It sounds like it could also be a small vacuum leak at the intake manifold gasket. Maybe at idle you've got enough vacuum to pull air in through the gasket till some gas is applied, vacuum lowers and it stops pulling air in through the gasket area.

Mikey

 

We looked at the car again this morning. Here's information from one of my earlier posts:

O2's stay below 500 at idle. Speeding the engine up makes the O2s switch from 800-900ish to 200ish and in between. While the O2's read lean at idle, the fuel trims eventually max out. Engine runs a little rough at idle but there are no misfiring cylinders. Sounds more like a big cam than anything.

Speeding the engine up say to 2500 RPMs just sitting still makes the O2s start to switch from high to low like a normal O2. When that occurs, the fuel trims come down to normal level.

At idle the IAC counts go to 0 even though it's still running (albeit rough).

Here's some more things we did:

Checked and pulled every hose and capped the vacuum port and hose with no change.
One hose was questionable so we changed it with no change.
Sprayed EVERYTHING with a good thick fluid with no change.
Snorkel from TB to MAF was in perfect shape.

This is important:
When he puts the automatic in gear and holds the break on but no throttle, the idle comes down about a 100-150 rpms lower. The IAC numbers start rising 28 to 30 and O2s start swinging like normal. The first hose we checked was the vacuum line going to the break booster. This lead me to believe the only problem was the throttle plates are open too far since once the idle comes down, it seems to be ok.

I noted the following:
Idle is about 1100. Requested idle is 800.
Vacuum at idle is about 13 in. Hg. Rev'd to about 2000 and vacuum goes to 20 in. Hg.

It appears the idle stop screw has been nearly maxed out. Perhaps because of the lopy idle.

I told him to back off the throttle stop so that presumably the IAC will take over.

I wouldn't think the O2 readings would lean out and then the fuel trims would max out because of the throttle stop being set out too far. The IAC readings yes but not O2s. Seems it has to have air coming in that's unmetered from somewhere.

I didn't think to test the MAF.

What am I /we missing?????? Don't think just the throttle blades being open too far would cause the O2 readings.

 

Big cams have large overlap. Large overlap causes the outgoing exhaust to pull some of the incoming fresh air charge out with it = seemingly lean exhaust. Hard to tell how big the cam is, but his signature description would lead one to believe its on the large side.

Also might want to check the location of the O2 sensors. They may not be getting hot enough at idle to put out the correct signal.

Also check for a leak somewhere between the MAF sensor and the throttle body.

 

i have the cc306

as for the o2s location i have jet hot long tube

 

messed around with the IAC today and this is the results

*initial setup
tps .52
l159/r160 block learns
l128-130/r139-141 integraters
rpm 1000
iac 0

.54
160/141
125-127/132-134
1150
iac 0


when I adjust the throttle blades more shut iac counts went up but fuel trims still sucked......any thoughts

 

Doesn't this still point to some issue with the brake booster line? Was the line disconnected and know for sure that it was totally capped off?

Edit....just reading again...so the idle does not drop when just applying the brake....so the tranny is putting a little load on the engine when putting it in gear...this seems normal for the idle to drop. Hmmm, sounds like a nice little problem. Does still make me wonder about the vacuum leak.

 

Any Exhaust leaks?

 

bump

 

Have you fixed this problem yet? I am anxious to hear the fix.

 

nope. really dont know where to go from here.