Hi all,


Question A.

My car runs good but it idles around 1200 rpm after the car has been fully warmed up.

I would like to adjust the base idle speed and idle mixture.

Do I have complete list of things to do before I make any adjustment? Any advice would be appreciated.

I have never done it before and I am just getting ready by reading our FAQ/Bentley manual.

Thank you as always.


1. air intake; check/replace air filter/air thermostat look for air leak

2. tune up; spark plugs, wire, cap and rotor

3. battery charge and fuel injection relay (Is this fuel pump relay? The white relay by the front passenger foot)

4. Check fuel supply

5. Check and clean MAF, Idle control motor and throttle body valve

6. Check O2 sensor

7. Check ignition timing




Question B.

With the battery disconnected, I am getting the following reading.

MAF platinumm wire resistance / 2.7 ohms

Idle mixture potentiometer resistance / .389 ohms

I turn the screw half turn, it changes to 389 ohms. The value does not move through the entire range. The value jumps up and down rather... Do I need a new MAF prior to my baseline idle speed/ idle mixture? The manual says it should be around 3.5-4.0 ohms. Oh, yes. I almost forgot. There is a hiccup as the engine rpm comes down to idle.

Hi All,

I swapped the MAF with a good used one. A few days later, the car runs much lower RPM at idle. Done!

As always, thank you.

--

Hi Phil,

I know you were thinking about this.... Hahaha.

Hi Sean! Long time no chat.

I know you are kidding that I remembered this post for two years!

What are you doing cleaning out your profile?

Two years later and you are SURE it was the AMM..... You are remembing the post of car symptoms and its fix far better than I!

It doesn't explain how it got all the extra air to run on.
We chased that for a bit didn't we!
Phil

Hi Phil,

Yes, I usually change one thing at a time so I can keep track of what goes wrong. I am 100% sure it's the AMM. With a lack of knowledge, I can't explain how but I am telling you what I did. :-)

I am a very private person. I don't like to leave my personal information on the web. Do you know what happens on the internet never gets erased? I mean everything even if you delete stuff from your mail box. Going back to somewhere in 1995. :0)

In the future, I would be more than happy to meet you in person. In Brooklyn or LA? :*)

As always, thank you.

39.245 dwell angle

Read the value at the ECU connector.

coolant temp sensor

5.03 ohms @ 41.7 degree F

Hi there again.

Seems your post dropped down pretty far down the list.
I clicked on the this post as it seems to be in the middle of the others.

Your question about using a dwell meter I cannot answer. I only know of using one of those on K-jet cars. I think it has something to do with the frequency valve, idle mixture and maybe the O2 sensor.
I never hooked one up to my K-jet to find out.

As far as the AMM those are the readings I have seen others have. I am not sure that any of those readings are conclusive unless there are totally out. Like a missing hot wire resistance.

That reading of the ECT seems super low in ohms at that temperature if that is the temperature of the coolant in the engine. That reading should be on a well warmed up engine that's closer to 190 degrees.
If the engine is that cold you should have a reading of a couple thousand ohms on pin two of the ECU connector.

43.5 degrees. That sounds digital?
I am more analog, You know, like the chill of the steel of a trunk lid or side of door with no sun on it. No other heat source, now thats the ambient treatment.


The Throttle Position Switch reading is from pin three. That seemed OK showing continuity to ground and then open. It grounds pin three to idle the engine. I just learned that from Art Benstien.


As far as setting the throttle plate, I would not have bothered counting turns of the stop screw.

You want that hose off so you can see the plate just barely move when the screw is screwed up to touch the lever.
I then give it only about one-third more of a turn upward and lock it right there.
The object is to have that plate to be as closed as possible but just stopped open just a wee tinniest bit. That way, any and all air, has to go through the IAC when it is turned back on or not grounded
It also creates the most vacuum at the side ports to operate the FPR and evaporative canister properly. Leanest FPR setting and brings in any spare vapors with a metered, the fittings, amount of air.
GOOD OLD VAPOR EMISSIONS, you gotta love them to burn them!

Then set the TPS to go click "just" when you push or turn the plate to open and click back when closed. The will time in the "transition space" from idle to running that the computer needs for program change. If there are no other air leaks the program will match that amount of air shift it will see momentarily from the AMM.


