1995 Civic EX Coupe with JDM B20b. Manual transmission.80k miles on engine (supposedly). P75 obd1. Purchased car four months ago.

Intermittent high revs on deceleration that is getting worse as ambient Florida temps get hotter. I purchased the car in January and it had this intermittent high rev and hunting idle issue during the test drives. I was concerned about it before purchase but figured worse comes to worse..TB swap. Within a week of purchase I removed and cleaned the IACV (no FITV on this engine) and throttle body with CRC TB cleaner. Also, replaced the IACV gasket (old one was very flat). I also removed the throttle cable from the perch mount (middle of U-shaped bend) as it seems to make the throttle cable stick a bit. Other than an intermittent hunting idle (between 700-1100 rpm) the high rev issue was gone ..until a couple weeks ago and it seems to be getting worse the higher the ambient temps and humidty become.

Two weeks ago I pulled the TB off again and it was still very clean so, I know there isn't any sticking going on due to carbon buildup. The throttle cable looks to be working well when I test it with engine off and while idling, helper pushes gas pedal while I watch and listen for blade (butterfly) closing. I've yet to test the TPS sensor and reluctant to adjust the TB return set screw or idle screw. This intermittent high rev has become a safety issue during driving..I can blip the gas pedal and the high rev will then drop to a normal idle but, it's frustrating and not a resolution. I was told that as that the TB butterfly shaft can become worn which may cause the blade to be out of position and not return correcly to the full closed position.

Also, if I do replace is the current 60mm TB ..would going to a 68mm be an issue? Are Skung2 Alpha TB's good?

 

Ensure some slack on cable, ensure coolant is bled, reset ecu and relearn idle

 

Thanks. I did those items the first time I removed and cleaned the TB and IACV.
I pulled off the road today when the high idle occured and I twisted the throttle pulley manually to closed poistion and it brougt it down to normal idle. So, the butterfly is stopping just short of fully closed position. I loosened the spring nut and used synthetic grease on the the mating area of the stop screw and throttle pulley and that helps but, not a 100% fix.

I could adjust the stop screw down very slightly and see if that prevents it from catching yet, without effecting normal idle. I have a feeling that the butterfly shaft is worn and doesn't pivot as straight as it should. Also, have a feeling that TB replacement will be the resolution but a used one may come with the same issue. A new skunk2 68mm is reasonably priced but, from what I've read the additional size of bore compared to stock (60mm) decreases hp and torque below 4k and a slight increase in hp and torque above 4k rpms.

 

Possibly,

 

Today I removed the TB pulley and spring and I can see and hear the bottom part of throttle blade hitting the bore. There is some play in the blade shaft and with the pulley and spring if I lift the (pulley) side of the shaft while pushing the blade open with my fingers it doessn't scrape the bore. For a temp fix I used synthetic grease on the bore walls, greased the spring and the area where the blade shaft exits the bore.
Before I purchase a replacement I will use 320 or 400 grit and wet sand the edge (outer circumference) of the blade. I may use 600 grit and very lightly sand the bottom of the bore as well. I know I want to take as little off as possible to not effect air flow/idle yet, prevent the blade from sticking. It may not work but I feel it's worth a try before purchasing another one.

 

It should just rest on the bore not slam into it. That is what the stop screw does. This should be factory set but if there is a lot of wear it could be a problem.

My first guess would be sticky cable though, since you have noticed exactly that. A new cable is not expensive.

 

How exactly in detail did you reset the ecu?

 

Previous owner replaced the throttle cable just over a year ago..cable is working well, The bottom part of the blade is barely hitting the bore..stop screw is adjusted correctly Do you know if it's a bushing or ball-bearing that the thottle blade shaft pivots on?

 

disconnect negative terminal from battery
drain residual charge by switching on hi-beams headlights and pressing brake pedal a few times
turn of all electronics
reconnect negative terminal to battery
start car and let idle 15 minutes (all electronics still off)