[ZippuDoozy]

Recently did a dpfi to mpfi swap on my 90 DX Civic hatch. Got it running. Things are good. Everything came off a d16a6. With the TPS sensor plugged in, it runs great, idles right. Then the second any throttle is applied or after sitting for a good minute, the idle surges up, then down and almost feels like it's gonna die.

With the TPS unplugged, everything seems to run a lot better. It just idles at 1400rpm-1500rpm.
which obviously isn't ideal.

Brand New TB and intake manifold gasket. All my lines I believe are hooked up right. I did switch the two pins on the TPS wiring as noted in most guides.

Kinda at a loss here, as it runs fine besides the slightly higher than ideal idle when the TPS is unplugged.

Could this be a bad TPS, bad throttle body as a whole? Any help would be great.

 

[Rexinre]

Most likely a vacuum leak. Hook everything back up as normal (your TPS)... Get a spray bottle with water and spray around everything you modified one thing at a time. Start by the intake manifold gasket, if the motor levels out or bogs down you found your air leak. Sometimes water will seal the leak temporarily making the motor stop surging; if it's a really big air leak then water will get into the motor and bog it down a little. I've done this myself and found my bolts weren't tight on my intake manifold, I wrenched them down a little and the surge stopped.

 

[ZippuDoozy]

Most likely a vacuum leak. Hook everything back up as normal (your TPS)... Get a spray bottle with water and spray around everything you modified one thing at a time. Start by the intake manifold gasket, if the motor levels out or bogs down you found your air leak. Sometimes water will seal the leak temporarily making the motor stop surging; if it's a really big air leak then water will get into the motor and bog it down a little. I've done this myself and found my bolts weren't tight on my intake manifold, I wrenched them down a little and the surge stopped.

It's just weird to me cause it runs fine with the TPS plugged in until you give it any sort throttle (this is while sitting in neutral). Then it just surges. I took a video. Not sure where/if I should upload it to better explain the problem. I'll try spraying everything down when I get home though.

 

[EFB055]

Youtube and share it here?

It's probably running better without the TPS because when it's plugged in it's giving a bad reading. Either because of a bad sensor, or because the wiring needs attention. From memory it'll drive fine without the TPS hooked up until you hit around 3k rpm and then it'll fall on its face until your revs drop below that again.

The idle may be a separate issue.

Check continuity on your wiring from the plug to the ECU. Double check the pin locations. Double check the colours of the wires are in the correct location in the plug. Make sure you are looking at the plug in the same orientation as the diagram (from the back of the plug instead of the front of the plug for example) and make sure you haven't got the plug mixed up with your MAP sensor.

 

[ZippuDoozy]

Youtube and share it here?

It's probably running better without the TPS because when it's plugged in it's giving a bad reading. Either because of a bad sensor, or because the wiring needs attention. From memory it'll drive fine without the TPS hooked up until you hit around 3k rpm and then it'll fall on its face until your revs drop below that again.

The idle may be a separate issue.

Check continuity on your wiring from the plug to the ECU. Double check the pin locations. Double check the colours of the wires are in the correct location in the plug. Make sure you are looking at the plug in the same orientation as the diagram (from the back of the plug instead of the front of the plug for example) and make sure you haven't got the plug mixed up with your MAP sensor.

I don't believe I touched anything TPS related except extending the three wires and switching the outer pins around as everything says the TPS works opposite of the one on the DPFI setup.

Car runs fine with the TPS unplugged (minus check engine light and idle being around 1500).

I've driven it plenty like that so far, and it drives phenomenal. Can hit redline. Cruise on the highway just fine. Just, as stated, when stopped the idle is high. But it doesn't surge! Lol.

Here is the problem with the TPS plugged in

 

[Evanguy]

Id bleed the coolant system again. The idle issue may be a air bubblr near the iacv. Ive seen it personally a few times. ( edit this would be surging idle, so this may not be it)

Also what can happen is when you changed the IM the iacv may have got some dirt in it.

 

[ZippuDoozy]

Id bleed the coolant system again. The idle issue may be a air bubblr near the iacv. Ive seen it personally a few times. ( edit this would be surging idle, so this may not be it)

Also what can happen is when you changed the IM the iacv may have got some dirt in it.

You know, I was thinking. Maybe when I switched everything out (you're about to call me stupid, I know) I just reused all the old coolant lines that came off the d16 I took everything from. It idled fine plugged in AFTER the system was bled, but on any decent kinda rev, it would start the surge. Perhaps maybe there's splits in the old line that are pulling air in when it's under throttle and causing that to be the case.

I definitely value what you said too, about the dirt getting into the iacv while disassembled. Would I be better off (even if it's not related) just buying a brand new iacv?

 

[Rexinre]

It's just weird to me cause it runs fine with the TPS plugged in until you give it any sort throttle (this is while sitting in neutral). Then it just surges. I took a video. Not sure where/if I should upload it to better explain the problem. I'll try spraying everything down when I get home though.