That black knob just helps you idle the engine, below the 750 rpm. The computer holds the 750 after you turn the IAC back on or not grounded
We might be only talking a fifty rpm difference but base idle setting is below the IAC range for the best response of repetitive 750 rpm idling.
As I said before, a clean and working IAC will race the engine up and settle it right back down every time you start the car. If the plate is too open too far, the engine will lag going down or never get there. As in your case.

Sometimes, I think that "black knob" is a curse to the LH's if its not closed when the IAC is turned off or grounded. It can get opened to far before the IAC gets turn back on. The engine should limp or be rough while its below and disconnected from the computers final idle specification. Just short of gasping for air kind of running. The knob should only let it do that!
That is the BASIC curb idle IS, hood up, with idle speed of the stop screw only, PRESET! No IAC.

The computer has the 750 rpm specification which is the "normal operation" idle speed of "driving" about town. Turn on the A/C or in Drive and it should not vary much. The IAC picks up the load as it should but still have some range going upwards. That is what you hear when you start the car. Load pickup capability.

You probably got it tweaked by the time you see this!
Phil

Hi Phil,

I did the coolant temp reading when the engine was cold.

Finally, I was able to give a tune up; plug, wire, cap + rotor. The car starts beautifully either cold or warm. It runs amazing when it's fully warmed up, so smooth.

I did two different vacuum leak tests done by using carb cleaner and burning incense. There is no leak that I can find...

Based on my testing, everything looks good. I must have missed something. I will revisit the throttle switch and swap back to old IAC to see if anything changes.

Thank you.

Reading values at the meter.

MAF platinumm wire resistance / 2.7 ohms

Idle mixture potentiometer resistance / .389 ohms



Reading values at the ECU connector.

MAF platinumm wire resistance / 3.0 ohms

Idle mixture potentiometer resistance / .5 ohms

Hi all,

Should I leave the throttle plate or do I need to make an adjustment? It clicks and seems like it's closed all the way... The linkage arm is a bit loose. Just follow the Bentley manual??? Thank you always.

Cleaned the plate, not stuck, all opening are clear and no slack on the liknage arm.


Read the value at the ECU connector.

Continuity when the throttle is closed

No continuity when the throttle is opened

I was reading over you planing posts and thought you are going at this very methodically!

I then blinked at your statement "It clicks and seems like it's closed all the way...The linkage arm is a bit loose." It was then I cocked my head and thought SEEMS, what could he be looking at or working with?

You want the bore wiped clean and any small bleed holes around where the plate seals cleaned out.

You want the stop screw backed COMPLETELY away and clear of the shafts stopping lever.

You want to feel for excessive play in the throttle shaft bores in the housing even if you have to relax the spring on the pulley.

You want to feel that the plate is held tightly by the shaft, they usually are, and it fits centered in the bore all the way around in there.

After getting a confirmed fit, you set the stop screw up against the shafts lever just enough to barely wiggle it and not open it any appreciable amount. It's an anti stick in the bore stop screw, not a throttle opening setting. The most I turn it is about one-third turn after "I think" I saw the plate move.

The idle/run throttle switch has to be set by twisting the shaft only and the last thing is to make sure you turn the body of the switch towards the close plate position, counter clockwise from the drivers position or from rear side of the engine before tightening the two screws down. The play in the switch contacts and the plate opening is the allowance of timing between pickup of the ECU to change programs, to the airflow changing. If that makes any sense.

If any of this is done with reasonable accuracy the throttle idle speed will be in range of the IAC's vane volume. If that makes any sense.

The engine should idle lower with the IAC grounded by the connector wire on the fender and rise slightly when released and settle back, as if you just started the car. But do not hold me to that in that to how much, as I do not know every car. I just listen for that motion to know I have a good working IAC when it's started over many times.

You said you were fighting a droop on idle down. I am wondering if it a worn throttle shaft with some air leakage is a cause as rare as it must be on these cars! The adjustable linkage that goes back to the pulley should only swivel and rotate freely but not interfere with either of both stops touching down distance. The throttle shaft or pulley stop need to hit each other at the same time. The swiveling play or lack of slack is all that's allowed.

If there is Some Slight Slack, its going to be in the throttle cable over the pulley drum. It is a must that the stops work as they are intended too! Not influenced by engine twist or thrusting forward or rearwards. Cables must move freely inside their sheaths from the pedal and do wear, albeit very slowly!

