[Lightfoot]

My '89 LeSabre (3800) has had a Low/No Idle syndrom re-surface, and seems to mostly occur on cold starts in heavy humidity. But: also it has happened multiple times when the gas tank has been filled to the brim, then driven less than 40 miles & allowed to cool all the way down. Makes me wonder if the EVAP cannister/solinoid is the culprit.

Once warmed up to operating temp, the engine runs fine, although the idle speed has always seemed a bit too low.
Monday morning Oct 15, it didn't want to idle even after I had warmed the engine past normal temp. Then after I had shut the engine off for about 15 minutes, it did stay running without my foot on the accelerator.
SES light never came on during any of these recent episodes, but my scanner reported TPS voltage too high, don't remember the code. I fashioned a probe out of a paperclip to stick through the foam plug in the back of the connector. Filed it nice and sharp and it worked quite well. My reading with the engine OFF and throttle closed was .421-.428 volts. GM service manual calls for .33 to .46 volts, so it is apparently adjusted correct.
It increased proportionaly when I moved the throttle lever. I didn't try it with the engine running.

I'm wondering if the Idle Air Control valve or EGR could be what is actualy malfunctioning and somehow 'fooling' the ECM into thinking the TPS voltage is too high or low when the problem arises.
A couple of times the engine has idled normaly at cold start; then suddenly died after 90-120 seconds of 'warm-up idle' without me ever touching the throttle. Then after I give it a few seconds to rest, it will run well enough to get it out into the road and progress up to speed. Once this engine has been driven a few miles, it seems to have no issues until it cools back down to ambient temp. Although the normal idle is too low for my liking.

Appreciate all thoughtful suggestions.

[Lightfoot]

Also, is there a simple way to check if the EGR valve is stuck open when it isn't supposed to be?

Is there a OBD I code for the IAC valve? I can't seem to find it in my service manual.
It mentions code 44 "may be set" if IAC is disconnected.

[Lightfoot]

Is there an OBD I code for this if it fails?
I'm beginning to suspect that it, or the cannister itself is causing my No/Idle issue when the gas tank has been squeezed full. Even though I have NEVER had a similar problem with any of my other four '88-'90 3800 powered cars (over 150K combined miles).

I had no symptoms yesterday when cold starting the car in 50-55 degree weather after a night of HEAVY dew. Last Monday, the moisture was very much the same, but the temp was above 60, and I had severe issue keeping the engine running.
I had just (squeeze) filled the tank the previous night and only driven 34 miles.
In at least three other episodes, it was the first cold start after filling my tank and driving less than 40 miles.

I think the TPS codes (21-22) could be a red herring by-product of the poor idling episodes.
I am going to try another cold start tommorow, as it is supposed to go down into the mid-30s tonight.

[salem1912]

"But: also it has happened multiple times when the gas tank has been filled to the brim, "
Why do you fill it to the brim?

[Lightfoot]

Originally Posted by salem1912

"But: also it has happened multiple times when the gas tank has been filled to the brim, "
Why do you fill it to the brim?

Old habits die hard.
I sarted doing that over 25 years ago to calculate fuel mileage as accurate as possible. This is not to say I fill it right to the top of the filler neck, it's just a figure of speech.
On rare occasions with a 'soft pump' I have had the gas come running out the filler neck very unintentionally, and I hate it when that happens.
But much more often is the case where a pump will kick off prematurely, and I only discover this when the gas gauge moves below F much sooner than normal.
In case you're wondering, I only pump my gas with the lever at about half speed.
After the initial shut-off, I nurse .75 to 1.5 additional gallons in, depending on how a pump "feels".

I'm going to repeat myself here and say I've NEVER had any reprocussions from stuffing my fuel tank, and this current mallody may not have anything to do with it either.

[salem1912]

Reason for not doing that is your evap canister may be filling up with raw gas. It is only intended to draw vapors,which on a restart(normally cold restart) is sucked back into the intake to help run better. Once a canister is filled with raw gas it hard to recover to it's normal state(vapors). Don't know if this is the problem in your case? Good Luck Tom