i push in the clutch it just stays at 2k or higher and not idle speed, and if i shift from 1st to 2nd below 3500 the idle will hang until i let out the clutch, none of the other gears do this. these problems are so annoying and i just want it fixed and no one can help me.
 
FWIW- I had similar obnoxious issues after switching to a 1g NA TB. Changed IAC for known good unit, no dice. Installed a FIAV bypass plate, kept IAC,all problems are gone. Have not looked back since. I dont have much more on it than that
 
FWIW- I had similar obnoxious issues after switching to a 1g NA TB. Changed IAC for known good unit, no dice. Installed a FIAV bypass plate, kept IAC,all problems are gone. Have not looked back since. I dont have much more on it than that
can you explain the FIAV bypass plate? and would the idling super high after mashing the gas be solved to?
 
I don't remember off hand whether a 420A has a FIAV (fast idle air valve) or not, it's been a long time since I owned one. But, I can tell you the TB's on the 4G63 and 420A are completely different. If you don't have a vacuum leak somewhere else I'd say your throttle shaft seals on the TB are probably shot. Do they make a rebuild kit for a 420A TB? If so, I'd buy one and completely rebuild it make SURE the kit comes with throttle shaft seals - not all of them do. Between a rebuilt TB, a new TPS, and a new ISC, you should have your problem solved. If that doesn't do it - your probably is elsewhere.
 
I think you have a vacuum leak some where. Usually when the idle air control (IAC) motor starts going out on 420a cars, the car will die when your coming to a stop, most notably right after you exit the freeway.
make sure that your pcv valve isn't stuck open
 
what is an isc? is that like an iac, and i’ll look into rebuild kits, i forgot to mention that when the car is idling really high after mashing it the throttle plate was about a half inch away from where it’s supposed to sit at idle. i pulled off the tb a couple months ago and it was terribly filthy so i gave it a good clean.
 
i’ve been wanting to check for vac leaks but haven’t had time i was planning on going out and checking for them tomorrow i guess i’ll let you guys know how that goes, thank you for the help hopefully i can get this fixed.
 
unfortunately couldn’t find any rebuild kits but did i’m going to order a new throttle body and i found out why my egr is throwing a code, one of the prongs broke off and is stuck inside the connector.
 
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