Stock foxbody efi setup. Sometimes while running perfectly, rpm will hang at around 2k and not go lower than that until I turn off key. Restart returns everything to normal. I have a bit of blowby and wondering if a oiled up 02 sensor could be the cause. I’ve done the usual base idle setup, checked tps, iac etc.
I had a similar condition on several occasions with my 1989 GT. Mine was always related to the 10-pin connectors (aka salt and pepper shakers). Next time the idle is hanging, try moving the 10-pin connectors around to see if the engine idle changes. If so, look up 10-pin connector fix.
Dean is right, I've had this happen a bunch on my '89. You won't notice it cruising down the road, but get to a stoplight and the idle just haaaaaaaangs...
What's happening (from the Quarterhorse logs) is that the TPS signal drops out and the EEC thinks the new idle TPS setting is 0V. Then when it connects again, the EEC doesn't think it's at closed throttle, and pumps up the IAC.
I'd love to find a permanent replacement for the stock connectors. I'd even go with GM parts
Thanks for the suggestions. I’m on my 3rd iac and tps, and serviced my 10 pins last year. Servicing the 10 pins did solve some other issues I was having. About the TB butterfly....do you mean like a physical hanging of the valve? I wouldn’t think that would be the issue as a restart clears the problem. Gotta be sensor/electrical/eec related.
Next time it does it I will pull over and start jiggling stuff. Will jiggle stuff on the engine too ;j
Happened again. Jiggled the 10 pins, no change. Unplugged IAC and idle dropped to normal. Plugged back in idle jumped again. This is a nearly new Motorcraft IAC on it.
To add to this, I have seen a corroded positive battery cable cause this as well. It always seemed to happen after an instant heavy load was put on the battery such as the fan turning on.
Thanks for the replies. Thought I had it licked, but it happened again tonight. Regarding voltage....might be onto something there. Ever since I did this conversion I have had flickering headlights when at idle. I’ve tried raising idle, but that causes TPS issues. I’m running a 3G alt and have no charging problems and battery voltage is normal. What would be a good way to eliminate this as a cause?
With the help from this great resource of talent and experience, I’ll get this sorted. Thanks guys.
edit: I should mention the battery is in the trunk and I’m using the stock 2awg wire from the trunk to the engine bay.
Where should I be checking voltages at to find the cause of the flickering headlights. Battery reads normal with engine off ,and running. 12.6 key off, 14.6 to 14.7 engine idling. Measured at the battery posts. Stock fox 5.0 efi (sn95 front drive) with 3G alt added.
Checked voltages at different areas of the car tonight. Getting strong DC voltage at the lights and other accessories. BUT, I did a little internet university and discovered that a bad alternator could be putting out small amounts of AC. When that happens the result is flickering lights. I checked for AC with a DVM and got fluctuating readings of .1 to .3 v. I could see where something like this could possibly make the eec grumpy.
I’ll throw on a new alt tomorrow night.
Changed the alt. Flickering eliminated. Yay.
Went out for a spin, came home and noticed a layer of coolant below the oil in my catch can. Bummer. I guess my mysterious bubbling coolant issue is soon to be solved. Hoping it is only head gasket and not a bad block.
Thanks for the help everyone, especially Indy. I like your style- no coddling or small talk, straight to the point.
While I agree with you on trying to measure, rather than take a shot with a shotgun, this rarely happens when you are at home, in the garage and you have the leisure of back probing connectors.
It invariably happens on the road and it is rarely convenient or safe to pull over and start diagnosing.
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