Smooth idle but take a few secs to find it!

I thought that was normal (mine has done this consistently for years and years) but if you happen to find some magic potion (Techron?) then let us know and I will try it.

 

Have not noticed mine doing something like that.
Jes

 

Could be vacuum leaks around the intake manifold. The old gasket design was not too good and has been updated, at least on the V12s. I have my intake manifolds torqued every annual because they tend to vibrate the nuts loose. Torque value is very low, so that adds to the problem. At my 5 year last month, the old intake manifold gaskets were completely shot and deteriorating. Small bits of the gaskets were undoubtedly being ingested.

 

Mine comes back to an immediate smooth idle. Maybe we can do some video to compare?

 

I recommend using a graphing OBD2 reader and look at:

MAF A
MAF B

TPS

O2 A
O2 B

Then look for abnormalities in the data like oscillations in MAF or O2, that might cause a surge at idle.

Graphing OBD2 readers are <$200 and a great tool to use when you have troubles or want to look smart in front of the opposite sex.

 

I get more of a "wtf are you doing now???"

 

Sounds like you didn't wait for the "Check Ok" to illuminate before crabking...? BTW, if it doesn't hit normal idle almost immediately then you may be better off turning it off and restart.

BTW, OP is not referring to idle at start-up, but idle in general coming off the gas.

Jes

 

I have a 2004 manual with 24k miles on it. In have driven all but 8k of those miles. On Memorial day this year my car began to do the exact same thing. Richard and Fernando at Competitzione have gone through the car very thoroughly. We tested alternate throttles, MAFs, smoke tested, re-flashed ECU with 3 different programs, tried 100 octane gas, changed the intake gaskets (which were fine BTW), had the fuel injectors sent out for recalibration (2 were dripping), checked torque on intake runners. And that's not an exhaustive list...just what I remember. None of this cured the problem. And to clarify...I always let CHECK OK appear before ignition.

At this point I'm just living with it until the next major where we can verify timing etc...although it would be very unusual if it were timing given that it hasn't thrown any CELs at all. I also notice some sporadic hesitation in second gear acceleration. What I'm about to suggest comes from a point of ignorance and only using my deductive reasoning that has served me well as a computer guy...could it be something to do with the accelerator pedal position sensor? Where the sensor is sending the wrong values to the computer and therefore it is trying to compensate for that? Maybe that's ridiculous. Its's just something that occurred to me the other day.

 

I'm happy to grab an obd2 data set from a car that doesn't do it... And then compare it to one from a car that does do it...

 

Have same problem, no vacuum leaks, new sparks, coils, Mafs and O2 didn't fix.

 

The TPS is differential. It has two potentiometers, one going from 0-10k and one from 10k-0. the ECU makes sure that both signals match, where match means they are opposite. A grounding issue, floating ground, or 5v high level could offset this and cause issues, sure. A meter or OScope can check this easily.

 

Wow...well let's not get excited yet...but why don't you go back in to the pedal connector and reclean/refit the connector to see if it makes a difference. I need to get a bit of contact cleaner to try this.

 

The problem is at initial cold start, where your motronic units aren't even looking at oxygen sensors, so looking at what they are doing/not doing is pointless. They are open loop. It's more likely a MAF issue, you won't get a stored error unless it totally fails. You need to look at the long term fuel trims or put an oscilloscope on the MAF's and measure the signal voltage coming out each of them at idle.
If it was inlet manifold gaskets you would have a MIL.
If the MAF's are ok you might have a CAN issue, sometimes one side of the engine "wakes up" before the other because the CAN line doesn't initiate properly at start up. If it fires and runs rough but you switch off and re start and it's ok then this could be the cause. It's Often system voltage related.

 

Tubi exhaust and valves open: my "idle" does not do what you describe coming off the gas.
Jes

 

The problem in my case is not at initial cold start. In fact, the car idles smoothly (for cold start) until it gets out of the cold start program and drops the revs down. My issue happens at operating temperature when coming to a stop. The revs bounce around 1000-600 and then finally settle at the normal 1100-1200 idle. We did notice a lean condition on the 5 and 8 cylinders (IIRC). However that correlated with the dripping injectors as well. I haven't been back to the shop to get codes read. Perhaps it has set new ones w/o a CEL.

MAFs were switched out on both sides with known working units from a 360 challenge car. Nothing changed.

For completeness - my car has Tubi headers, hyperflow Cats, and Nouvalari Exhaust. No valves at all.

 

I have a 2000 360 with OEM headers, hyperflow cats, tubi exhaust. Over the past ~4 years I've owned the car I've done the intake clean/gasket and new cats due to a CEL...maintence on the grounds and spark pluts, and the car has been properly serviced every year including re-torquing of bolts. Both MAF's were changed when I was having the CEL. Car runs great!

With that history, I occasionaly notice a slight variation when coasting to a stop- one time it's been consistent through the 4 years is coming up my road which is a steep hill and curve- I come up in 2nd gear going maybe 20-25mph and turn into my driveway, and put the car into neutral as the car coasts down my driveway. I think just about every time in that scenario it fluctuates down to maybe 800 or 600 rpm about 2 times and settles at 1,100. The idle fluctuation I'm describing sounds like yours, and has never bothered me. The car performs great- I bring up my history to say through all of the work (almost all of which was related to fixing the CEL once and for all) the idle thing stayed- I just assume it's normal operating for many of these cars under certain conditions- in my case maybe the very light throttle for 1/10 of a mile going up my hill then coasting down my driveway sets up a situation where it would do that.

Like I said, it doesn't bother me and I wouldn't spend a dime on trying to fix it...I'd mention it to my mechanic if I thought it was related to some other issue, but the "idle search" itself doesn't concern me.

 

Has anyone ever taken one of the MAF's apart to see if they can be cleaned or otherwise checked? I am imagining some sort of flap inside.
It seems to me if you did a physical check of the MAF's and cleaned or checked the electrical connection to them that you could scratch them off your list.
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Did you try this stuff?
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