I started a thread awhile back regarding an idle issue that popped up out of nowhere after installing a new ACD pump. I've ruled out the pump as causing the issue, but I still haven't been able to figure it out. Here is a quick descrition of what it's doing. At idle, it sounds like a Subaru, a cylinder is definitely not firing properly. Under any sort of load, the stumble goes away. No misses under boost either. Rev the engine up, it mostly goes away. Only when settling to idle does it come back. As I said before this issue popped up out of nowhere. I had the car idling in the garage after installing the pump, and it was fine, then out of nowhere it almost dies, and then comes back to life with this Subaru idle. All in about a span of 5 minutes. It's been that way since.

Things I have checked:
-Compression was checked last year, it was good, I don't think it's that.
-Changed the plugs (after changing and idling for a while, I pulled them again - cylinder number 3 (from left to right) looks like it's running very rich compared to the others. Dark and sooty, but not oily or wet in any way. The car has not been driven on the new plugs, just idled.)
-Checked plug wire resistance, verified spark - good
-Checked injector resistance - good
-Checked all wiring to ignition and injectors - good
-Because of results with new plugs, pulled the 3rd injector to see if it's dirty - it looks clean.
-Checked MAP sensor and AIT sensor-good
-Checked IAC resistance in the motor and verified it was moving - good
-Checked for vacuum leaks-none found
-Checked timing-spot on


All things are pointing to cylinder #3 obviously. I'm stumped though because if the injector was stuck on, that plug would be wet, and it's not. Or if I wasn't getting spark, it would be the same, no? I don't know what to do at this point. I've also tried resetting the AEM and loading a different map, no change. Could it be an issue with the ECU? Sorry for the wordy post, I'm at about wits end with this effing thing.

I have a video of anyone thinks it would help. I'll post it tonight. Mods are in sig. Thanks in advance for any help!

 

You could eliminate the injector by swapping it with one from another cylinder and seeing if the problem moved with it. Likewise plugs, coilpacks, leads, etc, basically anything it's possible to swap, do that as it's free. I would also, at this stage, be looking to try another ecu.

 

just a basic power balance test should suffice

 

Thanks for the suggestions. What do you mean by power balance? I'll try swapping the injectors tonight.

 

Ok, after some other issues that have been taken care of, I'm still having this misfire at idle. Here is what is going on. At idle only, the car is running on 2 cylinders. You can completely unplug a coil, and the car will run the same, which makes you think the coil is not sparking, right? So it's a bad coil you say? No, because if you plug the coil back in (which makes no difference in how it runs), and then pull the plug wire, it's definitely sparking. You can hear it arcing and popping. But wait, there's more! This issue switches from coil to coil. Sometimes it's the coil on #4, then other times it's coil #2! If you give the car any gas or put it under any load, the miss goes away. It makes power and runs good everywhere else. The car has been to the tuner and he is stumped as well. Just so no one asks, the plugs are brand new, and we switched out coils. No difference. Compression is also good, as is leak down. No valves are bad/bent, all lifters are good. All things are pointing to the ECU at this point. But it still doesn't make sense why it would happen at idle ONLY. Thoughts?

Check out the vid:

http://www.youtube.com/watch?v=CUFj2vZVftQ

 

Bump for the night crew.

 

Agree it's pointing to the ecu, have you done any checks on the fuelling also? What I mean by that is, is it possible there could be an issue with the pump, or the wiring from it. Sounds unlikely, but at this stage, worth a look.

If this has only been happening since the ACD pump change, it sounds like too much of a coincidence for this to be unrelated....think about what was touched during the swap, was anything else disturbed in order to work on the pump? That said, don't rule out anything, however unlikely, trust me, I've had several months of nonsense this year looking for problems that weren't difficult to solve, just to diagnose.

 

Yeah. Try another ecu and see what happens. Check the wires by the ecu also.

 

Pull the valve cover and inspect all the valve springs, count the coils from top to bottom on each spring and make sure that one has not snapped and buckled in

 

Just had the head off. All of that has been inspected and is good. I have a new cam position sensor on the way to replace what I think is a faulty intake cam sensor. I'll update the thread when I figure this out.

 

just for ****s and giggles i know you inspected the coil wires, did you put in any dyeelectric grease inside the coil wires before reinstalling...other then that, what i would say is try changing out the ignition coil boots underneath the coils... sounds like uve gone through the motions... have you tested the idle air control valve...??

 

Yep dielectric grease on everything. The plugs are sparking, and there is fuel. It points to a timing issue, but the car is in time. I'm pretty certain I'm having a signal issue with the intake cam sensor. Yes I also tested the IAC. it is functioning properly.

 

Just and FYI, the new owner of my car figured out the issue. It was the injectors all along. One must have been sticking open or something, but it was not enough to notice anywhere but idle. Oh well, problem solved! The car is now making 450WHP on E85.