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1990 talon stalls randomly and I'm stumped.

boosted99_420

10+ Year Contributor
308
1
Apr 26, 2010
Fort Carson, Colorado
As title says my 1990 Talon stalls randomly at stop lights and stop signs. I just put a new Alternator on it and thought that was why but it wasn't. It still runs and drives great. But one thing is there are quite a bit of components drawing energy. IE: acvr, big ole tach, an oil pressure have that dont work except light, wideband, boost gauge light, and aftermarket radio. I got the 90and alt so its not that its the wrong one. Any info is needed and welcome.
 

steve

DSM Wiseman
14,715
1,587
Feb 3, 2002
Boulder, Colorado
This could be as simple as a vacuum leak or a Idle Position Switch (IPS) that isn't grounded, or a misadjusted Basic Idle Speed Screw (BISS) but there is nothing to go on in your post.

What was the reason you put the alternator in? Dropping voltage, no voltage?

When the car does idle, what speed does it idle at?
Does it idle up when you push the AC switch?
Does the idle drop when you turn the steering wheel when stopped and idling or keep the same?

Is the BOV recirculated?

These are just the basic starting questions.

The idle speed normally controlled by the ECU. When it sees the IPS close it takes control of the engine speed to keep the car from stalling. The basic throttle bypass air is adjusted by the BISS and the Fast Idle Air Valve (FIAV) in the throttle body. The ECU adds or subtracts air using the Idle Speed Control (ISC) attached to the throttle body. The ISC coils go bad and if they short out, blow the drivers in the ECU. The IPS requires a good ground between the switch and the battery. The ground connections often get removed over time and then the ECU doesn't know that the throttle is closed. People remove the FIAV because they start having fast idle problems and rather than fix the cause they just remove it and block off the air passages. The capacitors in the ECU leak and destroy critical circuit traces. These are just the start of potential issues that could be causing what you describe.
 

boosted99_420

10+ Year Contributor
308
1
Apr 26, 2010
Fort Carson, Colorado
Ok found out exact when It dies. It stallls when the radiator fan comes on while stopped. Now to figure out why
 

steve

DSM Wiseman
14,715
1,587
Feb 3, 2002
Boulder, Colorado
Ok found out exact when It dies. It stallls when the radiator fan comes on while stopped. Now to figure out why

I've seen that happen for two reasons. If you have an open air filter (no more air box) the hot air off the radiator causes the idle to drop. The current draw when the fan engages causes the alternator to work harder and the idle drops.

In both cases the ECU and ISC are supposed to raise the idle up to adjust.

Until you answer the earlier questions I can't help much.
 
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