AT wits end- 85 3.2 rough idle

[mackskibum]

OK gang- I have spent about 2 hours reading all the posts related to rough idle- I'm stuck.

Please read carefully- I have done a bunch of legwork and testing already. I'm not looking for ready-fire-aim help here. I think I have exhausted the most common issues. I can safely assume based on my testing that it is not a vacuum leak, fuel filter, cap, rotor, plugs, injectors, O2 sensor or the like. It has to be deeper than that.

Here's what I have done so far:

Top end rebuild, new rings, new exhaust valves, cat bypass 300 miles ago. Uses no oil at this point, and I would consider the rings seated and overall engine condition is excellent.

Leakdown 2-3% across all cylinders

Replaced all intake gaskets and spacers due to a "mistake" at initial reassembly, no leaks at intake.

Injectors have been tested and cleaned on an ASNU machine. Two are new Bosch due to leaks.

New O2 sensor

Cap, rotor, plugs new since rebuild.

Rubber 90's on the fuel pressure regulator and fuel pressure stabilizer are new as well as the "Y" connector on the manifold. All diaphragm items like the regulator, stabilizer, and brake booster have been tested for leaks- all OK.

Other lines to oil tank, thermal switch, etc have all been verified as good.

Fuel quality switch on DMEis at pos. 0

Ground connections on manifold are tight.

No corrosion on multi-pin connectors in engine compartment.

Idle swicth is actuating and pin 2-pin 5 shows .09 ohm resistance (is this acceptable?)

Plug wires are Clewett's from our host and tes OK.

CHT resistance is OK, and is 3 wire type 2 years old.

ICV operates- you can feel it vibrate with key on, I cleaned with carb cleaner and tested on bench, does actuate both ways when power applied to the appropriate pins.

Here's the symptoms:

Runs great above idle. Good power and performance driving. No steady throttle stumble or hesitation.

Cold starts are great. Idles at 1000 RPM for about 90 seconds, then idle drops and becomes lazy. I wouldn't say there is a miss- its just rough. The idle (according to the dash tach) goes to 600-700 as soon as the O2 comes on line.

Disconnecting O2 causes smoother operation. Disabling the ICV brings idle up a little. If I adjust the base mixture at the AFM, i see very little change in adle quality. Changing the idle speed via 7mm adjuster brings idle up a little, but as soon as you connect ICV and O2 it goes right back to the rough symptom. It almost seems as though if I could get the idle up to 800-900 RPM, the roughness would be gone. The problem is the system takes over and drops it right back down to where I started.

Thanks for your help!!!!

Dave

[stlrj]

"It almost seems as though if I could get the idle up to 800-900 RPM, the roughness would be gone."

How about raising the base idle speed?

Joe

[mackskibum]

Joe- did that, as soon as I hook the O2 back up, and enable the ICV, the idle returns to its prior speed and quality.

Dave

[MAS956]

Have you checked for an air leak at the oil filler cap?

[mackskibum]

Thanks Mark- I will check that- the cap is new, though and I can hear a change in idle when I emove it.

I am thinking that I have something else going on- maybe an AFM problem or DME issue. rather than an engine sealing issue.

[Nashville84Cab]

Do you have a performance chip in the DME? If so, did you unhook the brown DME wire (under driver's seat)? This seemed to smooth out a number of rough idles including mine. Look at 911 Chips website and you will see Steve Wong's info on that brown wire.

Good luck and at the very least here is a free bump!
Darrell

[mackskibum]

Darrell- no performance chip, brown wire is disconnected. I did connect it to see if it made a difference- no change.

Thanks for the bump.

[JeremyD]

intake leak? spray some brake cleaner to see if you have any idle fluctuation.

Check your brown wire at the DME box.

Clean your ground strap at the transmision.

How many miles on your injectors?

Have you checked your voltage?

[DW SD]

Do you have the reducer cone in the breather line to the oil tank? That reduces the potential impact of a vacuum leak at the cap.

How about your idle switch - what is the resistance when the throttle is open?

[911quest]

Did you opt. for a lighter flywheel with the engine rebuild??

[KFC911]

Originally Posted by mackskibum

...ICV operates- you can feel it vibrate with key on, I cleaned with carb cleaner and tested on bench, does actuate both ways when power applied to the appropriate pins.

Here's the symptoms:

Runs great above idle. Good power and performance driving. No steady throttle stumble or hesitation.

Cold starts are great. Idles at 1000 RPM for about 90 seconds, then idle drops and becomes lazy.

I'm not expert, but your symptoms are very similar to what I had some time back. Cleaning my ICV improved things somewhat, but it wasn't until I replaced the ICV that my idle problems totally disappeared. How old is your ICV, and do you have access to a "known" good one to swap and try? I tend to think of the ICV much like a DME relay...you're eventually going to need one, so I eventually bit the bullet, and that was indeed the final solution in my case. Good luck...in the meantime, you get to practice heel & toe while at the stoplights

[mackskibum]

Jeremy- thanks for the input, but please read the posts and responses.

All vacuum leak possibilities have been investigated and all rubber parts replaced. I am not new to this issue on the 3.2. The only one I haven't checked is a leak at my new oil cap.

Brown wire- see post by Nashville 84 and my response.

Ground strap- good call, but was cleaned prior to my reinstall of the engine after the top end rebuild.

Injectors: as posted in my original background/question, injectors were cleaned and tested on an ASNU machine. 4 tested fine after cleaning, remaining 2 were replaced with new Bosch 158's.

