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Frustrating intermittemt idle problem on a Formula by Rich Truett
Started on: 04-26-2015 07:09 PM
Replies: 19 (388 views)
Last post by: Gall757 on 06-06-2015 05:36 PM
Rich Truett
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Report this Post04-26-2015 07:09 PM Click Here to See the Profile for Rich TruettClick Here to Email Rich TruettSend a Private Message to Rich TruettEdit/Delete MessageReply w/QuoteDirect Link to This Post
If I could just solve this one problem, my '88 Formula would be running fine.
I need expert help here.
Car: 1988 Formula, automatic; 55,000 miles.
Items already replaced: ICM, MAP, 02 Sensor, CTS, plugs, cap, rotor, wires, EGR valve and tube, IAC, fuel filter, thermostat.
Trouble codes: NONE.
The problem:
When the car is cold, it idles fine.
When the car reaches operating temperature and I approach a red light and come to a complete stop, it idles down to around 900 or so RPM. It idles fine for about 20 seconds.
Then the fun begins.
The engine slowly starts idling down and until it almost dies, then the RPM jumps to 1100 or so and it starts idling down again. Sometime it does stall. When the idle jumps back up to 1100, the engine sounds like it is laboring, as if the timing has been advanced or something.
I tried resetting the IAC as per instructions on the forum. No changes.
I have not checked the fuel pressure.
There are no vacuum leaks.
With the IAC disconnected, I set the idle using the screw and the "minimum air" setting. The car will not idle below 800 RPM.

If anyone can help, I'd greatly appreciate it.

Rich Truett
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Gall757
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Report this Post04-26-2015 08:00 PM Click Here to See the Profile for Gall757Send a Private Message to Gall757Edit/Delete MessageReply w/QuoteDirect Link to This Post
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Rich Truett
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Report this Post04-26-2015 08:14 PM Click Here to See the Profile for Rich TruettClick Here to Email Rich TruettSend a Private Message to Rich TruettEdit/Delete MessageReply w/QuoteDirect Link to This Post
Yes. I adjusted the idle set screw according to the instructions here on the forum...
If everything is working properly, no exhaust leaks, no EGR leaks, and the engine is properly tuned, you can go through the IAC system.

Idle is controlled by the IAC valve (idle air control) via the computer and is not adjustable.

You can go over the system if your not happy with where it is idling. Proper idle for the V6 is roughly 900 RPM.

The set screw in the throttle body is for minimum air flow through the throttle plate which is often misunderstood as the idle screw. Any tweaking of the throttle stop screw will give the ECM fits. The ECM wants to be in control of the idle and is not happy when it can't control it. If the normal learn limits of the ECM are exceeded, they will be reset to nominal, causing an erratic idle.

The IAC and associated passages need to be clean to work right. Remove the IAC carefully. You can clean it (the nipple) using carb cleaner and a small brass brush or rag. At this time also clean the throttle plate. Once clean, install the IAC back in the throttle body and reconnect the IAC wires.

For the ECM to properly control idle, the throttle stop screw must be set for "minimum air." This is a process that sets the idle with the IAC fully extended.

-- To fully extend the IAC, jumper ALDL pins A and B together (just like when you check codes) and turn the key on, but do not start the car.
-- With the key on, not running, and in diagnostic mode, the ECM will keep trying to fully extend the IAC. After 30 seconds or so, pull the IAC connector off the IAC *before* doing anything else. This will capture the IAC fully extended.

-- Now pull out the jumper in the ALDL, and start the car.


-- Typically the "minimum air" idle speed is in the 500 RPM range. I find the car can barley run at 550. So as long as you can get it to idle on its own between 600 & 700 your good. Set the idle using the throttle stop screw. (The engine should be fully warm to do this.)

-- Now shut the engine off and reconnect the IAC wires. The ECM does not know where the IAC present position is, so pull
the ECM fuse (or disconnect the battery) for 20-30 seconds. (This will cause a complete ECM reset of all learned parameters, including the learned IAC ones. Then reinstall the ECM fuse/Hook up battery.

-- Turn the key on, wait 10 seconds or so, and turn the key back off. This will now reset the IAC to a known key-off "park" position.
--Now start the car. The engine should idle properly under control of the ECM. There are some learned values, such as an IAC offset for A/C, etc that need to be learned, but this will happen under normal driving conditions.

