erratic engine idle

[ssd]

got a e53 petrol 3.0 that has engine check light on and erratic engine idle.

(Peake code reader gave faults as Table 19: CA -O2 sensor control limit cyl 1 -3 and C6 catalytic converter efficiency cyl 1 - 3 plus some misfire ones).

My question; Is this indicating an air leak after the maf or something related to the O2 sensors?

ideas appreciated

[Weasel]

The misfire faults are of course misfires, which may need to be diagnosed on their own. (easy if it is a constant miss)

The cat converter efficiency fault is telling you the cat converter isn't cleaning the exhaust as good as it should be, but usually just clearing it will get rid of that fault for a few years... At least in most cases.

The o2 sensor control limit is a mixture fault. The other info needed to diagnose that is whether it is a rich mixture fault, lean mixture fault, adaptive or multiplicative fault. (adaptive = at idle, multiplicative = under load)

[ssd]

thanks Weasel, you got me wondering so I've checked the codes again and got table 19 CA, C6 (as before) but also

E3 - O2 sensor adaptation limit cyl #1 - 3 and,
E4 - O2 sensor adaptation limit cyl #4 - 6

does this help and if so what does this suggest? no misfire codes btw.

[Weasel]

Well, I just said misfires from reading the first post.

What that tells me is whatever is causing a mixture fault is affecting both banks... but not whether it is lean or rich, idle or under load... The more common would be lean and at idle, and one of the more common problems for that would be the smaller elbow offshoot of the rubber air duct torn in the ribs. Check where the air duct goes from the MAF sensor to the engine, the smaller elbow that goes to the idle control valve makes a bending turn, on the outside edge of that turn is where it cracks between the ribs.

[ssd]

I agree you didnt say anything about the misfires - i did in my first post Reason being it did have misfires on all cylinders before i cleared them along with the o2 codes.

ok - how do i go about finding if the mixture fault is lean or rich, idle or under load?

I'll check the elbow I know exactly which one you mean because when i changed the ccv (oil sep) recently i had to remove all the air intake tubing and throttle body (not the intake manifold method though) - could it be that i done something on refit like not seated the gaskets? I was a little unsure which way the rubber gasket faced near to the maf because it did not have an obvious channel for the ribs to sit in.

[Weasel]

To get more info on the faults would require a different/better code reader that actually gives fault description vs just a code. I have this one at home:

Equus Products, INC.

But you can get by with the 3100 for just fault code description and the 3130 has live data feed to look at the sensor readings etc.

[ssd]

thanks - just bought the peake code; could maybe look at getting a obd2 one then

question - do the gaskets in the air duct have a particular way in which they are fittted?

[Weasel]

Kinda yeah, but if all the hose clamps are tight and no air is getting in you likely have it right.

[ssd]

Right no luck so far...

changed rubber throttle body boot, gasket and cleaned throttle body

Replaced all gaskets in air duct and hose clips

Codes came up as before and check engine light on

What now - i'm out of ideas? (calling for Weasel's help)

[Weasel]

You still don't know what mixture faults you have yet... so continuing to throw parts at it in hopes of finding the right part is kinda a waste. If it is rich mixture under load it could be the MAF sensor, lean mixture at idle could be a vacuum leak from anywhere including the crankcase vent valve/oil separator.

Point is you don't yet have the details on the problem needed to even guess right, and don't have the proper tools to diagnose further like reading adaptive and multiplicative values, read the MAF values at idle, watch the o2 sensor readings, smoke test the intake system etc. That is why it is sometimes cheaper to just pay for the proper diagnosis vs pay twice as much in unneeded parts before finding the rear problem.