B16a2/LS trans, 94 civic ex coupe factory auto, chipped p28

To start I have no CELs and no audible misfire just an occasional pop on decel, I’m chasing the last of my vacuum leaks my ideal idle would be 800-1000 but as it is now the car idles at 1500 with an occasional rise to 2000 after giving it gas or going into neutral at a stop. When I spray the intake manifold with brake clean the idle revs up, the last maintenance item I did was injector seals and while I was taking the injectors out I noticed cylinder one was missing it’s filter basket, on top of that the injectors just look beat so I ordered a new set of tested remanufactured 240cc injectors, on top of that I know my iacv has been faulty in the past and I’ve cleaned it numerous times, so I went ahead and ordered a new oem one. And finally the pcv valve is non oem so I ordered one to replace it and when i do I will replace and clamp all the vacuum lines for the pcv system. If none of that fixes it my last guess is to remove the intake manifold jb weld any cracks if there are any and reinstall it properly.




The injectors, iacv, and pcv get here next week, my main concern is am I on the right track or do you think I’m chasing ghosts im finally getting to the point where I can’t justify anything as maintenance everything is new and should be in working order and I feel like I’m missing something, does the idle need a hard relearn? I’ve gone through the pedal cable armature and made sure there’s no flex or stickiness. the previous owner had the p28 chipped so should I look into a rechip? I got a 70mm blox throttle body for free to replace the broken (improperly deleted pcv line) 68mm the previous owner installed but is that too much induction for a 1.6 even with an skunk2 pro manifold, 4-1 header and a high flow cat plus a yonaka? Other than the work I’ve stated in the first paragraph it sounds like my only other option is a rechip or hondata.

edit: what is the proper idle relearn procedure I know to reset the ecu, should the iacv unplugged or plugged, what should the idle screw be set to, I’ve heard to hold it at 3000 till the fans come on and I’ve heard just let it idle for 5 minutes what’s the best way?

 

Take the intake off and using your finger, you can diagnose what's going on. You'll have 1 or 2 holes in the throttle body before the plate. If you have 1, it's the IACV. If you have 2, the lower hole is for the FITV, the upper is for the IACV. With the car at operating temperature, plug one or both of the holes.

If the car is at operating temp, plugging the FITV hole should do nothing. If it does, readjust the FITV so it's closed fully, or eliminate it like most folks. I just noticed you have a skunk2 alpha throttle body it looks like (reading blox now lol), so you shouldn't have a FITV but I'll leave this here for the next Google traveler.

With the car at operating temp, plugging the IACV should cause the car to stall or almost stall. If it drops rpm but doesn't stall, you have a vacuum leak somewhere else in the intake system. Like your throttle plate isn't closing fully, adjust stop screw. Or intake mani not tight enough or gaskets failed.

If the motor stalls, good, the IACV is doing something. Likely stuck open. If you're here, try cleaning the IACV before replacing it. All those parts you want to replace, I wouldn't replace unless they are testing bad. If you swap in a new part and the issue doesn't change, go back to the old honda part, they just seem to last longer.

There is no real idle 'learning', the ecu doesn't have idle compensation trim tables. But the proceedure to set the idle would be start car, get to operating temperature, unplug IACV, adjust idle air bypass screw until idle is 700+/- 50rpm. If the screw can't get you there, you'll have to try the throttle stop screw. Adjust too far, and the throttle will start sticking. Once idle is ~750rpm you can plug the IACV back in and it should kick it up a little bit and idle normally.

The size of the throttle won't affect it that much, you could have a massive mustang throttle on there and I'm sure it would still idle down low enough when calibrated fine. If it's been tuned badly, that can make it harder. Someone could have jacked up the IACV compensation or set the idle target way high.

 

The fact that it revved up when you sprayed brake clean at the intake manifold, shows theres still a vacuum leak. And in the location where you were spraying. Unless youre saying you had a leak there and repaired it with the new injector seals.

