Hugh

So I'd like some opinions on this idle surging issue I've been having with my '84 3.2L since my top-end rebuild. Here are the things that have been done to the engine:

* all valves & rocker arms replaced w/ new
* cams reground to "C2" spec by Elgin
* heads mildly ported - "just cleaned up"
* cat bypass
* B&B sport muffler
* K&N cone filter & intake adapter
* clutch replaced with (much lighter) Sachs Aluminum.

I have NOT yet replaced the chip.

The engine is fabulously revvy. I especially love the way it pulls after 4K - feels like a turbo. The problem is that whenever I return to idle, like when I've slowed to stop at an intersection, the idle almost always bounces a few times before settling. It bounces back & forth between 800 and approx. 1200 rpm. Maybe 1.5 bounces per second, if you can picture that. It doesn't always do it, but when it does, it'll bounce anywhere from 1 to 10 times before settling down. Sometimes, especially after a high-rpm/high speed run, it'll just bounce itself silly until I intervene with ever-so-slight pressure on the throttle. Obviously, it's annoying.

I've been thinking it was because I'd installed the lightened clutch without changing the chip.. that the engine is coming down off of revs more quickly than the chip is programmed to expect, so it intervenes, thus bounce. But if that were the case, wouldn't the severity of the bouncing be more consistent? Why would it go nuts after high speed runs? These questions are leading me to think maybe it's the idle speed regulator unit. But if that were the case, why would this problem have come up only after the rebuild and all these other mods?

I don't really understand how the idle speed thingy works. But it could have been screwed up beforehand without exhibiting this bouncing because before the rebuild I had some serious intake leaks, and settings and the way things were working were much different. For example, the idle speed screw was out way further then to get 800 rpm idle.

Anyway, I'm wondering if anyone thinks for sure it's the idle speed regulator. If so, I may swap it out this weekend. If not, maybe I'll just wait until I get a custom chip (which is inevitable, just too costly to do now), see if that fixes the problem, and if not then start messing with the idle stuff.

Thanks in advance!

DJB

Sounds like a nice rebuild Hugh.

I had a similar problem whcih bugged me for weeks. It ended up being the idle microswitch, which was intermitently failing.

Just a thought.

BER

Hugh,

I suspect that the ISV may be part of your problem. The ISV is not cheap, but they do go bad and eventually need to be replaced. You can try removing the ISV and spraying carb cleaner into the valve and see if that helps stabilize the idle.

I recall when I purchased my '84 Carrera about 5 years ago, it had an irratic idle and it surged while driving. I installed an Autothority chip, K&N Cone airfilter, cat by-pass pipe and Danske sport muffler. My irratic idle and surging were still there.

I then began to attack my idle and surging problems by taking the following steps:
-cleaned all chassis and engine ground connections (there are a lot!)
-complete tune-up (plugs, filters, cap/rotor, valve adjustment, etc.)
-replaced the O2 sensor
-updated my cylinder head temp sender to the new 2-wire type
-replaced the ISV
-leaned my idle mixture, because the mixture adjustment screw had been set to full rich

As a result of the above steps, my irratic idle and surging were eliminated. I can't say which remedy fixed the problems, but as a whole, they did the trick. Car now runs great and is a joy to drive.

Hope this helps. Bruce

Jdub

Sounds like you did not have the CO2 adjusted to me. That has to be done after the changes you have listed; the oxy sensor cannot cover all the possible variations, only those *around* the setting.

Jw

Hugh

Thanks guys. I have a couple more questions. What exactly does ISV stand for? Idle Speed Valve? And is that the unit located on the outside of the engine, the valve that bypasses the throttle body?

Is the "idle microswitch" something different? If so, where is that located?

And how does one "adjust the CO2?"

Thanks!

BER

Hugh,

The "ISV" is actually called the Idle Speed Stabilizer Valve. It is located in front of the air flow meter; right in front of you as you look at the engine. One of the easiest components to access.

You adjust your CO level using the adjustment screw on the underside of the air flow meter. The adjusting screw is accessed from under the air flow meter. A metal cap may be covering the access hole if it has never been adjusted. I believe the adjusting screw takes a 3MM allen wrench. To enrichen the idle mixture, rotate the allen wrench clockwise (but, remember the adjusting screw is upside down). To lean, rotate counter-clockwise.

Kind of hard to describe the throttle micro switch...never had to adjust it. Maybe someone with first hand experience can help you on that one.

Bruce

Hugh

Okay, I've seen where all this stuff is (except the "idle microswitch" - can anyone say what that thing does?). Wouldn't I want the car on some kind of sniffer to adjust the CO2 in order to get the right idle mixture? And if I did, what would my target be, in what units, given the mods I have? I wouldn't think it should be tuned to factory spec at this point.

My mech did comment as he had it on a sniffer that it was well below smog requirements, even w/o the catalytic converter. I don't know what unit we were looking at, but it was reading 33-34 ppm at a warm idle.

I'll definitely give the ISV a blast of carb cleaner this weekend, and look into the possibility of replacing it. It would help me a great deal if someone could explain how the thing works. Thanks guys!

Cheers,

DJB

The idle switch is on the throttle body it provides the closed throttle signal to the DME.

Mine was intermitently faulty causing surging. Here's a pic
http://boards.rennlist.com/upload/idleswitchpic.tif

Here is Bentley's test procedure:

NOTE - A defective idle switch (open circuit) will cause high idle speed (approximately 1,200 rpm) and advanced ignition timing (12°
before TDC)
-To test idle switch mechanical setting:
.Attach strobe type timing light according to manufacturer's instructions.
.Start engine and allow to idle.
.Open throttle plate approximately 1 mm while watching idle microswitch contact lever.
.Throttle switch should open before throttle plate begins to open.
.If switch is working idle speed will increase approximately 500 rpm and ignition timing will advance to 12° before TDC.
~ To test idle switch electrically:
.Engine should be stopped. Remove harness connector from switch.
.Connect ohmmeter leads to switch terminals (42 and 44). .Open throttle approximately 1 mm.
.There should be continuity with throttle fully closed and no continuity in all other positions.
-To test idle switch harness and connector:
.Start engine and allow to idle.
.Disconnect idle switch harness connector.
.Engine speed must increase approximately 500 rpm.
.If engine speed does not increase check wiring to ECM. .If no problems are found replace ECM.
-To test decel fuel shut-off function:
.Start engine and allow to idle. .h r- .Disconnect idle switch harness connector and bridge a
ness terminals.
.Raise engine rpm to 1,300. ning .Engine should start surging, indicating injectors are tur
off. If not, check wiring between switch and ECM. be .If no problem is found with switch or wiring, ECM may faulty.

DJB

Here's a Pelican diagram of the idle switch
http://boards.rennlist.com/upload/idleswitch1.jpg