FYI an old mechanics trick on carburetor cars was to reset the throttle tension springs before or after tune-ups to make the owner think the car was more powerful. Done over a little time maybe several oil changes tighten up the spring a wee bit. Talk up a tune-up later again and magic would happen all over again! Even if it was just some new additive for this or that.

Release the spring tension, put the ole-safe crackers feel on that shaft and ponder the idea just a wee bit. It could be cruddy?

Keep up the effort there in some good weather, I hope!
Phil

Hi Phil,

I have decided not to log in because then I wouldn't be able to read your comments.

Thank you for your detail description. I am getting ready and collecting parts/info but I will report back with question.

Should I make a cheap smoke detector using a cigar? For sure, I can't say there is no leak.

To clarify regarding the adj linkage play, there is a slight play/slack in between the metal ball and the plastic linkage housing that holds it. Maybe it's normal or maybe it got stretched over the years.

Thank you as always.

I do not what is going on with your profile.

It shows you as who you are and yet you posts go both ways.

Claiming to be or having a reserved profile. Either is looking screwy..... You might have two different passwords going on from some time past with the same handle name?




I think there will always be a tiny bit of slack. You just want to make sure the throttle plate is in fact closing with its stop holding just enough that it does not let the plate jam itself inside the bore from an excessive pulley spring setting pulling on it.
You do not want the throttle body over filling the below idle level travel of the IAC to where it, the IAC, will make the engine stay over revved if it ever became stuck fully open.
I think in most case the IAC works staying mostly closed and fails to open properly. Then someone comes along and fiddles with the throttle body to compensate for a bad IAC.

I think the "bendable" pulley stop is a back up or a redundancy. If the pulley moves open before the throttle opens within that "A" tiny bit of slack...its perfect. You just do not want the swivel ball linkage rod holding the pulley off its stop and lose that redundancy or again the rod and pulley holding the plate open.

That plate is placed right in an area of dissection of some air bleed holes in the aluminum body and while it rolls open it affects air flow "transition" of the idle characteristics along with the TPS prompting the IAC and the ECU programs to an "above idle operation."

The vacuum bleeds have Most to do with the evaporative canister for emissions any other accessories ported on past cars. The basic idle procedure has stayed the same, throughout, to maintain complete throttle down for safety.

I guess this is why I stress over reading about the symptoms so much.
When it does not work right you stress over it like right now. One will drive with the brake ready or throttle pedal to be feathered.

Hope you get her dialed in. That when "she's" are worth keeping! (:-)

Phil

Hi Phil,

Please discard my profile as which I didn't even bother to fill in the blanks. To me, internet is like a digital tattoo and which can be unforgiving.

As you see I can create my own log in name without having my passwords. I just found out too. It doesn't matter to me as long as we have our conversation if you don't mind.

I believe I am very close to reading all data. I just need to give a tune up. It needs new plugs, cap, rotor, wire and air filter.

As you mentioned earlier, I might have air leak when you at these data. My AMM is a little weak but it seems it's still working. I am trying to figure out to make a smoke tester.

With the AMM grounded, I was able to drop 300 rpm by turning the idle air bypass screw. So it ran at 700rpm with the idle motor off. BTW, I took out the screw and cleaned, plug it back by counting turns and adjusted after that. Turned back on the idle control motor, it now runs at 900 rpm. It's little high but it's much better than 1200 rpm.

I tried to adjust the idle mixture using my dwell meter but it doesn't read at all. On my dwell angle screen, it indicated 0 value. I was able to get my dwell angle value at the coil/negative. Where do I go from here?

Thank you as always.

Hi all,

Through ECU?

It says to connect 2 and ground but do I need to drain the coolant?

Thank you as always.

Hi all,

between outer terminal / 42.5 - 42.7
between center and each terminal / 21.9 (this one is closer to engine)
between center and each terminal / 20.3 (this one is closer to strut tower)

I am assuming that this is passing value. I need your confirmation. Thank you.

Hi all,

Here is my reading. My new O2 sensor has 70k miles on it. I am assuming that it's still working.

O2 sensor voltage / fluctuate between from .3 to .8 volts

O2 sensor heating element resistance / 8.4 ohms

O2 temperature

@ body 404 degree F
@ body connector 427 degree F
@ body by the wire 178 degree F
@ 4th exhaust manifold 280 degree F
@ 1th exhaust manifold 239 degree F