Greetings. I have a JDM OBD1 B16A (stamped 1992) swapped into my del Sol that is now experiencing a surging idle after warm up. The surge is very minimal and happens between 1000-1300 RPM, and I can initiate it by merely tapping the throttle. What's weird is that I can stop the surging if I put a lot of pressure on the throttle body lever against the stop screw (which hasn't been tampered with). The car seems to drive nice and smooth, and VTEC engages properly, but after driving for 15-20 minutes the CEL turns on, and the idle surges at random after coming to a stop (meaning it will not surge at every stop (but CEL stays on)).

The idle issue began after I removed my IACV, FITV, and throttle body for cleaning, after finally realizing that my FITV was seized (no high idle at cold starts). I disassembled my FITV, cleaned the rust out of it, and reassembled it screwing the white plastic piece, not all the way tight, but about a half turn from being tight. Now my cold idle is where it should be, starting at <2000 RPM and gradually (and steadily) lowering until warm. I also cleaned the IACV with electrical connector cleaner, which didn't even look too bad to begin with. Additionally, I cleaned the throttle body and plate (more on this below), set my TPS (which I found was missing its bottom torx bolt) to 0.48v closed, burped the coolant as best as I could, and retarded my ignition timing two degrees (for a different, non-related reason). I even set the base idle to ~500 RPM using the unplugged-IACV method by adjusting the throttle's idle screw (as it was tampered with by the previous owner to where the engine would stall with the IACV unplugged). Keep in mind these are all things I did prior to learning about the surging idle.

As of right now the idle does not surge until the engine is warm and is only initiated by touching the throttle. Oddly enough, I've read that the there is supposed to be a type of paint or sealant right after throttle plate and on the plate itself to help seal it when closed, but being me, I just cleaned the whole damn thing with brake cleaner until it was silver again. There was this black layer, now that I think about it, that didn't come off like normal carbon when I cleaned it--it kind of seemed like a black paint that sort of flaked off and took extra effort to remove, but at the time I thought it was just carbon build up and rubbed it all off. I also did the test where I plug the holes inside of the throttle body leading to the IACV (top hole) and FITV (bottom hole) to check for suction. The bottom hole did have suction but didn't do anything to the engine when I plugged it (I'm going to test this again). When I plugged the top hole, the engine almost died (the RPM felt lower than 500). I believe the IACV is working because if I unplug it while the engine is on, it'll drop to the base idle I set it at, which is ~500 RPM (I did accidentally plug it back in while the engine was running and heard a "fwoomp" sound from the area).

So what do you suggest could be the problem? Have any other tests I can do to get more information? I'm starting to lean towards the throttle plate not sealing/seating correctly, letting more air in than it should. My next steps are to fully tighten the FITV adjuster and maybe tamper with the throttle plate stop screw (still has the yellow paint). Thanks for any input you may have.

 

Oh yeah, and when I try to pull the CEL codes, the CEL just flashes constantly. I can't tell if it's giving me a code 1 or 10 (the flash is like half a second and happens every 2.5 seconds). The ECU is for a D16Z6 auto but it's chipped so I don't know if that would interfere with the OBD1 code flashing function or not.

 

Post a video.

 

So, I think I got the idle to stop surging (for now).

I first went back to the FITV and fully tightened the white adjuster piece. After that I went ahead and did some more testing which involved resetting the ECU a few times, unplugging the IACV a few times, plugging the holes in the throttle body, etc. For the first run of tests, I pulled the ECU fuses, put them back in, and let the car idle until it dropped to 750 RPM (about 20 minutes of idling from cold to operating temp). I noticed that the idle at 750 was kind of rough--I'm not sure if that's due to being two degrees retarded or what. Then I turned off and immediately back on the car to officially reset the ECU, and so far no surging. Then I tapped the throttle body lever and the surging between 1000 and 1300 RPM began once more. I did the suction test in the throttle body for the FITV while the idle was surging but had no effect at all (though there was some suction through that bottom hole). I then unplugged the IACV and the idle dropped to around 600 RPM or so (with no surging), so I adjusted the idle screw to get the base idle back to around 500 RPM. I turned off the car, plugged the IACV back in, and turned the car back on, where there was then no surging. I then go and rev the engine at the throttle body and once again the surging begins, so I press hard on the throttle body lever against the set screw and the surging stops and idle drops to ~800 RPM. I take my thumb off the throttle lever releasing the pressure and the idle rises back up a little but with no more surging.

I get my multimeter and start testing the TPS. It reads 0.48v without the pressure on the throttle body lever, but when I put pressure on it, it reads 0.45v. At this point I turn off the car, reset the ECU, and restart the whole process again. I unplug the IACV again and adjust the base idle via the screw to get it at 500 RPM (again). Once again I get idle surging after I touch the throttle, and so what I did after turning the car off was let the spring tension of the throttle body lever slam the throttle plate (and set screw) a few times by releasing the lever a WOT--the plate actually got stuck closed once and I had to use the butt of my screwdriver to get it open. I turn the car back on and let it idle, and when touch the throttle, NO MORE SURGING. I did exactly what I did last time with the throttle body lever to get it to surge but it wouldn't. It would not even surge after revving high and letting go quickly. I turn off the car and put the intake back on and do the same stuff to try and get it to surge, but it would not (which is good I guess).

My next test is to actually drive the car and see if the CEL comes on and begins surging again. Unfortunately it began to rain while typing this post. I'm going to reset the ECU again to get rid of any codes too before my drive (which probably won't be until tomorrow). So could it actually be the throttle plate not seating and thus sealing correctly, making a sort of vacuum leak? Or is it something related to my TPS? The throttle cable is most definitely not over tightened.

 

I'll try. Basically, the CEL flashes for half a second, waits for a couple of seconds, then flashes again, and repeats this forever. There's no noticeable pattern that would indicate any code other than 1, if it's even that.

 

https://www.youtube.com/watch?v=vhK8...ature=youtu.be

This was shot (yesterday to be exact) before I got the idle to stop surging.

 

Took the car out for a reasonably long drive--more than an hour's worth. No problems worth noting for the most part (other than the idle (steady 750 RPM) not being the smoothest of idles (not sure if this is because I retarded the timing two degrees or what)). I drove in all kinds of conditions, like stop-and-go city and freeway @ 80mph. Also, I stopped every once in a while to shut the car off and on (to see if that had an effect on anything (which it didn't)), and I even did some mad pulls and hit VTEC (yo) a few times. HOWEVER, on my way home I got caught at a stop light that lasted a minute or so and like 30 seconds after I took off the CEL came on. Driveability didn't seem to be affected nor did the power. So when I got home I let it sit and idle, which was normal at 750 RPM, then I turned it off and turned it back on--the CEL went away and I decided to mess with the throttle body lever... After tapping it a few times I got the idle to stick at around 1000 RPM, however there was no surging. I couldn't get it to surge whatsoever. But I did press on the lever and that made the RPM drop back down (again), and after I let go, it rose back to 1K.

I did reset the ECU prior to driving and the idle took about 20 minutes from cold to operating temp @ 750 RPM (before I turned it off and back on to officially reset it). The FITV seems to be functioning correctly and I didn't touch anything or mess with any adjustments. So far this was the longest I could drive before the CEL coming on. What do you think could be going on? Is the throttle plate not sealing all the way and letting in too much air, screwing with the IACV's readings (and thus activating the CEL)? I haven't touched the set screw for the throttle body lever because it's still at its factory setting. Should I just say "screw it" and lower it to see if I can make the throttle plate seal more? Or is it something totally different?