pulling on the iac does nothing. the computer knows and controls the position of the iac... d/c your battery made the idle come down, as long as there is no other 'leaks' or etc, it will stay like that. Note that the RPM the car trys to get at(manual) is 850 rpms

Neo: you need some type of OBD II reader, not just a code reader, but can read the outputs of the sensors of the car. i dont have a reader but the guy at advance auto has a 'actron II' which was able to get the data. goto your local autozone, advanced, etc and see if they can read the sensor information, not just codes. all you want to know is at idle, the IAC counts, MAP voltage(and mmHg or cmH2O), 'target' idle rpm, rpm, throttle % and voltage also not long term fuel trim and current fuel trim(at idle)

IAC at idle is usually 40-50 counts
MAP, not sure,
TP, should be at 0% or .40 volts, but i believe the computer can compensate for a variable of +5% or .51 volts (why it trends with the map sensor and 02 sensor information)


-T

Thanks for the info thomas. I'll look into getting that done at my local parts shop if they can do it. And maybe get me a print out and post it if possible.

As for what stephen was saying. I didnt know you can pull out that black plug part on the IAC sensor. I didnt touch it myself. I just replaced it with a new one a month or two ago.

Thomas, I still have to try the plugging the TB with my hand while it's running to see if it stalls to see if there are any air leaks else where. If not air may be getting past the butterfly valve.

ill update when I can.

Ok here's my story on this:

Car:
2000 Cav Convertible, 5 speed manual.

Symptoms:
High idle (1000 - 1500 RPM)
Once > 5 MPH the car would either (with the clutch in):
1) Bounce between 1200 - 1800 RPM like I was revving it with the throttle (which I wasn't)
OR
2) Shoot straight to 3500-4000 RPM and stay there.
However, once the car was <= 5 MPH the car would Idle around (1000 - 1500 RPM)

The crooked path to fix my car:
1) I replaced the IAC using an AutoZone one. --> Didn't work
2) Replaced the throttle body gasket and cleaned the throttle body. --> Didn't work.
3) Replaced the IAC with an O'Reilly one. --> Didn't work.
4) Adjusted the star screw because my tb was sticking. Didn't have the 'T15 torx plus security bit' (stupid overprotective chevy engineers), so I made it a slot bit with a Dremel cut-off wheel. --> Didn't work
5) Tested the vacuum and replaced the elbows coming off of the tb. All fine. --> Didn't work.
6) Screamed bloody friggen murder. --> worked to make me feel better
7) Bought throttle body / intake off of eBay for cheap. Installed new intake gasket. --> Didn't work.
8) Gave up and took to dealer. They found some non-insulated/heatshrunk connectors off of the PCM where the previous owner (God knows why) decided to splice into and changed his mind. They replaced these poor connectors and installed a new IAC. --> Worked and I promptly drove off into a massive thunderstorm here in the rainforest known as Texas.

Bottom line and new suggestion: Check your wiring before you assume a vacuum leak. The previous owner of your car might have been an idiot.

Thank you, have a nice day.

ryan, did you 'reset' your computer after doing the stop screw adjustment?

did you have a code thrown when it was messing up?

-thomas

I thought I'd add to this. I have a 97 Sunfire GT. I just rebuilt the entire motor. It started up on the first try. It drove great, and idled just fine(850rpm after warm up). Then all the sudden yesterday, I trash the upstream O2 sensor. I had a high idle at about 1500rpm after the O2 sensor trashed. I replaced the o2 sensor and had the parts house clear the error code. I still have the high idle. All the hosing and gasket are brand new and I have no leaks. I cleaned the motor excessively so there is no carbon build up anywhere. So here's my thinking on this whole topic:

Because I had a sensor fault, the car is running in open loop. When you cold start your car, your car runs in open loop. Open loop is default fuel maps and ignition maps programmed into the ecu that your car runs on until your car warms up enough to get proper input from your sensors. Closed loop is what your car is suppose to run in once your car is warmed up. In closed loop your car gets sensor input from your motor and programs the fuel and ignition accordingly. I don't think my car is entering closed loop. When you have a sensor fault, your car normally switches to open loop as it's not getting valid input from a need sensor to determine fuel or ignition. It's a safe guard. And in open loop, when you let off the throttle, your car idles down slower.

