Stan.Shaw@Excell.Net

I had just driven @30 miles to pick my son up at the airport. When he called to say he was outside waiting, I restarted the car and noticed it was running rough but didn't give it much thought until I noticed it pretty much lurching at low speeds

I drove it home, and it seemed to have decent power and be ok at higher rpms. Being generally paranoid (or perhaps overly cautious) I didn't push it really hard, but I would not expect limp home mode to be so driveable.

I restarted it the next morning, but it was not improved. I did some searching and found the topic https://rennlist.com/forums/928-forum/433878-not-running-on-all-cylinders.html
so I followed the timing light test process, first confirming at least one wire from each dist was sending spark and then testing all 8 wires. Since the timing light showed spark to all cylinders, I am presuming I can rule out an electrical issue, correct?

The brief history on this car is that I acquired it less than a year ago and have had:
1. The intake refresh maintenance performed, changing effectively everything that is likely to go wrong using Dave Chamberland's list (thanks Dave).
2. I also had a complete timing belt service done.
3. I also had the fuel injectors cleaned and flow tested, and have confirmed their harness connections..
4. I put in new filters, plugs, caps, rotors, spark plug and coil wires (Magnecor), new ISV, new hall sender,
5. Vacuum line kit by Mark Robinson, with most, but perhaps not all connectors/elbows replaced.
5. I sent both computers to Rich Andrade to be reviewed (thanks Rich).
6. The MAF was rebuilt.
7. Ignition Protection Relay shows green light after a short time running
8. Spark plugs reviewed and they look ok.
The car has been running well for a few months including a round trip to SITM.

I suspect I should next review the mechanical timing status by pulling the timing belt covers. There was initially a glitch in the timing belt service where the belt was very loose setting off the toothed belt warning. This was resolved before the trip to SITM. I am not getting a toothed belt warning now.

I realize new parts can go bad, but am interested in whatever thoughts or suggestions the experts have that I should review next.

leperboy

Is the MAF the original? That's an easy check and could give you the symptoms you're having.

Matt

Stan.Shaw@Excell.Net

I will update my post, the MAF was rebuilt as well. Thanks.

worf928

Stan,

check for loose fuel injector harness connections.

Did Rich replace the hybrid in (rebuild) your LH?

Did you replace the cam cover gaskets? If so did you _replace_ the Hall Sensor?

Plug Wires? Coil Wires? (Those are new?)

Is the "protection circuit" tripping? (Red and/or Green LED next to EZK ECU.)

02 Sensor age?

Break out the unsponsored-on-Rennlist-but-purchased-by-the-OC special tool and see what it says.

WICruiser

Is the rough running condition only on start up or does it persist anytime that the engine is at an idle or low engine speed condition?

Generally it sounds like an intake leak such that at high vacuum conditions (idle and near idle) there is enough of a leak to make it lean, it could be only one or two cylinders making it very rough, that is small enough that at higher air flows and lower intake vacuum the lean condition is either compensated for or over shadowed.

Check the vacuum lines and listen carefully for a high pitch noise associated with a small leak.

Stan.Shaw@Excell.Net

Just checked electrical connections to fuel injectors and they feel firmly connected.

Hmm, confused about what you mean about "hyrbid in (rebuild) your LH". I sent my LH and EZK to Rich, he found no problems and sent them back. They were in the car when you put the Hammer on it and found no issues as well.

Hall Sender (per parts list $188 part) was replaced as were the cam cover gaskets (put pretty powdercoated covers on).

Plug wires and coil wires are new Magnecor.

On the relay, I noticed in another thread that it said it was above the computers. I am presuming (for whatever reason) it is below mine, as there is some type of relay there. I do not see any lights on. I will attach a photo to be sure I am looking at the right place. (irony here is that I put a bypass in on another car as a test, but am not positive I am looking at the right part... )

New O2 sensor, still in the box, waiting to be installed, as well as a temp ii sensor. So answer is that those parts are not new in the car yet.

Working on getting the software installed on a notebook PC, now that it is back in my hands

Will update list at top of this topic to include these updates.

Stan.Shaw@Excell.Net

It runs rough at low rpm but does not feel as rough at higher rpms. I am leaning towards that the problem is just being masked at higher rpms, but of course it does mean it is not magnified at higher rpms.

I am not sure I replaced all the elbows on the vacuum kit. It was a Mark Robinson kit that has since been decided had poor quality elbows in it. I bought replacements from Roger Tyson, but didn't find as many as Roger provided, so this could be a good direction to look further.

I have not noticed the whistling of an apparent vacuum leak though, but I will check again tomorrow.

dr bob

Stan--

Check the plugs. They may all be absorbing current, causing the timing light to fire. But one or more may be fouled, or may be lean. A check of plug color will give you more ammunition.

Alan

Stan - that is the protection relay and its normal location/mounting.

The relay disables half of the injectors not the spark so validate all your injectors are firing. That picture (if yours) looks like the green LED is on (one red, one green).

Alan

Stan.Shaw@Excell.Net

Thanks Alan, except the car was not running, the key was not even in the ignition. I think it is just a camera flash illusion. At least I know I am looking in the right place

BrianG

I'm in with this possibility. Sudden change.... only at low throttle settings (high vacuum state)...

Look for a detatched vacuum hose (or broken fitting).
Particularly look at the throttle-body vacuum ports (don't ask how I know about this issue)

Leon Speed

Good candidates are the vacuum line from the intake to the venturi Y fitting and the oil breather line to the oil filler neck.

Mike Frye

Stan,

I have no experience with the S4s, but when something like this goes wrong I usually do the old 'pull one plug wire at a time' thing. It can knock you on your *** if you do it wrong, but it will tell you if you've got one (or more) cylinder consistently not firing and it's quick and easy to do if your problem is consistent. If the idle changes when you pull one or more, you've found the culprit, now you've got to figure out what's missing (fuel, spark, compression). Mostly likely not a compression issue, so fuel and spark are most likely candidates if one's not firing.

Also, you mentioned the wires, caps, rotors. Are the coils old? What about a loose coil ground? I know you said this happened after a restart, but maybe something worked its way loose.



Actually I just didn't want to say what everyone else said, even though vac leak is the most likely. Just some more possibilities.

Stan.Shaw@Excell.Net

Thanks for the thought to do this. I pulled all the plugs and they all look similar, and using http://www.dansmc.com/Spark_Plugs/Sp...s_catalog.html they are all in good shape, only a bit of tan with no deposits.

Stan.Shaw@Excell.Net

I will review vacuum next, of course much of it is not easily visible. Is there a reasonable way to test much of this with a mityvac from viewable vacuum lines? I could just pull them off t fittings one at a time and see whether vacuum holds. Is this a viable course?

On a side note, how would I diagnose bad gas. I did recently fuel up and maybe the source was questionable...