3.2 Hunting / Surging Idle Question

crashr · 06-28-2009, 07:22 PM

Hi folks,

I have just started experiencing a hunting / surging idle with my transplated 1987 3.2L engine.

I have done several searches but most of the time the issue seems to point to either the ICV or sometimes a cylinder head temp sensor. Today I swapped in a known good ICV and the car continued to idle eratically.

It seems just recently that the idle has gotten worse and at times will osccilate until the car actually stalls out. It also seems like the issue can happen when the car is cold or warm.

The other issue I found odd was that, when I took the oil cap off the idle steadies right out at 850ish. I would have thought this would have made the problem worse. Maybe someone can comment on why this is happening?

Also maybe someone else who has done a 2.7 to 3.2L transplant can comment if maybe I may have missed something in the vacuum line system that could cause the issue.

I do have one small braided hose from the front drivers fender (recirculation tank) that use to go to the charcoal box, but since I removed the charcoal box I normally just push it on the back of the throttle body where there appears to be an extra fitting about the same size. This seems to fall off alot, but even if I put it back on when the idle is hunting it has no effect.

I think that covers about everything I can recall about the issue.

Suggestions?

Talewinds · Talewinds's Garage

idle bounce

ICV usually seems to be the logical and reasonable place to start, but in actuality there are about 8 specific and solid possibilities that can cause it. Unfortunately you just have to start isolating and working away at them.
Can you describe your symptoms further with more detail?
And, here's a thread idle bounce , in it details how I fixed my particular issue with idle bounce.

kidrock · 06-28-2009, 09:48 PM

IIRC, a "rich" condition in your air/fuel mixture will make your idle "hunt" as you've described. When you remove the oil cap, it creates a vacuum, which sounds as if you are "leaning out" a possibly rich mixture.

Although there are several conditions which will make the idle hunt in your 3.2, I think this may be your problem. But, you want to try the easy remedies first.

aston@ultrasw.c · aston@ultrasw.c's Garage

x2 on the rich mixture.

You will need a wide band oxygen sensor or CO tester.

The adjustment screw is in the front left corner of the AFM (underside). The screw as a 3mm hex socket and is hiding at the bottom of a well. Originally there was a plug but mostly these are long gone.

IIRC the adjustment is counter intuitive: CW rich, CCW lean.

nhromyak · nhromyak's Garage

There is an idle speed switch.

I would think the O2 sensor would keep it within appropriate CO, unless of course, you're not running one. It could also be so far out, the O2 can't compensate.

crashr · 07-02-2009, 07:05 PM

I am not running an O2 sensor.

If I adjust the mixture screw does that not alter the fuel map used by the computer?

ischmitz · ischmitz's Garage

Check that your idle microswitch engages properly. A miss-adjusted throttle linkage will cause the throttle to stay a little shy of its resting and not engage the microswitch properly. The DME needs this switch to be closed to go into idle mode.

You can try to pull the throttle all the way shut and see if that improves the idle while the engine is running.

Also try do do this with the engine off. You should hear a faint click when the switch closes.

The idle bypass screw is to bleed air into the engine. It allows the ICV to stay close to its center positon to maintain a stable idle. The procedure is to center the ICV by putting a little jumper into the diagnostics port (same as closing the WOT switch). This will make the DME move the ICV to its center. Then you adjust for proper CO value with that screw.

I don't think this idle bypass screw is your issue. It doesn't become unadjusted over time. And since you apear to run rich you either have a bad CHT or some other problem. Removing the oil cap just lets more air into the intake through the oil tank.

Ingo

kidrock · 07-02-2009, 08:36 PM

OK, here goes...experts, please correct me if I'm off base.

If I understand correctly, the computer used by the 3.2 (unlike the newer generation ECU's) does not "adapt" or change it's mixture according to temperature, humidity or altitude changes. If the 3.2 mixture is affecting operation, 2 things will need to be checked and/or corrected:

1) check/adjust the air-fuel mixture, and
2) adjust the base idle.

This link should explain things a bit better for you:

idle bounce

good luck.

crashr · 07-02-2009, 08:45 PM

Hi Guys,

I appreciate your inputs.

I am quite certain the microswitch works properly as I hear it click when it closes.

I am going to work through the idle and mixture procedure that is listed in the threads above.

I do have on concern tha tI would like to address. I believe my alternator is on its last legs. It is fairly noisy and I think the bearings are worn. I have a rebuilt one just waiting to go in but I have been putting its installation off. Could this have an affect on a hunting idle that is temperature independant?

Thanks,

kidrock · 07-02-2009, 09:20 PM

I don't think so. But if it's on it's last legs, why don't you just go ahead and replace it? Put your mind at ease.

crashr · 07-03-2009, 09:05 AM

Hi Folks,

I jumpered the B&C test connection and the car idles perfectly (no hunting) but at 790-800 RPM. My understnading for an 87 is that this is far to low. I want to increase the idle, but I can't figure out how to turn the idle nut. What size wrench or tool does everyone use. Is it simply the nut that turns or the post as well?

vreference · 07-03-2009, 09:15 AM

I'm not sure why no one ever mentions it but, you might want to put a vacuum pump/tester on your fuel pressure regulators. Dashpots are not known for being reliable and when these fail, not only do the regulators no longer reduce fuel pressure properly but they also pump more fuel dirrectly into the intake via the vacuum line.

It'll take you 5 minutes and if they don't hold a vacuum you very likely found your problem.

Jee, why does my car idle so rich!?

crashr · 07-03-2009, 09:32 AM

Ok so my idle set screw is very badly stripped, and it was quite dirty. I have hit it with a few sprays of WD40, but a 7 mm socket just spins on it. Even when I use vice grips I cant seem to get it to move without having the tool slip. Any thoughts on what I should do?

Steve W · Steve W's Garage

Idle Hunting -- The problem continues!!

crashr · 07-03-2009, 11:39 AM

Ok now I'm really screwed. The 7mm nut was so badly stripped you couldn't even get a pair of vice grips on it. I tried to drill it out and broke and easy out and a drill bit in there, so now I have two peices of harden steel in the soft brass fitting. I honestly have no idea what I can do now to get it out. I have removed the idle set screw/fixture from another running car so I know what the entire peice looks like.

kidrock · 07-03-2009, 12:13 PM

remove the AFM as a unit, and have a professional drill and re-tap if necessary. Replace damaged screw.

ischmitz · ischmitz's Garage

I think he is referring to the idle speed adjustment. This is the screw on the throttle body and is for idle speed. Still, take the throttle body out and take it to a machine shop. Let them do the repair. Worst case you need a new throttle body but I think a competent machine shop can fix that. You don't want to drill it out with the unit in the car anyway. Metal shavings are the last thing you want in your intake.

The idle mixture screw is a bypass allen screw on the AFM. On a 3.2 with the AFM upside down it is easy to get to. It is on the underside of the AFM on the boss on the right side. There is usually a small blue plastic cap covering access. When you tighten it the air bypassing the flapper is reduced. It makes the flapper open more and hence the DME introduces more fuel (richer). If you loosen it more air bypasses the flapper and less fuel is delivered by the DME.

Ingo

crashr · 07-07-2009, 04:05 PM

Ok the machine shop was able to remove the idle screw and I have one on order. Does anyone know what torque the throttle body (4 bolts) should be tighened to? THey were quite tight when I took them off and appeared to have a white colored loctite material in the threads.

ischmitz · ischmitz's Garage

I don't know if there is a specific torque specification for these. They are M6, correct. I would simply tighten them with reason. Use a small rachet and twist it with thumb and index finger - don't crank like crazy. And if you want you could use blue Locktide to secure them.

kidrock · 07-08-2009, 08:53 AM

Quote:

Originally Posted by ischmitz

I don't know if there is a specific torque specification for these. They are M6, correct. I would simply tighten them with reason. Use a small rachet and twist it with thumb and index finger - don't crank like crazy. And if you want you could use blue Locktide to secure them.

+1. There really shouldn't be any specific torque value for these things. Snug it down, don't bust your balls doing it, and you should be OK. Personally, I have a little bit of an issue with using blue loctite. But I've been wrong before!!

BTW Dennis, thanks for the nice IM...sorry I wasn't able to respond, my computer is giving my family the fits. I just re-installed a Norton Security program, and it's acting like Hal2000