-- I suggest driving the car right away under all conditions. Stop & go, steady cruising over 45 mph, full throttle, and so on. Pull over a few times and turn the car off, then restart it. The IAC can only learn X amount of counts with each run position. If everything else on the engine is in good condition and operating properly it should be around 900 RPM after coming to a complete stop with slight variations and improve over time.
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Gall757
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Report this Post04-26-2015 08:24 PM Click Here to See the Profile for Gall757Send a Private Message to Gall757Edit/Delete MessageReply w/QuoteDirect Link to This Post
Have you unplugged the TCC? It's a long shot, but it may be part of the problem.
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Rich Truett
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Report this Post04-26-2015 09:34 PM Click Here to See the Profile for Rich TruettClick Here to Email Rich TruettSend a Private Message to Rich TruettEdit/Delete MessageReply w/QuoteDirect Link to This Post
I have unplugged the TCC.
I'm flummoxed.
I've tried everything.

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Gall757
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Report this Post04-26-2015 10:02 PM Click Here to See the Profile for Gall757Send a Private Message to Gall757Edit/Delete MessageReply w/QuoteDirect Link to This Post
Got a spare ECM?
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rourke_87_T-Top
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Report this Post04-27-2015 10:46 PM Click Here to See the Profile for rourke_87_T-TopClick Here to Email rourke_87_T-TopSend a Private Message to rourke_87_T-TopEdit/Delete MessageReply w/QuoteDirect Link to This Post
just a guess here, I didn't see you mention the pick up coil, if it's very old a new one would make a huge difference, also the TPS Throttle Position Sensor has caused me the same sort of intermittent stalling issues.
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Rich Truett
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Report this Post04-27-2015 11:16 PM Click Here to See the Profile for Rich TruettClick Here to Email Rich TruettSend a Private Message to Rich TruettEdit/Delete MessageReply w/QuoteDirect Link to This Post
I have not changed the coil or tested the TPS.
Perhaps I can test those without buying and replacing parts that are still good.

My plan now is to make a ground to the engine and also to put some additional heat insulation under the ICM and see if that makes any difference.
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Patrick
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Report this Post04-28-2015 12:45 AM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Rich Truett:

My plan now is... to put some additional heat insulation under the ICM and see if that makes any difference.


No, just no. The last thing your want to do is to "insulate" the ICM. The ICM is damn hot when operating, and it needs plenty of air circulation around the base of the distributor to help keep it cool..

 
quote
Originally posted by Rich Truett:

My plan now is to make a ground to the engine...


Good grounds are important. I also discovered that good hot connections are critical as well. The following might make more sense if you read the whole thread.

 
quote
Originally posted by Patrick HERE:

About a year ago, I swapped out the pulley on the harmonic balancer and installed a "power pulley". (Hey, I got it for a song.) It's basically a smaller pulley that turns the alternator and the water pump a bit slower, therefore saving a little more HP for the wheels... as the theory goes. Anyway, I noticed that the idle quality had been affected right away after installing this pulley. The idle would often surge up and down a couple hundred RPM or so while at a light, whereas it had been rock steady prior to changing the pulley.

The reason why I mention this, is that after messing about with this other issue, the surging has now been eliminated.

I suspect there's a connection somehow... or maybe I should say a bad connection. I also suspect that Electrathon is reading this and thinking to himself... "I told that guy what the problem was."


It seems to me that my Formula's idle quality was being affected by a poor positive connection at the main power junction... which was exasperated by the installation of the power pulley which produces less voltage (or amperage?) at idle.

[This message has been edited by Patrick (edited 04-28-2015).]

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Report this Post04-28-2015 01:59 PM Click Here to See the Profile for 2.5Send a Private Message to 2.5Edit/Delete MessageReply w/QuoteDirect Link to This Post
TPS is my guess.
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Rich Truett
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Report this Post04-28-2015 08:12 PM Click Here to See the Profile for Rich TruettClick Here to Email Rich TruettSend a Private Message to Rich TruettEdit/Delete MessageReply w/QuoteDirect Link to This Post
I replaced the coil tonight.
That wasn't the problem. But since it was only $17, I am cool with it. The original coil has been baking above the crossover pipe for 27 years.
So, when the engine is hot, the idle jumps and the car sometime stalls when sitting at a light in drive.
Just for the heck of it, I disconnected the vacuum line off EGR valve. That also made no difference. The idle is still erratic. Interestingly, I applied a little vacuum to the EGR while at idle and more or less duplicated the inconsistent idle.

Next, I fiddled with the TPS. I unplugged and the idle surged to a steady 1500 RPM. I reconnected it and the idle stayed that high.
Just for the heck of it, I tapped the TPS with the end of a wrench and the TPS fell apart, came out of its socket. I put it back together and the idle is still 1500 RPM.

