Jimi Hondrix

1995 Civic EX with n/a JDM B20b engine. LS manual transmission, A/C, 85k miles. P75 intake manifold, OBD1 ECU. Purchased used four months ago ..prior owner did engine swap and automatic to manual transmission replacement.. Engine was leakdown tested, compression tested and block tested (all passed) prior to purchase. Engine has IACV only..no FITV.

I've read through several hunting/surging idle post here, other honda forums, article and videos. From what I've read causes of hunting surging idle include
1) air in coolant system
2) vacuum leak
3) worn throttle blade bushings
4) TB gasket leak
5) TPS voltages out of spec
6) dirty or failed IACV
7) Dirty throttle body
8) failing/failed MAP sensor
9) faulty ECT unit
10) faulty o2 sensor
11) Cogged PCV valve
12) incorrect idle screw adjustment

My engine's surging/hunting idle is as follows: at operating temp it starts during deceleration (at 1,200 rpm) towards and to a full stop. At full stops it idles from 1200 to 1000 rpm wih slight surging then, a few second later idles down to 700-750 rpm. From this point it will occasionally shudder and drop to around 500 rpm very briefly then surge back to 750 rpm. On hot, humid days it will idle high around 1200 rpm during deceleration and full stops..until lightly tap the gas pedal and rev engine a second or two..then idle drops to 750 rpm.

I've disconnected the IACV and idle drops very low (below 400 rpm).
Bled out as much air as possible from coolant with car on jackstands, climate control on max heat, fan off.
Removed and cleaned IACVand Throttle body
Replaced TB gasket (OEM).
Sealed vacuum leaks and no additional leaks found.
OEM PCV valve rattles..cleaned it with brake cleaner
Previous owner replaced o2 sensor a year ago

A very knowledgeable Honda dealership mechanic on a another site suggested it's most likely worn throttle blade bushing..can cause flap to stick or not close properly. He suggests replacing with a used TB from salvage yard.
All suggestions/repsonses appreciated

Jimi Hondrix

bump please.
Admin. can this post please be moved to 92-00 section?

kingofbattle909

iTrader: (6)

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1999 Civic Si

I had a similar issue on my Em1, it was random and would sometimes idle around 1500-2k other times it would idle normal, sometime blipping the throttle resolved it and other times it made it worse. Finally it just started idling at 3k rpms after driving it around and would never go down to normal unless I shut the car off and restarted it and then it would start acting up again after driving. You could also grab the throttle shaft by where the throttle cable connects and wiggle it around and make the idle go up and down depending on which way you moved it. What finally resolved my issue was replacing the throttle body with a brand new one, I also put a brand new tps gasket on it and a new map sensor o-ring.

Jimi Hondrix

Thanks. Pretty sure that's where mine is heading as well.