Watched the video, again it sounds like a vacuum leak. What was the end result of the spray down test? Also, as mentioned above try and get all the air out of your coolant system as well.

 

[EFB055]

I don't believe I touched anything TPS related except extending the three wires and switching the outer pins around as everything says the TPS works opposite of the one on the DPFI setup.

Car runs fine with the TPS unplugged (minus check engine light and idle being around 1500).

I've driven it plenty like that so far, and it drives phenomenal. Can hit redline. Cruise on the highway just fine. Just, as stated, when stopped the idle is high. But it doesn't surge! Lol.

Here is the problem with the TPS plugged in

I had a similar pulsing idle issue, removed my IACV, gave it a good brake clean (NOT degreaser), replaced the o ring and the problem went away.

Or if you have a spare IACV, throw that on.

 

[ZippuDoozy]

So. The small hole inside the TB that I'm assuming is the port for the iacv. When plugging that a little with the intake tubing off with my finger, it levels out and sounds great. It shuts off entirely if I plug it completely. Would this be a bad iacv?

 

[Rexinre]

You have a picture of it?

 

[ZippuDoozy]

You have a picture of it?

Picture of what? The small hole? I believe it's the only hole inside the TB on the outer side of the throttle plate that moves.

I took the iacv off. The little figure 8 gasket looked pretty flat and like it was sitting low in it's seating.

Apparently, they're special order. Nobody for 500 miles has one in stock. So, I ordered it.

In the meantime, I put a VERY small amount of gasket sealant around the gasket to kinda help it seal a bit better till the new one gets in.

It seems to have cleared my problem up for the most part. Occasionally it will surge again (I can't recreate the conditions in which it does this, so idk) but will level itself back out after a second.

I'm guessing it isn't doing the best job sealing, but it's doing a better job than it did before.

Hopefully, when the new gasket gets here it'll clear my problem up completely. If not, I'll buy a new iacv and go that route. If the problem still persists, I'm sure I'll be back here with another thread lmao.

 

[Rexinre]

Good Luck.

 

[Paterico]

Sounds like a bad IACV.

FWIW, you don’t even need to use the coolant lines on the IACV. I took the plate with the coolant barbs off of mine so I could remote mount it. No issues.

 

[drtalon123]

If everything runs fine off idle, and you plug the hole with your finger on the inside of the TB and it dies, it's 'probably' not a vacuum leak, and more likely just ingesting too much air from the number of air control valves, but don't rule it out right away. Try to tackle vac leak testing first.

Spray around the intake area with throttle body cleaner or flammable non-chlorinated brake clean. When the vapors from the spray get near a vacuum leak, they are sucked in and the engine responds due to you temporarily forcing the engine rich. This will cause RPM to fall, which is the telltale of the spray being ingested by the engine through an area where it should be sealed. Remember, only spray around the intake and/or vacuum operated components in areas where there should be VACUUM, meaning if you spray around the intake with the TB wide open with no pipe attached, you could be drawing vapors into the throttle body end which will give you a false positive. Connect the intake pipe to the TB and point the open end away from vapors when testing to prevent this, especially if you are testing around your TB gasket. If you spray everywhere and you can't get idle to drop or stop surging the way it normally does in your video, you probably don't have a vac leak.

And for god sake, please don't spray on or around your distributor lol. The distributor cap is vented, vapors can get in and sparks are there Can't tell you how many times I've seen guys accidentally spray around a dist and POOF, a quick fireball lol. Harder to accidentally do this on Honda engines with the dist off to the side of the head, easier to do on older GM/Ford/Chrysler vehicles since the dist is typically at the front or rear of the intake in blind areas that are hard to not spray when testing. In either case, the danger is still very real and present, just a heads up if you've never done this before!

If you find you don't have a leak, then try two more things before moving on to taking FITV and idle control valve apart for cleaning.

1. You don't have a Check Engine Light on do you? Maybe there are wiring issues? You didn't accidentally switch around connectors like the MAP or IAC did you? Just food for thought!

2. Try lowering metered air by adjusting the TB bleed air screw, this one:



Your TB may or may not have a cap over this screw, hiding it. Turning it in closes the bleed air passage, loosening it opens it. Try turning it in a bit and see if surge stops. Go slowly, no more than 1/4 turn at a time, then blip the throttle valve and let the engine come down to idle. See if it still surges. Keep going and trying again to see if you can control the idle. If you end up bottoming out the screw or are past 2 full turns and you are still surging, check the FITV and IAC components.

 

[EFB055]

So. The small hole inside the TB that I'm assuming is the port for the iacv. When plugging that a little with the intake tubing off with my finger, it levels out and sounds great. It shuts off entirely if I plug it completely. Would this be a bad iacv?

Did you clean while you had it off?

 

[ZippuDoozy]

Everything was cleaned and reassembled. Put a new IACV gasket on, and adjusted my idle control screw on the throttle body following proper procedure.

Everything has worked great since and the MPFI swap hasn't given me any problems what so ever.