2000 Bonneville, erratic idle, tried several things but lost

[bschoole]

2000 Bonneville SLE 3.8

Got it for cheap, needed lower intake gaskets, had them replaced by a friend but not sure if he caused the problem or what

Idles fine when first started, when engine is cold, idles at about 1200-1300 rpms, as soon as it warms up, and drops the idle to below a 1000, its get a chugging noise.

The rpm's don't appear to be moving, but you can hear the engine sort of pulsating, you can also feel it if you are in drive at a stoplight, rpm's drop to about 600 and stay steady, but you can feel and hear the unevenness of the engine.

Replaced both the tps and idle air control valve, also replaced pcv recently. The car has stalled a couple of times, although both times were when cold and it seemed to be idling fine and then just quit.

Wondering if there is a sensor i am missing, or if perhaps i have a vacuum leak that could be causing it. Just trying to get my bearings before i start tearing apart stuff.

Oh and also, don't know if related or not, seems to loose some power after it gets warm, pretty noticable actually. Shifts fine and seems to rev up fine, just seems much slower after getting warm.

Thanks for any replies anybody!

[Airjer_]

Sounds like a possible MAF sensor flaking out. They have been really common as of late. Sometimes you can wiggle the connector and get them to act up or get the symptom to clear up.

[truc0011]

Originally Posted by Airjer_

Sounds like a possible MAF sensor flaking out. They have been really common as of late. Sometimes you can wiggle the connector and get them to act up or get the symptom to clear up.

I agree with Airjer, I just had the same issue and it was the MAF.

[Jrs3800]

Is the SES light on at all?

More than most if the MAF starts to flake out on these it will trip the SES light with a set MAF code.. If there are no codes unplug the MAF and see if the engine idles any different...

When you replaced the PCV valve, did it have an O ring around it?

[bschoole]

thanks for the replies, i ended up replacing the MAF, which cleared up some hesitation problems. However the Idle problem is still there.

When the engine first starts and is cold, its idles at about 1200-1300 rpms and sounds fine. When it warms up it idles at about 700-900, and puslates, the rpms don't move but you can hear it and feel it. Also going from gear to neutral or park, it almost stalls, the rpms drop and it almost dies and then shoots up, it will settle at 700 and then slowly creep its way up to a 900-1000, and then might drop down, and then increase again. Its almost like it constantly having to correct the fuel-air mixture, but can't do it quick enough.

The pcv valve did have an o-ring btw. I am still at a loss. On a side note, the engine has a whine on the belt drive somewhere, not sure if its part of the problem, but drives me crazy

[bschoole]

I think i found the problem. I had someone replace my intake gaskets on my car, and it looks like in there rush they sheared one of the bolts off the intake manifold plenum that the throttle body attaches too. This has left the throttle body with a fairly significant vacuum leak. So looks like i am going to be replacing my upper intake manifold. Oh joy

[HotZ28]

What has the person who changed the UIM, had to say about this? Surely, they should offer a solution?

[bschoole]

Well it was my cousin who did, and while i did pay him, It will be too much trouble to ask him to do something about it. I wish he woulda been man enough to tell me he did it though, cause I have been trying to fix this problem forever.

Oh well, I found the whole plenum and gaskets for $60, I have done it before, its not terrible difficult.