Back Again: Won't Idle

[Augster]

Well, I'm back again, but for a different issue:

After getting the car running perfectly, smooth idle and all with proper adjustment of the throttle plates and IACV (screw), I took it to get smogged, about 15 miles away through mostly city streets. Had zero problems and the car ran perfectly with full AC. Smog shop ran the car for about 15-20 minutes, but had problems with their machine and asked to come back another day when they get their second machine fixed and running. So I decided to take the car onto the freeway for a little joyride, but after about 10 miles the check engine light came on. When I got back onto city streets, the car would eventually die while idling; I had to always keep the RPMs up via throttle.

Returning home I pulled the ECU codes: 21 Ignition Circuit, 34 Detonation Sensor Circuit, 35 EGR Temp Sensor Circuit, and 42 Fuel Temp Sensor Circuit, however, I have never pulled and cleared codes before so these could all be residual codes. I cleared then started car. Again, the engine would eventually die during idle, but no check engine light manifested itself. And the idle quality wasn't significantly bad; it would seem to run fine for a few moments, but then the RPMs would suddenly drop to approximately 500 and start to get rough and sputter.

I checked for misfire by pulling each coil wire and each resulted in detectable misfire and rough-er engine idle, so it doesn't appear to be ignition related. It would also appear that there is sufficient fuel getting to every cylinder because again, there was always a misfire with a coil wire pulled, but returned to smooth-er running when reconnected.

Adjusting the IACV screw to get higher idle RPMs didn't do anything, unlike before when I got the car running perfectly, the idle was sensitive to IACV adjustments.

There is a hint of fuel vapors around the passenger side, but I could not visibly detect any fuel leaks on either side, on fuel lines, injectors, fuel rails, or on top of lower plenum.

I rechecked ECU codes and there was no malfunction detected ("55").

I'm now at my wits end here, even possibly believing that it could be the five year old fuel where after driving it approximately 20 miles it started picking up some of the "bad" stuff (there's still just under half-tank left). And this is a completely different idle issue than 5 years back, when the car was mis-firing on multiple cylinders, whereas now it doesn't appear to be a mis-fire issue; perhaps an issue of fuel quality or quantity.

Is it time to enlist a "professional" shop to take over diagnostic?

Or were my initial corrosion issues discovered in my wiring connections really a microcosm of the larger issue of a 24 year old brittle and corroded EFI wiring harness that really needs to be replaced to resolve all these maddening issues?

Another possibility is that I used butt-splice connectors for the injector pigtails, however, they were designed for only as small as 18 gauge. One wire of each injector appears to be 20 gauge so I'm wondering if a butt-splice worked itself loose during the drive (even after heavy taping) and is causing intermittent injector(s) operation.

[Augster]

Upon further research, I no longer think it has to do with faulty injector wiring because that should have triggered an error code 51 FUEL INJECTOR CIRCUIT, which would most likely be an "open" (i.e. broken/disconnected/intermittent) circuit since a "closed" (short) circuit would supposedly damage the ECU. But there was no code 51 recorded by my ECU, either before or after resetting.

I really wasn't looking forward to pulling the fuel injector connectors, specifically #1, because I had to grind a portion of the upper plenum (the forward protruding "leg" that's one of the mounting flanges for the throttle rod linkage) but I didn't grind enough to allow the connector to be pulled off the injector.

[NolimitZ32]

Have you tried to listen to the injector to see if it's clicking? running on 5 cylinders wont make your car die, it will idle like crap but it will stay on.

[Augster]

Haven't listened; too much noise everywhere so will have to figure out how to filter how everything else and concentrate on each injector individually.

But have to wait until tomorrow as I'm heading out of town now.

[NolimitZ32]

long screwdriver, put the tip onto the top of the injector and the end of the handle to your ear, you should be able to hear a harmonic click.

[Augster]

As far as I can tell with the screwdriver to ear method, all injectors are functioning with a rhythmic "ticking" at a constant frequency. I ensured I was listening to the actual injectors by touching the screwdriver to a different location farther away from the injectors and didn't hear any ticking. And I went around all injectors three times just to make sure I was listening for the right sound.

I ordred a bottle of Iso-Heet to treat the 5 year old gasoline in case water has condensed within it and is now being drawn into the fuel system. Will arrive tomorrow and will wait after that (will probably drive around to empty the 3/8th fuel remaining then fill it with fresh premium) before performing other tests, though I'm not sure what else to test if it's not bad fuel. It could be a vacuum leak, but without knowing what the vacuum reading should read at idle, not sure if I could properly detect any slight vacuum leaks.

[NolimitZ32]

If you are afraid of water in the fuel I would strongly suggest you open up the tank and suck all the fuel out, also take the opportunity to make sure you have no particulate settlement in the bottom.

[Augster]

I've been sidetracked with other projects, including the upcoming turbo replacements of my BMW 335i.

Anyways, what I'm really concerned about is if the idling is not electrical-related nor fuel-quality related.

Because I'm about to pull the engine to replace its turbos, and with the engine out, replace the EFI wiring harness entirely along with all vacuum lines. If after all that, it still idles like crap after fresh new fuel, then I'm all out of ideas and will be forced to enlist the help of a "professional," which can run into the hundreds of dollars.

I've already replaced all PCV valves, all injectors, fuel filter, checked the operation of the all the components comprising the IACV and PTU. And by eventually installing a brand new wiring harness and vacuum lines, I think I would have covered all possible causes of idle quality issues. The only thing I would not have touched are the fuel pressure regulator and damper above the plenum.