I'm going to reset the ecu by unplugging the battery for 8 hours while i'm at work tomorrow. If the idle returns to normal then I know it's an issue with the ecu. If it doesn't then it's a sensor issue. I'll also visit my friends at the dealer in the shop and have them get some reading off the car. Hopefully I can determine if it's the ecu or not. I'll post results tomorrow and hopefully a solution.

yea, chevrolet must use microsoft windows programmers for their ecu/pcm, have to keep restarting it after installing new hardware, or any error

but joking aside, unplugging it for 10 minutes is sufficient., unplug the battery, dont take out the fuse thinking that will do.

should work fine

-thomas

Thomas Sweeney wrote:ryan, did you 'reset' your computer after doing the stop screw adjustment?

did you have a code thrown when it was messing up?

-thomas

Yes, I reset my computer after each step. I didn't get any OBD II codes, but the dealer said I had some issues with the non-OBD II sensors they can read with their Tech 2 OBD II readers.

I have an ELM Scanner from scantool.net, but I somehow cannot find software to scan these extra sensors.

I got a little eager on this issue. I had unplugged the battery for about an 1.5 hour. I started it up from a cold start. Idled at 1100rpm. I'll be taking it out for a drive over lunch to let it heat up and check the idle. I'll also be stopping by my friends shop for some readings and see if there is any software updates for the obd II ecu.

argh. so i started the car up again and it popped on the check engine light again. It's still idling fine. I'm heading to the pars house for a read on the error code.

Ok here what mine does.....kinda opposite of high idle.
99 z24 automatic.

Start car...idles at about 1400.....
Car starts to warm up idle bounces from 500-1200. Never stalls. Sounds like big cammed V8.
When cavs up to normal temp....cav idles at 500.... A little lower than it us too.
Also if I try to drive while it is warming up it surges bad.

Changed IAT sensor, front and rear O2, TPS sensor, MAP sensor, coil packs, whole White housing under IDI cover, all vacuum hoses, and TB's. I had my ECM recalibrate and had newer program written to it by my dealer, and this helped for a few months.....did solve the problem though.

After I changed my oil/air separator it is less irate in warming up, and takes less time to idle normal than it did before I changed it.
But all hoses, gaskets, and sensors were looked over and reconnected.




PRND321 Till I DIE
Old Motor: 160whp & 152ft/lbs, 1/4 Mile 15.4 @88.2
M45 + LD9 + 4T40-E, GO GO GO

So I took it to the dealer and the ecu was reading TPS errors. I replaced the TPS and reset the ECU. It idled and drove great. Later that night I started it up and it had high idle/open loop.... I'm reseting it again and taking it back to the dealer.

ok, so ive been skimming but cant seem to find anyone that has the same problem as me.

2000 Cav z24 5 speed

-It idles at about 1400rpm, never bounces drastically(can hear it kind of rev up and down a little but not enough to show much reading on the tach). Starts idles high then comes down like normal.

-Disconnect battery and let the comp reset and then it will idle normal for a few days but then starts idling high again....

i like this problem now because my car warms up faster in the morning but come spring id like to fix it because its annoying!


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2000 Cavalier z24-5 spd, 2.4L - thinking of selling.....

Hell... my car has ideld at 1100rpm since I've had it... no problems or surges.... but it just ALWAYS idles at 1100rpm... try to fiqure that one out.... (97 LD9 btw)

Matt P

when you are going down the road, lets say coming up to an off ramp ont he interstate or highway, and you put the clutch in and shift to neutral, does the rpms stay at 1500(your normal idle) or start to shoot up, above the norm, and if it does shoot up, to what range, how high, and how long does it take to go down?

thomas

it idles down to 1400ish quickly like normal, everything runs, idles normal.... just instead of being normal and idling around 900 or whatever it idles higher up at 1400ish


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2000 Cavalier z24-5 spd, 2.4L - thinking of selling.....

weebel, check your obd 2 readings, what is the target idle speed, ur tps volt/% and map reading(volt/vacuum)
i put my money on a out of adjustment butterfly stop screw or vacuum leak



matt, have you done/checked any of the things i have listed before in the thread? eitherway, re-read it

-thomas