i am working on a 89 honda prelude 2.0 si. i have recenlt changed head gasket and resurfaced the head torqued everything to spec. i hav adjusted the vales no ticking idle really smooth but when im driving when i put it in to nutraul it wants to drop almost to wear it wants to dye then it shakes jus a lil bit tho and then back to normal idle and idles jus fine.

1st question is that cause by more going in (intake) or going out(exhaust)

2nd question is do have one of the cam trains too tight?

.004 for intake did them kinda snug

.007 for exhaust snug as well to the point where you kinda have to pull on the feelers to slide out of each valve.


please help me figure this out soon i have been trying to figure this out. any reply is greatly grateful.thank you

Mine does that too, the idle drop. I thought I also needed a valve adjustment. I'm curious to see what it might be, but I found out mine does that when the alternator is charging the battery and it idles rough and dips when the alternator is putting out power, weird.

yah but it wasnt doing that before i changed everything..it ildes smooth and no noise

.004 and .007 are just right. your valve lash is probably perfectly fine.

did you check/adjust the idle screw and ignition timing? and if so, did you actually do it the right way? lol, there is a right way and wrong way to do it.

no can you walk me through it..the right way?

the ignition timing is fine..

it also dips when turning the wheel and turning the heater/fan on it dips really low

definitely sounds like the idle screw and/or ignition timing are not set correctly.

1) warm the car up. then let it idle until the radiator fans have come on at least twice. turn off all lights and accessories and heater fan. keep the car running for the entire process below...
2) stick a paperclip into both terminals of the service connector; white plug in a yellow rubber boot in the far rear passenger corner of the engine bay just above the wire harness. check the dash, make sure the check engine light is on solid and not blinking. if it's blinking, do a normal code retrieval process, then reset the ecu and start over. if cel is solid, continue...
3) unplug the electronic idle valve, located on the front of the intake manifold just above the fuel rail. idle speed should have dropped a little bit when you unplugged it. check the dash, cel should now be blinking code 14. look at the idle speed on the dash...
4) adjust the idle screw on the throttlebody until it idles between 650-700rpms. if it doesn't get to that rpm, continue on to #5
5) remove rubber boot from timing cover on tranny. using a timing light, connected to cyl 1 or cyl 4 plug wire, check the timing. it should be pointing to the middle mark in the group of 3 on the flexplate. it should NOT be pointing at the T mark, that is the TDC mark for the timing belt. adjust the distributor until the pointer points at the middle of the 3 marks.
6) now go back and readjust the idle screw again until it idles at 650-700.
7) double check ignition timing.
8) plug idle valve back in, remove paperclip, shut car off. with ignition off and key removed, go to the underhood fusebox and remove the ecu fuse (pgmfi fuse), and the clock fuse. let sit for at least a full minute. put fuses back in. start car, let idle for at least 2 or 3 minutes. without touching the gas pedal. now drive it like normal.

yah but i found this on a prelude forum..
same issue
okay, some days it idles great. some days....not so great. What happens is that the idle fluctuates. When I press in the clutch it drops down, seems to stall for a second and then idles back up like normal. sometimes it just drops.

The idle adjust screw is the LAST thing you should look at or adjust! The idle speed is controlled by the ECU and set properly at the factory. There are no bolt-on mods that will affect idle speed. Only a valve adjustment, new TB, IM, blower, turbo, or internals should have an effect like this. Fix the root cause and you won't have to dick with the idle adjust screw.

Poor idle can be caused by a number of things. You should always check foro the cause in this order (order of probable cause):

- Old, worn plugs (replace)
- Old, worn distributor cap/rotor (replace)
- Old, cracked wires (replace)
- Valve adjustment (too tight will lower idle)
- Vacuum leak (check hoses and IM/TB gaskets)
- Air in coolant causing thermal valve to oscillate (properly fill & bleed coolant)
- Funky EGR valve (clean or replace)
- funky EGR port in manifold (clean)
- IACV dirty (clean)
- TB dirty (clean) --> remove MAP sensor first!!!!
- Dirty injectors (should send them to someone like RC to be rebuilt)
- Defective fuel pressure regulator (check for proper fuel pressure)
- Primary 02 Sensor (if fouled it can lower idle speed)
- Bent valves (do a compression test, then leakdown if bad, repair head if valves leak)
- Bad MAP sensor (try giving it a thwack w/a screwdriver handle)

If you have messed with any of these recently, start there first.

whats your opinion on this posting i found?

I know that post very well, and it's horribly horribly wrong in almost every way.
for starters, a blower or turbo will not have any effect on idle. secondly, a vacuum leak will RAISE idle, not lower it. dirty injectors also will not lower idle, unles they're so damn clogged up that they wont even flow, which is near impossible. for the fpr to affect idle, it would have to be stuck fully open or fully closed, also near impossible in a Honda.
map sensors almost never go bad in Hondas. and DO NOT EVER WACK A MAP SENSOPR WITH ANYTHING!!

and no, the idle is NOT completely operated by the ecu. there is an idle screw for a reason, and it is the SECOND thing you should check and adjust at the same time as ignition timing whenever you have a low idle. the first thing to check is the tuneup; valve adjustment, plugs, wires, cap, rotor. a bad cap and rotor will almost never affect idle though. the ecu is only capable of operating the idle speed properly if the idle screw and ignition timing are adjusted properly.

honda recommends that you dont touch the screw

I believe this is incorrect. You need to set base idle to 550 +- 50 after warming up the car and unplugging the iacv. When you reset the ecu it will bump up the idle to 750 +- 50.

The first white line after 0 is 500 not 200. A lot of people don't realize this.

OP, was your car idling fine after the engine work but before you adjusted the valves ? If it did, then obviously you're not doing the valve adjustment correctly. I would just bite the bullet and take it to a mechanic.

the ignition timing is fixed at any rpm below 750 as long as it reads 0% throttle and manifold pressure is accurate for idle, and is fully warmed up and service connector jumped. so no it doesn't need to be 550 +/-, only needs to be 650-700. but because timing is fixed, that means you can do it at 550 if you want too lol, it'll provide the same outcome.