Tom and Vipers
Enthusiast
I'm about to start diagnosing this today and my #1 suspect is a leaking injector O-ring.
Other thinking:
I've been dealing with a severe idle "hang" as high as 3500 rpm which has happened at altitudes around 8000 feet. But when extreme like this, the "hang" never drops, it just stays there. It will wander or hunt around this level sometimes with step changes in rpm which could imply a bad electrical connection. It has VEC1 and I don't think the connections were soldered - just pierced. But I don't think its the VEC1 because that would effect BOTH banks.
Yesterday, it went into "3000 rpm idle mode" from 6000' down to 4800' which is contradictory for an altitude correlation.
HOWEVER, there does appear to be a correlation with temperature: temps in the 50's may be the trigger for this mode.
EDIT UPDATE: BLOW OUT THE PLUG HOLES BEFORE REMOVING! They are FULL OF SAND here in the desert. DUH!
EDIT UPDATE 2: Checked plugs, looked good. Both banks same, no single plug showing rich.
Hot again, around 80*F, VEC @ 0/0 Low/High and the high idle crept in as soon as engine warmed up. It would creep to 3000 rpm at 4800 ft. I left it go in neutral and it would hold high for 5-10 seconds, then drop like it was going to idle with the exhaust "gurgling" BUT around 1500-2000 , the drop would abruptly stop and again creep back to 3000. This was an oscillation! I would repeat this indefinitely.
So I started adjust the VEC1 Low. I went lean and it got worse, I when something like 2 clicks rich rich and it dropped to idle and then behaved itself.
I wonder if this oscillation is the "confusion" Cragin was refering to in my high altitude thread.
RULED OUT:
The first thing I'm going to do is inspect the spark plugs and see if there is evidence of a rich injector. I shut the engine down while presenting the 3000 rpm idle.
Once I do that, I'm going to listen to the injectors while engine running to see if they are clicking as expected.
Once I do that, I'm going to listen to the injectors while engine running to see if they are clicking as expected.
Other thinking:
- Since the banks are managed independently by the ECU, a lean condition in Bank 1 could not be a cause.
- Intake vacuum leak not expected since this would cause a LEAN code.
- Sometimes when I start the car, the idle instantly spikes to maybe 2000 rpm and then instantly recovers - as if someone put a shot of starting ether - fuel puddle in intake?
I've been dealing with a severe idle "hang" as high as 3500 rpm which has happened at altitudes around 8000 feet. But when extreme like this, the "hang" never drops, it just stays there. It will wander or hunt around this level sometimes with step changes in rpm which could imply a bad electrical connection. It has VEC1 and I don't think the connections were soldered - just pierced. But I don't think its the VEC1 because that would effect BOTH banks.
Yesterday, it went into "3000 rpm idle mode" from 6000' down to 4800' which is contradictory for an altitude correlation.
HOWEVER, there does appear to be a correlation with temperature: temps in the 50's may be the trigger for this mode.
EDIT UPDATE: BLOW OUT THE PLUG HOLES BEFORE REMOVING! They are FULL OF SAND here in the desert. DUH!
EDIT UPDATE 2: Checked plugs, looked good. Both banks same, no single plug showing rich.
Hot again, around 80*F, VEC @ 0/0 Low/High and the high idle crept in as soon as engine warmed up. It would creep to 3000 rpm at 4800 ft. I left it go in neutral and it would hold high for 5-10 seconds, then drop like it was going to idle with the exhaust "gurgling" BUT around 1500-2000 , the drop would abruptly stop and again creep back to 3000. This was an oscillation! I would repeat this indefinitely.
So I started adjust the VEC1 Low. I went lean and it got worse, I when something like 2 clicks rich rich and it dropped to idle and then behaved itself.
I wonder if this oscillation is the "confusion" Cragin was refering to in my high altitude thread.
RULED OUT:
- Injector o-ring leak (no single plug presented rich - of course, if one injector started dumping fuel, how rich would the other cylinders present in that bank? I don't know.)
- Intake vacuum leak (how do you make a bank go rich with a vacuum leak on that bank?)
- DRB the codes and look at the plot O2 and fuel trims.
- The heart of Speed Density may be the MAP sensor. Clearly the VEC1 has a dramatic effect on idle. Of course on my car, this behavior may be a symptom of something else - I don't know if anyone changed my ECM programming.
Last edited:
