Idle issues 99 Lumina

[JP]

I'm on the final few months and want to keep this baby going....maby 10K more miles.

Got a few codes to deal with:

P0440 EVAP Not worried about this one

P0113 IAT Sensor circuit High voltage

P0102 MAF Sensor circuit low frequency


I was having problems with a wavering idle and occasional stall. Figured it might be the IAC valve, so I just replaced it; the old one was carboned up pretty well. That seemed to improve the wavering adle a little bit, but now when I start it, it sounds like the air intake is off the throttle body...you know, that whooshig-sucking sound for about a minute and the idle doesn't know what to do...it wavers all over the place between about 600 and 1200 rpm. After a minute or so, it settles down to a fairly even idle.

I haven't taken off the air intake to see if anything is obstructing or if the flange has come loose (yeah, I know...that's the first thing to check...but I will tomorrow.

I erased the codes and got an immediate P102 set; no P113 or P0440 yet.

Anything come to mind? Seems to me that the 102 and 113 are related....

 

[billr]

How many things did you disturb changing the IAC valve, just the screws holding it to the throttle-body? When you put the new one in, was the pintle retracted all the way, so it wouldn't get mashed into the seat in the TB? Obviously, check the electric connectors to the IAT and MAF sensors, they must be real close to that area, even if you didn't mean to disturb them...

 

[JP]

Yep, I measured the extended length of the pintle on the new one to make sure it was where it was supposed to be and only messed with the screws for the IAC solonoid.

I'll check the connections to the IAT and MAF sensors next. It seem logical that it's one of those sensors or the connections acting up.

 

[dabunk]

Did you clean the throttle body and throttle plates first? Carbon buildup will screw with the idle alot.

 

[Gus]

3.8 or 3.1?

Does the vehicle idle better with the MAF disconnected?

Have you checked for vac leaks?

Also a bad O2 sensor can conflict with MAF readings....

 

[kev2]

I agree with Gus - Vacuum leaks.. Maybe the MAF and IAT are being ' bypassed' with unmetered air
DO you have a scanner?

why are you ignoring P0440?
A vac leak in the EVAP would skew the MAF see below...

From trouble tree P0102-

Any un-metered air may cause this DTC to set. Inspect for the following:
An engine vacuum leak
The PCV system for vacuum leaks
An incorrect PCV valve
The engine oil dip stick not fully seated
The engine oil fill cap loose or missing

 

[JP]

The P0440 code has been present for two plus years without any issues.

Here's another clue; when the engine is warm, it's not as bad at idle as when the engine is warming up.

Wires seem well connected to all sensors.

 

[JP]

Replaced the IAT sensor, thought what the heck. No significant change, although it will idle fine after it settles down. Rev the engine, and it has trouble settling in at a consistant idle, but after a couple minutes, it will idle steady for 30 or more minutes (yep, I let it idle that long to see if it would act up).

 

[Gmolds66]

I had a very similar problem with my 94 Lumina Euro. It was 3.1L that developed an idle problem. Long story short... I needed to do an idle learn procedure to get it running right.

It's recommended to do this procedure whenever you change an electrical component or when the car looses all electrical power. The procedure can be done two ways. The first is with a GM Tech I scanner. The second is done manually.

To do it manually, first disconnect the positive cable from the battery or remove the ECM fuse under the hood for at least thirty seconds. Reconnect the battery or insert the fuse. Chock the wheels and set the parking break.

Start the vehicle and put it in drive leaving all electrical accessories turned off. Don't even turn the steering wheel during this entire process. As the car tries to figure out where it should be idling, give it fuel if needed to keep it running. It will eventually idle on its own. Let the car run until the cooling fan comes on. (about 10min.)

Turn the vehicle off at that point while still in gear. Wait 10 seconds and restart the car and immediately put it in gear again following the above all off / no wheel turn procedure. Let it run like that for 5 min.

Turn the car of again. Your next restart should give you normal operating results.

 

[JP]

I had to replace the battery, and now it idles fine at rest unless I goose the throttle, then it goes wacky. When it's warm...no problemo, no "wacky" idle.

I guess that I'll just leave it; we'll either sell, trade or junk it before the weather gets cold here.

 

[JP]

Changed my mind; I decided to fix the rough idle on my 99 Lumina before selling it, as it will be difficult to explain away a rough idle as a minor problem. So, before I begin working through the P0102 and P0113 codes, a question came to mind:

Could it be as simple as a bad PCV valve? I know, lots of other stuff could be wrong; corroded or loose wires, bad sensors, etc, but it occured to me it's been a very long time since I serviced the PCV valve.

Cheap and easy would be very cool. Is it possible that this could be a miracle cure? Murphy's Law says that it isn't very likely, I know.

 

[billr]

Sure it's possible the PCV valve is giving you a bad idle; if it isn't operating correctly it can become a "vacuum leak" with the same effects as any other. Easy to test for that, pull it out of the valve cover or wherever it is, often just pushes into a rubber grommet, and put your finger over it to plug it and prevent air-flow. If the idle improves like that, then the PCV is probably passing more air than intended.

 

[JP]

OK I found the problem! The MAF sensor is not putting out a signal. Checked both the positive and negative terminals, and they are fine. My Enginuity scanner shows intermittant function....I thought it was the connector, so I replaced that, but it's still intermittant.


Can a MAF sensor work intermittantly?

Where can I get a working used one? I'm selling the car, and don't want to shell out a hundred bux or so for a new one, but I don't want to sell the car when some kid might have it stall at the wrong time. Any recommendations for used part suppliers?

 

[JackC]

Wrecking yard. Pick N Pull type yard. About 1/2 the price of regular yards. 1/4 the price of new. You take it off yourself. They sometimes will guarantee the part, only meaning you can come back and get another used one if the first does not work.

Find a vehicle that is badly wrecked, but appears to have been well maintained. . It PROBABLY ran fine until the accident and therefore has a good MAF.

 

[JP]

Sigh. This car hates me.

Replaced the MAF sensor (got one cheap online) and it took care of the idle problem....but.....

When I started it, it stalled immediately...but would stay running if I kept the RPM above idle speed...then after a minute or so, it would run fine.

Restarted it again, same thing.

WTH? I erased all codes (MAF sensor low voltage and O2 sensor codes), and not codes have reset.

It was low on gas, so I added enough to get up to a quarter tank.

I plan on cold starting it tomorrow am and see what happens. Any ideas?