: 94 ETC intermittent/low RPM miss



CadiJeff
08-29-06, 12:03 AM
Already complete:
New plugs
New PCV
Cecked coil packs
Checked plug wires
Cecked fuel pressure
Cleared carbon from engine (at expense of neighbors nerves)
no powertrain codes showing

it dosn't act like a fuel starvation

remaining suspects:
vacume leak, not sure where (suggestions?)
semi-intelligent coil pack that knows when I am checking it
FPR again?!?
is there an ignition control module that could be bad?

due to all the carbon clearing though when it is not missing it runs smooth as glass.

Ranger
08-29-06, 10:12 AM
The ICM (Ignition Control Module) is what you plugged the coils on to.

You might try replacing the plug wires. With age, they are a much more common cause for your symptoms than the ICM.

CadiJeff
08-29-06, 12:09 PM
plug wires were replaced with AC delco wires a little over a year ago as standard maintenance, they don't seem to be the problem.

CadiJeff
08-29-06, 12:15 PM
Could the egr valve/tubes becausing this? If so what is the procedure for checking/cleaning them on the old 94 n* intake manifold setup?

also, would a vacume leak somewher cause this? I think I keep hearing an air hissing sound from the passenger side of the engine compartment but I can't pinpoint it, it dosn't seem to be comming from the pcv assy. What else is on that side?

dkozloski
08-29-06, 12:16 PM
Raise the hood on a dark night with the engine running and mist some water on everything with a spray bottle. If there is a problem with the spark plug wires you'll see it.

dkozloski
08-29-06, 12:20 PM
Could the egr valve/tubes becausing this? If so what is the procedure for checking/cleaning them on the old 94 n* intake manifold setup?

also, would a vacume leak somewher cause this? I think I keep hearing an air hissing sound from the passenger side of the engine compartment but I can't pinpoint it, it dosn't seem to be comming from the pcv assy. What else is on that side?
When looking for a vacuum leak, spray some starting fluid around the intake system with the engine running and see if something changes. When the starting fluid gets sucked into a leak the mixture richens and the engine speed changes. Keep your head back so you don't lose your hair and eyebrows.

Ranger
08-29-06, 04:28 PM
Could the egr valve/tubes becausing this? If so what is the procedure for checking/cleaning them on the old 94 n* intake manifold setup?

also, would a vacume leak somewher cause this? I think I keep hearing an air hissing sound from the passenger side of the engine compartment but I can't pinpoint it, it dosn't seem to be comming from the pcv assy. What else is on that side?
Check the intake cover perimiter.

JimLucky
08-29-06, 07:46 PM
? If so what is the procedure for checking/cleaning them on the old 94 n* intake manifold also, would a vacume leak somewher cause this? I think I keep hearing an air hissing sound from the passenger side of the engine compartment but I can't pinpoint it, it dosn't seem to be comming from the pcv assy. What else is on that side?[/QUOTE]

There is a vacume line that runs from the throttle body all the the way across
the engine to the pasenger side firewall for the CLIMATE CONTROL heat/ac.At the firewall
another line branches off to the vacume reserve canister wich is in the front passenger wheel well.

Ranger
08-29-06, 08:09 PM
Yes, that line is the supply line for the cabin (HVAC & parking brake release). It runs from the firewall to the reservoir, where there is a check valve then to supply (intake manifold). I think the reservoir is under the battery. They have been known to crack. Also, obviously check the hoses.

The best thing to do is use a stethescope (or rubber hose). A vacuum leak will sound like a hurricane.

CadiJeff
08-30-06, 12:03 AM
The only sound I hear out of the ordinary is a slight hiss on the passenger side near the power steering pump. the cover torx bolts are tight to spec, could the egr cause this?

CadiJeff
08-30-06, 12:04 AM
this is starting to get real annoying.

dkozloski
08-30-06, 09:18 AM
Another technique I use to find the source of vacuum leaks is to go around with a pair of needlenose pliers with the engine running, squeezing the hoses to see if I can make something change. Sometimes this will give you a clue.

Ranger
08-30-06, 02:45 PM
I doubt it. The EGR is on the drivers side.

CadiJeff
08-30-06, 07:26 PM
I doubt it. The EGR is on the drivers side.
not what I meant, I meant the symptoms in general

Ranger
08-30-06, 08:10 PM
I think it is possible. There should be no EGR flow at idle. If there is, it would cause idle problems. That said, if it where the case, I think it would set a DTC.