 

Okay so I’ve talked to some other people made some progress. I put the new injectors and iacv in went to start it up car immediately goes to 3k scares me so I turn it off lol, call my Honda og with he advises me to let it idle out so I do that it revs up to 3 then down to 2.6 and back up typical air in the cooling system so I try to bleed it as it warms up and the fan never kicks on. Tested the fan, fan relay, and harness connector all are good so I’m gonna throw a fresh thermoswitch in tomorrow (autozone and they late *** delivery) and try to bleed it again. I’ve noticed in the past my hood steaming in the rain after a 10 min drive to work so I suspect fan hasn’t been kicking on for a while. My working understanding is if the fan doesn’t kick on ecu doesn’t know how to purge the air out of the iacv or something like that

While the car was running sprayed the intake mani down with maf clean to test the vacuum, and honestly nothing changed in the idle same with the tb and charcoal canister lines. That said the gap between my brand new master cylinder and booster leak like crazy the lines are good and the booster valve is the right way, I have the correct rubber circle around the piston and the piston was adjusted correctly. Honda og from earlier advises to pull it off a little and put a thin ring of permatex ultra black around the mc booster mating surface can y’all support that?

Also I was mistaken I pulled the intake off and the throttle body says 68mm on the butterfly valve so it’s not that ridiculous of a setup, one of the previous owners put arp head studs in it and chipped the p28. I honestly don’t think the chip is at fault because it’s idled under 7-9 reliably before but I have no clue what the chip is doing because vtec is still 5500, could be for obd2 to obd1 conversion because I run a single o2 sensor with no cel.

consensus will reply again when car is fixed or exploded and go through issues start to finish for the internet explorers

 

The line that I highlighted above is totally incorrect and the ECU has absolutely nothing to do with purging air out of the cooling system. Mother nature handles the purging of air from the cooling system... bubbles rise to the top, so the higher you can make the fluid surface at the radiator cap, the faster the circulating coolant will work the air out. This is why using a bleeding bucket works so well.

NEW TEST: Crank the engine and let it idle... once warm, perform the following: Remove the brake booster line from the intake manifold end and cover the open nipple on the intake manifold with your finger so no vacuum leak exists there. What does the idle RPM drop down to ? If it is at or below 1000 RPM, then you have found your problem. Fix/replace the brake booster vacuum leak that you have previously stated existed anyway. If the idle is still too high or "hunts" up and down, then place a vacuum cap over the brake booster hose port on the intake manifold (if this isn't available, use a short piece of snug fitting hose and plug the open end of the hose with a bolt that fits tight in the hole), and with the engine idling and warm, place the palm of your hand over the inlet opening of the throttle body - completely covering it. The engine should stall within a couple of seconds... if it doesn't, you know that another leak exists, and now you must find a way to discover it.

 

Thanks for all the clarification on how the cooling system works I am kind of a noob, thinking back when I changed the iacv it seemed dry so that’s likely the high point in the system where air is trapped so I will put a bleeder bucket on it tomorrow when I start it to do your test. As for the vacuum leak on the booster leak, one of the nuts holding the mc seems to be a cross threaded preventing a tight seal and I can’t take it apart so hopefully rtv will do the trick I know it’s frowned upon but I don’t want to spend a week taking the brake system apart for like the 5th time as I just got it working.

 

RTV on the booster worked, I sprayed different parts of the engine with brake cleaner and no change in idle. I can put my hand over the tb and stall the car now, so I can say thatI don’t think there are any more vacuum leaks, my main issue now is either air in the cooling system or something to do with idle screw and distributor timing because my idle is still 1500- 2500 as is and fluctuates based on what I do. When I unplug the iacv I can get my idle to 800 but it sounds like it’s lugging and when I plug it back in rpm shoots up. The whole time the radiator fan never kicks on and lower hose took a while to get warm, I’ve tried the bleeder on the back of the head and a bleeder bucket but I’m not to sure what I’m doing to be honest. Towards the end of the bleeding the radiator looks like it’s steaming crazy style but there’s not a noticeable leak when it’s parked and it rained outside before I did this and I splashed some coolant. My Honda homie gonna help me this weekend and he will probably show me what im doing wrong but I will come back with an answer if it’s found.

 

IACV sounds stuck open. Take it off and brake clean tf out of it. Usually that fixes that.

Yeah bleed coolant well. The fan should turn on if the thermostat fan switch grounds out, or the ECU can ground that circuit. Completing the flow of electricity for the fan relay, letting the relay power the fan. Good fuse and relay required. Lol

Best of luck. Good progress!