FBIII

I would think the fast idle is key to the diagnosis. Are there any other conditions other than a vacuum leak that would cause a fast idle?

Tom in Austin

Hey Rob, I'm right there with you man ... my car developed a high idle right after I threw some Techron in the gas tank and hasn't gone away after another tank of gas.

Idles now 1,300 - 1,400 rpm in park, 900 or so in drive. Same as you, ok when cold, then goes up with warmup. ISV keeps trying to pull it down, cycles back and forth when coasting with closed throttle. Runs perfectly other than the idle.

Plan to whip out the M-Vac this weekend and start checking all the vac lines. Sean replaced my Temp 2 connector back in July, O2's been in there since 2008, MAF rebuilt in 2010 ...

IcemanG17

high idle typically speaks of vac leak.....maybe even an odd vac leak at the idle regulator....Sharky had a constant LOW idle....as soon as I fixed the regulator it was rock solid perfect....

On vac leaks.....have the new owner try the brake cleaner test....once car is warm spray brake cleaner around sealed parts and around the intake.....if the cleaner hits a certain area and the RPM goes UP...bingo you have a winner for a leak....when we changed engines in my lemons racer the intake runners had slightly warped to the old head....a quick "square" shaving up the intake runners solved this problem...never heard of this with a S4 intake...but who knows....

Not sure how an intake leak would cause an insane rise in C02....my initial is there is a problem with the gas analyzer at the smog shop...since I have NEVER-EVER heard of smog numbers like that....even ones that run like crap

Bill Ball

What is the vacuum reading at idle? MitiVac plugged into one of the manifold vacuum sources is how I check this. Should pick up an indication of even small vacuum leaks (i.e, one small connector open drops vacuum about an inch). High idle is hard to account for with anything else, unless somebody disassembled the throttle and moved the idle stop screw (you'd still see 90 MPG off throttle if the idle switch is working despite the throttle plate not seating).

I'd go to another smog facility for a retest. Those numbers make no sense unless something major happened to the car. Sure, it could be rich due to a Temp II open circuit, but then the car would be hard to start when warm. If it runs OK, I'd be suspecting the smog test, although the screwy high idle is a sign something is way wrong along the lines of a vacuum leak. Was the car idling like that when you sold it?

GregBBRD

Any vacuum leak will lower the CO, not raise it.....unless one of the interconnecting hoses to the regulator or damper fell off.

Check that.

Go get it hot and retest. My guess would be that the O2 sensor wasn't hot enough to respond....or the cat was stone cold.

ptuomov

That's a good theory. If the FPR or the vacuum line to the FPR is leaking, then two things will happen at idle. First, the FPR does not see the vacuum in the intake and doesn't know to lower the fuel pressure 1:1 with the manifold vacuum. This will cause the car to run rich. Second, the vacuum line leak itself will feed more oxygen to the intake manifold, causing the idle speed to increase. However, the air leak into the manifold is not large enough to fully offset the rich condition caused by the faulty FPR or FPR vacuum line. So it's still running rich. If this is the problem, it should run richer than usual with vacuum in the manifold but run about normal at WOT.

Rob Edwards

The next owner checked vacuum at both dampers and the FPR, all three held vacuum.

After I reinstalled the engine in the GT in 2010, I took a video of the car at idle. About 17 mm Hg:




To thicken the plot, he also checked the plug wires to make sure they ohm properly. (Back in 2010 I swapped the younger wires from the GTS onto the GT engine), the distributor end of wire #4 looks like so (and has a resistance that jumps all over the place:




So perhaps that wire finally went TU- I'd guess a _really_ poorly firing cylinder might create a lot of CO and borderline high HC....

Will also advise the NO to cook the cats before the next smog attempt.

jcorenman

Throttle-plate stop mis-adjusted by a PO (or PPO) to fix a slow-idle condition.

That doesn't explain the high CO, but the CO problem is new and the high-idle is an old problem-- so I don't think they are related.

High HC and very high CO... I am liking the ignition wires or terminals, a misfire looks lean to the O2-sensor which then adds more fuel. Interesting problem...

Rob Edwards

My spare #4 spark plug wire measures a steady 3890 ohms, it's in a box headed to VA.

Fingers crossed that that is the issue!

Mrmerlin

I had idle issues with a GT engine a new ICV cured things go to about post 38

https://rennlist.com/forums/928-foru...-the-idle.html

Rob Edwards

Update: Sent the NO a different #4 plug wire, he got the cats good and hot, and re-tested, at the same smog station.

HC cut in half, though still twice what it was the last time I smogged it in 2012.

Idle CO dropped 6-fold, but still fails with high CO at 2500 rpm. and still 6-20x greater than June 2012.

Hot idle is still high, 938 vs 1013 last week.

First test vs. Second test:



He also ohm'd the Temp II sensor at ambient this morning, it was ~1900 ohms on each leg to ground. So the <5K mile Temp II is in spec.

So if one ignition wire is gamey, probably stands to reason others might be suboptimal..... Passenger side coil wire replaced in 2009, but not the driver's side. Coils are original, AFAIK (no receipt for ever having replaced them...)

Before the NO came and picked up the car, I took it out and bedded in the pads and rotors, and generally hooned around it in, might have hit redline once or twice , the car ran like it always did. Which is to say, fine, excepting the too-high warm idle, which had always been an issue over the course of my ownership despite two separate intake R&R's to ID possible leaks.

ptuomov

Rob -- I think you know everything already that Rennlist can offer. I am just speculating in what follows. If there's a way to find out how much free oxygen there is after the cat, then I think you might be able to nail it. You have excess hydrocarbons left over, and a lot carbon monoxide. Both burn. If you in addition have free oxygen in the exhaust, then it must be incomplete combustion, which in this case points to the ignition system.

JWise

Change the spark plug on #4? Or maybe all of them and retry?

Lizard928

based on those numbers you are seeing, your ignition system has other problem.

You have probably 1 cylinder that isn't firing part of the time.

Tell him to unplug each fuel injector 1 at a time and ensure that every one has an effect. I will almost put money on the fact that one or two dont based on those numbers.
Once that is fixed the numbers will come right down.

Rob Edwards

Tuomo, please allow me to respectfully disagree.....

Colin, if unplugging one injector doesn't change the engine's note, that doesn't differentiate an injector plug fault vs. a dead injector, correct? I thought all the injectors were wired in parallel, so that one broken wire immobilized the car (?)

Injectors are original but got the Witchhunter spitshine a couple of years back.