HIGH Idle

[jccjr1982]

Post edited to reflect current issue:

Hello everyone!

My 2001 Daewoo Lanos Automatic has been acting up.

High Idle: When I shift to Park/Neutral, my car idles really high (throughout the days it has went from 2k to 3k RPMs). When I shift to Drive or Reverse and hold the brake, it idles around 1200 RPMs. (Causing a single lurching motion)

Removed and cleaned the ISC and throttle body. Manually extended the ISC pin fully out. Disconnected/reconnected the battery. Start the car and slightly held the gas pedal to relearn the idle.

Car then drives PERFECTLY fine for a few trips, with no more high idle issue, but after a few trips the issue comes back progressively, with the idle seeming to get higher as the days passes.

This happens with all the accessories and A/C off.

Checked for leaks as suggested, and all the hoses/tubes/rubber ends appear in great condition.

I have a ScanGauge installed, no current, stored, or pending codes. If you need any other values that can be of assistance please let me know....


EDIT:

SOLVED (tentatively): Stumbling Issue: When I press the gas pedal lightly from a dead stop, it won't stumble. When I press it just a little bit harder it starts stumbling but goes away when the speed picks up. Seemed to have disappeared after removing and cleaning the ISC pin/throttle body.

SOLVED (tentatively): Irratic Idle: I shifted to Park when I got home, and the idle fluctuated up and down pretty bad, almost from kiling the engine, but it went away after a few seconds. Seemed to have disappeared with the stumbling issue.

Vehicle Information:
2001 Daewoo Lanos Automatic w/ 80k miles. Secondary vehicle that doesn't get too much mileage.
Just smogged it 1000~ miles ago, it passed with flying colors.
Replaced blown head gasket over a year ago. Also replaced the plugs, air filter, water pump, idler pulley, thermostat housing, belts during that procedure.
I constantly check the coolant and oil (due the the mental damage the blown gasket caused me), and they are at the normal level.
A/C belt has been LOUD ever since I've gotten back from Las Vegas last month. I keep spraying belt lube on it to minimize the noise. The A/C performance is great otherwise. (Ironically back during my January trip to Vegas, the belt has gotten loud and eventually snapped. Guess my A/C doesn't like the hot weather there)

[Trackerrrr]

Sounds like a vacuum leak. Check the hoses where they are attached to the intake manifold for cracks or breaks.

[Trey05Woo]

I would tell you to read my reply to the "stumble" thread. This sounds like an idle circuit problem.

[jccjr1982]

This morning on a cold start it idled even higher: around a consistent 3000 rpms.

I checked all the lines and the rubber ends, and all appear in pretty good condition (none disconnected, loose, broken, and no dry cracked rubber ends).

When I disconnect the vacuum line from the throttle body to the MAP sensor, the high idle drops to around 900-1000 RPMs, and the car seems to drive fine. (The stumbling issue seemed to disappear).

When I unplug the harness from the MAP sensor, but leave the vacuum line connected, I throw a P0107 code (which makes sense). Car still idles high though. When I disconnect the vacuum line with the harness unplugged, the engine died.

I was reading another thread on a similiar problem, and someone suggested to disconnect the battery for a few minutes. I did that, the car idled fine for a few minutes. Problem came back though as I started revving.

I'll go and read that thread Trey.

[jccjr1982]

I read your thread Trey.

How would I diagnose the ISC? I tried disconnecting the harness from the ISC valve with the engine running, and theres no effect on the vehicle. No code thrown, and still have high idle. Seems like it does absolutely nothing. That doesn't sound normal, but then again I'm far from being an expert...

[jccjr1982]

Well I removed the ISC, cleaned the pin (some soot but nothing major), then cleaned the inside of the throttle body.

Then I disconnected the battery, and then manually extended the ISC pin fully out.

Connected everything back up.

I had to slightly hold the gas pedal on first start up, but after that it idled perfectly fine for an entire day of driving, seemingly resolving all the issues I had (no more stumble and idle was pefect throughout all gears/stops/parks/etc.).

But then part of the issue came back slowly. While the stumbling seemed to have completely disappeared, the idle while I'm in Park or Netural progressively shot back up to high but steady 2k+ RPMs, and it feels like its getting higher by the day. When I shift to Reverse or Drive with the brake held, it drops to about a steady 1200 RPMs. High but at least no fluctuation/erratic behavior. This can cause a safety issue though as the car wants to lurch when shifting out of Park. Besides that I get normal cruising drivability.

I repeated everything from the beginning, and it ends up being the EXACT same scenario.

Please help!