So, I will put in a new TPS tomorrow.

That would complete replacing nearly all of the sensors.


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Report this Post04-28-2015 08:23 PM Click Here to See the Profile for Rsvl-RiderSend a Private Message to Rsvl-RiderEdit/Delete MessageReply w/QuoteDirect Link to This Post
I've noticed that pictures I have seen of new IAC's (on ebay) show a thread sealing product on the threads. (a few also show some sort of washer as well) If you removed, cleaned and reinstalled the IAC without reapplying some sort of thread sealer could it be that it might be leaking vacuum around the threads?
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Report this Post04-28-2015 10:33 PM Click Here to See the Profile for tsharkSend a Private Message to tsharkEdit/Delete MessageReply w/QuoteDirect Link to This Post
...

[This message has been edited by tshark (edited 09-08-2018).]

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Rich Truett
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Report this Post04-29-2015 09:04 PM Click Here to See the Profile for Rich TruettClick Here to Email Rich TruettSend a Private Message to Rich TruettEdit/Delete MessageReply w/QuoteDirect Link to This Post
Well, that's it.
My car is unfixable and has to go.
I've tried everything and it will not idle in gear.
I bought it from a retired GM engineer, the one responsible for the 2.8's engine software.
If he couldn't even get the car running properly, no way I was going to.
I dumped another hundred in it replacing the TPS and coil.
And the symptoms remain:
When cold the car runs fine, idles fine. No problems.
When it is hot, say after 15 miles, the idle starts wandering and then jumping. Whenever it dips to around 700, it stalls.
Nothing I have done has improved the car.
I guess I'm done. I have two new shocks to install on the rear and then I am dumping this car, a white 1988 Formula on eBay.
My Fiero experience can be summed up in one word: Disappointing.
Thanks to everyone who tried to help.
Some cars are just born evil. And I got one of 'em.
This is a major defeat for me. I've been able to tame the worst of British Leyland. I never thought a GM product could be worse.

Rich Truett
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Gall757
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Report this Post04-29-2015 09:26 PM Click Here to See the Profile for Gall757Send a Private Message to Gall757Edit/Delete MessageReply w/QuoteDirect Link to This Post
well....OK.

You have been at this about 60 days?
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Rich Truett
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Report this Post04-29-2015 09:31 PM Click Here to See the Profile for Rich TruettClick Here to Email Rich TruettSend a Private Message to Rich TruettEdit/Delete MessageReply w/QuoteDirect Link to This Post
I have had the car since January.
Since then, every sensor on the engine has been replaced.
And the coil.
It's a nice car; works well except for that damn idle problem.

I think it is a heat-sink situation.
Something is getting hot and failing.
I tried an additional ground on the engine tonight.
I can't think of anything else to try to fix.

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Report this Post04-29-2015 09:42 PM Click Here to See the Profile for YannskyClick Here to Email YannskySend a Private Message to YannskyEdit/Delete MessageReply w/QuoteDirect Link to This Post
Hi Rick


I had the same issue and probably you'll checked it but it was the arm on the throtle b who connected to the tps it was loose. With my finger i can played with it and changed the rpm. Remove the tps and you will find a flat screw thight it with the arm at the highest position. Look for the output volt from tps and should be around 0.5 v. The tps must be adjustable honestly i never find how on the v6. I presume this screw on the tb is there for that purpose but not sure?

Checked it out it's free

Yannsky
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Rich Truett
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Report this Post04-29-2015 09:57 PM Click Here to See the Profile for Rich TruettClick Here to Email Rich TruettSend a Private Message to Rich TruettEdit/Delete MessageReply w/QuoteDirect Link to This Post
Thank you.
I will try that tomorrow.
I did wiggle the TPS, the wiring, and it does change the idle speed.
So, I think the problem is in that area.

Rich
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Report this Post04-30-2015 12:11 AM Click Here to See the Profile for fierogt28Click Here to Email fierogt28Send a Private Message to fierogt28Edit/Delete MessageReply w/QuoteDirect Link to This Post
Rich, don't give up...you've done to much so far it ain't time to quit.

Maybe trace those 3 wires at the TPS, and maybe you can splice a new pigtail.

Since you have a new TPS, which I suggest you get an AC Delco.

Let us know what you find.

------------------
fierogt28

88 GT, Loaded, 5-speed.
88 GT, 5-speed. Beechwood interior, All original.

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Gall757
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Report this Post06-06-2015 05:36 PM Click Here to See the Profile for Gall757Send a Private Message to Gall757Edit/Delete MessageReply w/QuoteDirect Link to This Post
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