CadiJeff
08-31-06, 02:20 PM
as annoying as this is its not like the car owes me much at 209000mi

CadiJeff
09-03-06, 02:56 AM
Hey Ranger, do you think having 3 spark plug wires that light up along their entire length intermittently could be causing my problems? found that tonight, it was really quite interesting to watch.

Ranger
09-03-06, 09:35 AM
Probably. Mist the wires in a dark place. If you see the wires arcing, replace them. The corona (that I think you are taking about) is normal.

CadiJeff
09-03-06, 12:50 PM
If it is normal then why is it only the same 3 wires? On the other side the problem seems to be getting worse, this could be a good thing as it may be getting easier to diagnose as it gets worse. My thought is, that it is still a defective/malfunctioning coil pack(s), and I just havn't caught it(them) at the right time. I would have a hard time believing that the 15 month old ac delco spark plug wires are the problem, and most any other problem I can come up with would set a code and there still are none.

Ranger
09-03-06, 04:40 PM
Well, if you suspect a coil, borrow a known good one from another car and swap them, one by one. If you get a big improvement on one, then buy a replacement.

CadiJeff
09-04-06, 12:57 AM
If it is a coil it is being slow and inconsistent to fail.
But I have a new suspect, problem is I don't know what the hell it does. I found two cracked vacume line rubber boots, the first one is on the top of the throttlebody assy. and consists of 3 holes with the middle one plugged presumably by the factory. the other is at the other end of one of the hard vacume lines comming off of the first boot, it plugs into a ...something, some kind of small (approx. 2inX2inX2in) box with 1 wireing harnes that has 2 or 3 wires, this is attached to the rear valve cover, this boot was so badly rotted that it fell apart into 3 unusable pieces upon inspection. could this be the source of my problem? What does the box do?

Ranger
09-04-06, 11:09 AM
Those cracked vacuum lines most likely are your problem. The box you discribe sounds like the EVAP system purge valve. It stores fuel vapors in a canister and burns them on start up. I would expect it to have set a DTC.

CadiJeff
09-04-06, 09:14 PM
well unfortunately it didn't/hasn't set any codes. I'm not sure that it is part of the evap system as ther are no fuel lines, just the vacum lines and the wires.....hmmm

Ranger
09-05-06, 12:06 AM
EVAP = Evaporitive Emissions System. There are no "fuel" lines. Only fuel fumes. It keeps the gas fumes from evaporating to atmosphere and burns them. The fuel system is a closed system per the EPA.

CadiJeff
09-05-06, 01:16 AM
and you think this would cause my miss........cool.......now would the dealership have these vacume line boots or will I have to go to a salvage yard, if it is option two should I snag the whole box assy. and lines?

Ranger
09-05-06, 09:34 AM
Well, I am not sure it would cause a "misfire", but it's possible. You need to fix it anyway, so see if that helps. Dealer should have what you need, but the bone yard will be cheaper. If you go there, you may as a well snag the whole assy.

JimLucky
09-07-06, 03:36 PM
Please read this thread on VACUME LINE HARNES

http://www.cadillacforums.com/forums/northstar-performance-technical-discussion/83772-help-identifying-parts-removing-wire-harness.html


I know the vacume line part you are talking about on the throttle body mine was cracked also.The parts department had to show a digital picture I took of the vacume line harnes and pass it around to the mechs at the dealership.I had to order the whole harnes to get the part I needed and it also came with the Map sensor installed in the harnes its well worth geting the whole harnes.

Hold on and I find the #

OK Keep in mind this part # was for a 93 eldo N* vin 9

Description: Harnes A, part #3535716

Price $95
The complete vacume harnes with rubber boot to top of throttle body wich
included MAP sensor installed on the vacume harnes.

A vacume leak would cause your RPMs to fluctuate during idle and a late throttle respone.But you have to have the basics working first before you go any further with cylinder miss diagnostic.The missing could be a defective
new spark plug or defective new wire.
If it was me I would repair the vacume leak then test drive and if there is still a miss I would remove and inspect the new Spark plugs looking for a electrode problems or a black carboned plug and replace if required.Also check
the gaps.If any one plug didnt look perfect in burning color I would replace it.