Voltage is a steady 13.5 with engine running regardless of load. VR has less than 1000 miles on it. This issue has been in the backof my mind for a while- what may have been damaged in the failure of the VR? Mine was catastrophic-it took out the clock, alarm module, tach, speedo, turn signal relay and DME relay. All of these items have been replaced since then. For a time reference, everything replaced on the car since I have owned it was after the VR failure- it happened on my drive home after purchase. Could this have damaged the DME, and how would I tell?

DW

Reducer cone is in place.

Idle switch is completely open when off idle. I am still wondering if my resistance reading at the DME for the closed switch is too dirty for the DME to read a path to ground.

Nine9

No WUR- 3.2 Carrera

911 Quest

No- stock flywheel- I would have expected a lopey idle if I had changed the flywheel or cams. Engine is stock.

KC

The ICV is original as far as I know. I was trying to avoid throwing $175 at this just to find out if it is good or not. I do not have a known good unit to test with. I have tried the "bench test" procedures from other posts, and electrically the unit operates, and it will slam open and shut mechanically. Any thoughts on a good functional test procedure? I can drive an NPN PWM signal, but I am guessing that this is PNP.

Keep 'em coming, there are a couple of possibilities listed that I need to check, but I am beginning to think I need professional help...

[Javers]

Its a longshot, but have you verified the ICV can rotate through its full movement? The reason I ask is that I had a idle hunting issue, couldn't find the problem until I actually opened up the ICV by bending back those little tabs and removing the whole outer casing. What I found is one of the magnets had cracked, preventing full movement. Once I cemeted the magnet back together and re-installed, problem was cured.

Jon

[MAS956]

I know someone else has mentioned the AFM - have you had it apart to reposition the wiper arm over fresh substrate material?

[rallyracer]

Like KC911 suggests, if you come up to a stop sign and push the clutch in, do your rpms drop below idle and almost make the car stall? If so, then replace ICV. I would replace it anyway if it's original. I haven't owned one that lasted more than 6 yrs without issue, and the tests are sometimes inconclusive. You seem to be chasing a very minor issue. You could also wait until it gets worse for easier diagnostics.
David

[ianc]

I know you've tested the injectors and so forth, but I have to say I'm a bit skeptical of the 2 newies and the 4 oldies combination. I know these injectors are $$$$ but...

I had the six original 158's in my car. I pulled them and took them to be tested and they were pronounced fine. I replaced with six new 159's and the car exhibited better running characteristics; some have reported a better idle.

Just throwing it into the mix...

ianc

[Steve W]

84-86s don't as well as the 87s up because of the programming. Try sticking a DME or chip from a later car and you'll see what happens.

Otherwise, make sure you really have no intake leaks. Use engine starting fluid and spray all around the intake with the O2 and ICV disconnected. If the idle shoots up you have a leak. Second, adjust the idle CO to 0.6 to 0.8%. Finally adjust the base idle speed by jumping the B-C test terminal on the left side of the engine compartment and setting to about 800 rpm.

[84porsche9113.2]

Originally Posted by mackskibum

If I adjust the base mixture at the AFM, i see very little change in adle quality. Changing the idle speed via 7mm adjuster brings idle up a little, but as soon as you connect ICV and O2 it goes right back to the rough symptom.

Are you adjusting base mixture blind or are you using some kind of gas analyzer?

If you are adjusting things without an idea of what your AFR is you are basically doing it blind...

I myself had the same problems which went away after my base mixture was adjusted with the proper tools. It would help to have the proper tools to get the job done right, or hire out to a mechanic.

Since it looks like you've done everything else, my guess would be that it is your base mixture that is off.

Like steve said, make sure your base mixture is set correctly, then set idle by jumpring the terminals and adjusting the idle screw. I think those 2 things done correctly and in that order should solve the problem if you don't have any vacuum leaks or electronics issues.

But you can't do it without having a gas analyzer or an equivalent analyzing tool - won't work if you are trying to adjust the base mixture blind.

[KFC911]

[QUOTE=mackskibum;3448031]KC[/B]

The ICV is original as far as I know. I was trying to avoid throwing $175 at this just to find out if it is good or not. I do not have a known good unit to test with. I have tried the "bench test" procedures from other posts, and electrically the unit operates, and it will slam open and shut mechanically. Any thoughts on a good functional test procedure? I can drive an NPN PWM signal, but I am guessing that this is PNP.


Is there a Pelican in your area with a 3.2? It's so easy to swap out (and check), that I'd ask. I did all the "bench testing" too on my original ICV, and although it "tested OK", a new one was indeed the "fix". If your's is original, it's just a matter of time anyways imo.

[84porsche9113.2]

[QUOTE=KC911;3449206]

Originally Posted by mackskibum

KC[/B]
Is there a Pelican in your area with a 3.2? It's so easy to swap out (and check), that I'd ask. I did all the "bench testing" too on my original ICV, and although it "tested OK", a new one was indeed the "fix". If your's is original, it's just a matter of time anyways imo.

After troubleshooting this issue myself, I learned that the ICV's main purpose is to compensate for additional load on the engine such as the a/c, headlights, etc.

There is no need to waste $175 guessing if the ICV is bad. If you do the proper tests, you should be able to determine if the ICV is good. The procedures are in the factory manual.

Part of the test from the manual is to test the ICV is to start the engine with the a/c and lights on and terminals b&c jumpered. The idle at start up should be low b/c the a/c is on. Pull the jupmpers out and the icv should compensate and idle should rise. Turn off the car again, and pull the vacuum hose on the FPR off. Jumper b&c and turn the car on. The idle should be high. When you pull the jumper, the ICV should compensate.

Also the there are electrical tests for the ICV in the manual. Check the ohm specifications. As well as applying 12V (per factory manual) to the outside prongs alternatively, (and grounding the center). Arm inside ICV should rotate to each side alternatively as you move 12V to the other outside contact.