Just bought a 91 CRX Si. Upon starting it the engine immediately revs to approx 5,200 rps. The guy I bought it from said the sensor is bad (I apologize for not remembering exactly which sensor) (It is located in the back side of the TB and has 2 12mm bolts holding it on) and that he gave me a new one with it. Thing is I read on this forum that if you clean it out it tends to usually fix it. I did so but it is still doing the same thing. The "new" sensor he gave me is a bit different than mine. Instead of the hoses coming in from the bottom the new one comes in from the sides. Everything else looks pretty much the same. Safe to use? Any suggestions? Any help would be greatly appreciated. Thanks in advance!!!

 

***UPDATE*** OK, the Honda guys on Facebook swore it was the IACV was dirty causing it. Took it off and cleaned it no fix. Took the IACV off my son's perfect running 90 CRX Si and it continued to do the same thing. At a dead end here.

 

Fast Idle Thermal Valve maybe? Its located under the throttle body. Back side would be your Throttle Position Sensor.

 

Is there any way to test it?

 

There's a thread on here somewhere about em, it has a set screw type ordeal inside it once you get it apart. Alot of times they tend to back themselves out over the years and can cause a higher idle or bouncing idle if they are out far enough. With your engine reving that high it could be a combination of things such as that, vacuum leak, tps issue, and so on.

 

Lordy, Lordy what to do, what to do, This is what I've done so far gents. Inspected Vacuum lines and cannot find a leak, missing or broke one. My son has a good running 90 CRX SI so I took the IACV off it and put it on mine no change. Took the working throttle body off his SI with ICS attached and it made no difference. I cannot find a the "Thermal Valve" in order to check it. It idles up to 5-6K rpms upon starting. Unplug the IACV and it will idle bounce from 1500-2500rpms. Unplug TPS and it does nothing different one way or the other. Any advice would be greatly appreciated. If there is a way to upload a video for someone to see and hear I would be glad to do so to get their input. Thanks in advance.

 

Definitely a vacuum leak and a bad IACV. If unplugging the IACV results in 4000 RPM difference, something is wrong.

 

Ok new revelation. There is a valve sensor attached to the IACV. From what it is listed as is referred to as the Fast Idle Control Valve. I forgot to mention in the first post the ECU was flashing code 14 which said something to the nature of IACV unplugged, improper ground, etc.. That being said I have got the FICV half way off and noticed it looked bone dry like no fluids had passed through it going to the IACV. Any of this sound familiar to anyone? Thanks.

 

Well, cant be a ICAV because I took my sons off and put it on mine and it did the very same thing. His car runs perfectly. But yeah with the IACV plugged in it revs str8 to 5-6K and unplugged it just bounces between 1500 and 2500. It's weird and I'm about to pull my hair out :D

 

Let me REPHRASE that haha. Your IACV isn't working properly. It may not be 'bad' per say, but its not doing what it should be doing.

Let me try and think of something. If you have a FSM you could troubleshoot it. Have you tried swapping the wires on the plug? Or tracing them? Could be improperly wired or something.

 

Trace the iacv wires from the plug to the ecu. Make sure they are going to the right pins. You can find ecu pinouts on google.

Also, check throttle cable tension. Hell, unhook the throttle cable completely from the TB and see if it changes anything.

Are all of the vacuum lines on the intake manifold attached to their proper place? Check for broken/cracked hoses.

 

I totally forgot about the throttle cable. You could have an over tightened cable too. But the IACV is definitely malfunctioning.

IACV is A9 on the OBD1 ECU.

 

Read the forum Rules - "Help" is not an acceptable thread title.

 

My apologies.

 

Well, that kinda confirms my worst nightmare. I have swapped the throttle body, IVAC, TPS, FIV, checked all lines and routing. I tend to agree it may be in the wiring. It's a long shot but unhooking the throttle cable will be my last ditch effort and I'm sure it'll be on to wire tracing. :D Thanks for all your help guys. I'll keep ya posted.

 

HEy heres a question. does your car come with a MPFI set up, ie a SI trim level? or does it have a engine swap. say you baught a DX with a MPFI conversion? if this is the case perhaps someone did not swap the TPS wires...simply take off the wires on the ends leave the center wire in the plug and swap the outer ones. just a thought.

 

It's an all stock original 91' Si. A new note for today though. I heard someone mention the MAP sensor. Tried unplugging the vacuum line from it to see what difference it'd make. It revved to about 3K 5-10 secs came back down to 1k then started bouncing between the two then would die and not restart. It'd try to hit but would not start. Hooked the vacuum line back up and it was right back to 5K+ upon starting. I thought "hmmm" that's something it's not done yet. I took the MAP of my son's running 90 Si and tried it. Revved to 3K, held there for a few seconds then gradually kept going up and up to about 6K and I shut it down. Pulled the vacuum line off his and it just held at 3K. I am about set fire to this hussy. She's pissing me off but good lol.

 

***UPDATE*** ***FIXED!!!*** After much cursing, scratching head, swapping this and that I have finally solved the problem. It may be an interesting issue for future people who have the same/similar problem. To the very end it was throwing a code 14 which is IACV and from EVERYTHING I've read and by all accounts the way it was behaving it SHOULD have been the IACV. Well, in the end it was not! After a couple nights standing there in disbelief, can of gas in one hand and lighter in the other I tried putting a $14.99 Intake Manifold Gasket on it and VOILA, she now purrs like a kitten. Thanks for all the help guys and gals!

 

if it happens to someone else, air in the coolant system will cause this as well.

 

Saw that one coming

 

Lol yeah your problem was the intake manifold bolts weren't tightened. Happened to me too because I kept removing my manifold to get to the oil pressure sender and on firing upthe car it revd to 5k+ because I didn't tighten the bolts.

 

Lol, actually they were plenty tight. When I removed it (It had to be stock gasket) the entire length of the dip from one side to the other was missing completely. I am assuming fell out, chewed up internally or God knows what. Anyways, she is purring like a kitten. Even though it is running rather good I have a couple issues you guys might be able to help with. Quite a bit of smoke. Looks like blow bye but smells like it's running rich. I am going to put a tune-up on it over the weekend and see what happens.