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Discussion Starter · #1 ·
So it's been a few months. I've read all the forums. And I know alot of us have dealt with this issue.

What it's doing:
When you start the car anytime it idles or you hold the pedal around 1500-2000 rpm the idle surges pretty fast up and down. About 300 rpm back and forth. No slow surge. Super fast. Between 1500-2k rpm moving about 300 rpm up and down. Now keep reading before you give me ideas.

Want to note car drive amazing when accelerating and decelerating. I've been driving it around. But if I'm cruising or idling in that rpm range I get that surging. When I'm driving tho it jerks the whole car BAD.

Whats on the car:
Car is a 2000 lx sedan (is manual swapped <not by me>)
1998 d16y7 motor (has a y8 thermo housing No idea why)
All the attachments around the motor are stock 99-00 d16y7 parts.
Oem auto wiring harness.
P2e a12 ecu (2000 d16y7 manual)
Pretty much oem all around

Whats been done:
I've replaces everything accept the water pump for cooling. Flushed the system many times. Changed all sensors. And thermo.

Replaced every sensor that reads air and pressure and stuff like map sensor and replaced tps

Iacv is working properly.

Ground is in good shape

All wiring is correct.

No vaccume leaks.

So now I'm left to believe it's something fuel related. Maybe the wrong injectors from previous owners. Maybe regulator. Not the ecu it's new. I've been through everything twice accept the fuel system. But I did check injector o rings. Those are good. All sensors I've check they're reading right. I'm at a loss and need some help and advice on which direction to look to.

Also wanna not compression is a 175psi accross the board.
 

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OMG TOTALLY COOL TITLE!!!!
88 y49 crx
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3,908 Posts
have you messed with or is the idle screw on the throttle body adjusted properly? had a similar issue on a hatch i had. replaced everything as well. one day by chance i messed with that idle screw.... idled solid at 800rpm ran perfect there after.
 

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4d EG manual rack/trans low n slow
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179 Posts
Does it do this while driving, or only when idling? If the throttle set screw is misadjusted like si-hatch86 said it could cause the IACV to "hunt" for idle speed. Try loosening it and see if the idle mellows out.
Did you remove and clean the IACV? is the passage clear?
I've had a couple of cars get oil into the passage and gum up the seat for the valve, making it surge also.
 

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93 4d lx, z6,ported, port matched, compression bumped, balanced, manual swap
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1,260 Posts
What's the fuel pressure at koer, with and without manifold vacuum applied? What does pressure read when pump primes before starting? Has the pcv valve been changed? What does your tps read at idle? Does it wander around at all?
 

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Formerly weebeastie
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What's the fuel pressure at koer, with and without manifold vacuum applied? What does pressure read when pump primes before starting? Has the pcv valve been changed? What does your tps read at idle? Does it wander around at all?
I'm going to second all of that, most specifically what voltage is on the TPS at idle. Have you back probed the TPS wires to see what voltage is throttle closed and 100% open. I'm thinking it's most likely TPS adjustment related if it's doing it going down the road. What do your spark plugs look like? Pull one, take a picture of it, that'll help us understand if its fuel related.
 
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93 Civic HB SI, 95 Civic HB CX
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he said "no vacuum leaks" lol

did he remove the battery cable and let it sit for an hour, then do the idle re-learn?
Lmao. Number of times I've heard people say "i've checked for vacuum leaks, there are none", so i spend time chasing other rabbit holes, only to find out they don't know all the places vacuum leaks on these cars lol.

Rule number 1 in diagnostics, if someone you don't know tells you they've ruled something out, check it again haha
 

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93 Civic HB SI, 95 Civic HB CX
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So many forget that pesky booster, have to spray from underneath to get a reaction when using a combustible to test
Or in the car!

Using hose pliars, narrowed it down to the booster pretty quickly. Then sprayed around the booster outside, nothing.

Went in the car, and gave it a shot, found it.

Customer saw me shooting a spritz of brake clean up under the driver foot well inside the car (at the booster push rod area), asked me what the hell I was doing, responded with "you need a new brake booster."

He had spent close to 2 grand in shotgun replacing parts, over the course of 3 months. Took me all of 10 mins to find and about an hour to fix.
 

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Discussion Starter · #16 ·
What's the fuel pressure at koer, with and without manifold vacuum applied? What does pressure read when pump primes before starting? Has the pcv valve been changed? What does your tps read at idle? Does it wander around at all?
No idea about fuel pressure. But everything else has been done and reading normal. It has great pressure before started. I know because I cross threaded the fuel filter lol

I'm going to second all of that, most specifically what voltage is on the TPS at idle. Have you back probed the TPS wires to see what voltage is throttle closed and 100% open. I'm thinking it's most likely TPS adjustment related if it's doing it going down the road. What do your spark plugs look like? Pull one, take a picture of it, that'll help us understand if its fuel related.
Tps reads great. Plugs look great. Getting great spark. Timing is also spot on

he said "no vacuum leaks" lol

did he remove the battery cable and let it sit for an hour, then do the idle re-learn?
Yes I even did that. It was on another forum I read.

Lmao. Number of times I've heard people say "i've checked for vacuum leaks, there are none", so i spend time chasing other rabbit holes, only to find out they don't know all the places vacuum leaks on these cars lol.

Rule number 1 in diagnostics, if someone you don't know tells you they've ruled something out, check it again haha
You make a great point. I'll actually check for that tomorrow. And report back 🤝

I bet it was the booster and now we will never know 🤣
I'll check tomorrow and report back. I never thought about that. I feel like a dimwit being a mechanic myself. Lmao
 

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93 4d lx, z6,ported, port matched, compression bumped, balanced, manual swap
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Its one of the most commonly overlooked vacuum leak sources with the age on these cars now, easy to miss unless you intentionally test it specifically as the weep hole is dead on the bottom and there are usually too many rattles and sqeakes for it to be heard when its leaking in the footwell.
 

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Discussion Starter · #18 ·
Its one of the most commonly overlooked vacuum leak sources with the age on these cars now, easy to miss unless you intentionally test it specifically as the weep hole is dead on the bottom and there are usually too many rattles and sqeakes for it to be heard when its leaking in the footwell.
Welp. Sprayed brake clean all over the boosted. No revs. Sprayed inside. Nothing their either. But I did pump the brake petal and that caused the car to Rev up. Not hitting the gas. But then I made the surging happen and did it and it didn't Rev up or change anything.
 

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93 4d lx, z6,ported, port matched, compression bumped, balanced, manual swap
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Pull the booster line and cap it, see what happens, if problem goes away you know its something in the booster, if not start pulling and capping other stuff, like pcv, evap, fpr, ect. until it stops or you run out of stuff to pull and cap. This could be something like a stuck evap solenoid with a cracked line somewhere near the canister or something.
 
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