Another Idle/rpm Question...
 

I haven't checked it out yet, but before I even start thought I'd get other opinions.

Say I'm sitting in Neutral. I press the gas just enough to raise my rpm anywhere from 1300 - 2000rpm, once it maxxed out, the rpm would drop back to 800 and then back up.. If I press the gas to jump the rpm above 2k, no problems.. This happens when driving too, so if I'm in second gear and I'm pressing the gas to raise my rpm in the above range, once it maxxes, boom jerks as if it wants to drop back down to 800+-... If i keep pressing the gas, no worries, but I noticed this today when i was stuck in traffic and gettin annoyed.

Any ideas? I was thinking air in coolant..

ok let me just make sure I have this straight in my head...

your stopped

your idling at around 800....

you raise the RPM to between 1300 and 2000 rpm with the acclerator (still stopped)

you release the acclerator and the rpms drop to 800

the rpms then go up on the own past what normal Idle should be?

and the rest of that I didn't get....

so do I have that part right?

your explanation is over my head.... I didn't get the second part. I got the first - you rev, no problem.... you rev higher - no problem. But the part where you are driving and something maxes out?????? take it from the top on that part and be clear on gear, vehicle speed, clutch engagement, throttle position.... you know the important stuff.

Off the top of my head - H22A uses a MAP as well, right?

IMO, this sounds like a tuning issue with the computer program.... I would have to say try a stock program before you go any further diagnosing this.

Ok sorry.. lemme try this again..

when u press the gas pedal just a little, it'll only raise the rpm so much. just touching the throttle will raise the rpm to say 2K (maxing out).. so If I press the pedal just enough to get the rpm between 1300 - 2K, once it can't go any higher without giving anymore gas, it cuts off and drops down to 800 and then back up and repeats..

^^^ that same thing happens in gear, except the rpm can't drop too 800 while in gear that's why it jerks as if the fuel just died, so car starts slowing down, until i give it more gas to raise it up again.. It's really weird to explain. It doesn't matter what gear, what speed, as long as it's between that rpm range.. Mind you I couldn't get past 3rd gear so I don't know.. but the jerkiness between 1st and 3rd was a lot less, assumin cuz heavier gears.

Generally in your car when you let go of the gas it just slows down smoothly, this is really rough.. how to explain.. hmm.. say your in first gear and you rev up to 6K then let go of gass then press it again.. it should be really jerky at that point.. same kinda thing..

Bruno, after like 20 mins it went away. First time Its happenned.. I'll see if it happens again.. I'll check the main things that control idle when I get the chance..

Ohhhh... so you can't like cruize at 2000 rpm (holding the throttle) in second gear for example w/o getting jerked around.

You are right, the higher gears would jerk less...

Let's think about this: it can be an engine or a driveline problem... but since you tested each gear 1-3, it would indicate it's not the driveline... then engine mounts COULD be suspect, but then again prolly not cuz they are just translating what the engine is doing. So we come to the engine... you said in neutral you can rev and hold the RPM no problem, right? Does this do it in open loop or closed loop (cold or warm engine or both?). The diff between revving free and under some load is the VSS now reads > 0 so a few extra sensors kick in. I don't have a Prelude manual, but read two sections of the Chilton. One is the Fuel Injection/ECU section, and the other is the Driveability and Emissions section. Look for the sensors that operate ONLY when VSS>0 and then test each of those. The MAP sensor can easily cause this, but the MAP is also involved in free revving the engine... however, the problem may be there under no load as well, except since it's not going through the driveline you may not feel it. Also check for a vacuum leak using a vacuum gauge.

First part is right.. holdin the rpm will cause me to get jerked around heheeheh..

It does it in neutral as well Bruno.. It's not the jerking i'm talking about.. the jerking is happening cuz fuel is being cut off when rpm maxes out in that range and im in gear(under load).

In Neutral, if I gas just enough to get between 1300 - 2K, once it hits it's max rpm for that much throttle the rpm will start fluctuating down and up from 800rpm - to whatever rpm i was at.. In gear it wants to do the same thing but can't because the car is in gear. The jerk is that sudden lose of fuel. Like a sensor is deciding to shutdown.

I'm gonna do a quick coolant bleed first, cuz i had a little leak a few days ago on my coolant output line when a clamp decided to loosen up a bit. Move onto TPS curve and so on..

I'll check if it's happenning at lunch in an hour or so. It's probably not as cold as it was sitting overnight.

so it does it warm AND cold, right?

if it's doing it while cold as well, then it cuts down a LOT on the number of sensors you have to check out - like MAP, TPS, and engine coolant temp sensor.... but the ECTS wouldn't cause that, which would leave you to the MAP or TPS.

I really am not sure if it was doing it when the car was cold.. I'll find out sooon enough!

Thanks for all the input :)

Came back from Lunch.. Didn't do it.. I'll see if it does it going home tonight..

Mine shows low RPM as well on idle, but it idles fine..... I'm pretty sure in my case its just the tach wiring. I'll find out as soon as I wire together my Vafc II.

In most cases, try adjusting the idle screw.

Idle screw is fine, otherwise it would be fluctuating without me touching the throttle.

actually, it wouldn't fluctuate b/c of the idle screw unless you got a midget under the hood playing with it all the time. :D

damn Gremlins.......:p

if your idle screw isn't set right it can.. That was one of the problems I had with the swap REMEMBER?! heheh.. the idle screw was open too far and the idle just kept going up and odwn up and down..

Well, like I've said many times before, the idle screw should never ever be touched unless the throttle body is replaced with a new unit.... but if it's already been fuct with then blah... all the idle screw does is allow a metered amount of air into the intake past the throttle body when the plate is closed. What I was saying is the if this is as it should be from the factory, there is no way idle will fluctuate based on the idle screw adjustment - the amount of air getting past the closed t-body is fixed.... well, I'm sure you understand my logic.