Idle bogging under load?

[BestDinosaur]

93 ATX: Cars idle always bogged down to around 500 rpm and bounced back up to 700ish when coming to a complete stop or being revved while parked. After changing alternator and fuel pump problem went away for a about a month, then came back with a vengeance.

Car bogs but never stalls when coming to a stop while driving, but if I rev it more then once while parked it will bog badly then stall and not turn over unless I let it sit for a few minutes. I'm lost as to what could be causing this, the battery, alternator, and fuel pump are all new. All the censors are new accept the DIS. Could it be my coil is on its way out? Or is my idle just set too low?

 

[SHOZ123]

Dirty or lazy IAC valve. You can try cleaning it or adjusting the throttle stop. Then relearning idle.

 

[rubydist]

do not adjust throttle stop!

fix the iac problem.

 

[SHOZ123]

This is the way to do such taboo procedures as adjusting the throttle stop.

On a hot motor adjust stop screw in so the car is idling around 1500 rpm.

Disconnect IAC

Turn idle down to 450 rpm.

Turn off car and disconnect battery.

Reconnect IAC and start car.

Go through idle learning procedure.

 

[rubydist]

^ This is correct, however it will not fix the op's surging idle issue. he needs to fix or replace the iac for that.

 

[SHOZ123]

It seems the IAC is not so much surging as struggling to regain control of the speced idle rpm.

By opening the throttle enough so the engine will idle on it's own, abet at at below normal rpm, this will give the IAC more head room and it will work more efficiently. Assuming the IAC works.

 

[BestDinosaur]

Ill check the IAC and see if its clean before I mess with the idle.

 

[silverbullet92]

For those who are green, What is the IAC's function per say?

 

[intimdatr]

Intake air control at idle. It allows air into the intake to allow the car to idle.

 

[silverbullet92]

Thank you for that. I just didnt know what it stood for but makes sense. Is it just a diaphragm?

 

[msteiny]

In a round-a-bout sort-a way it is. Its not a rubber diaphram if that what you thinking.

This is the definition from the book.

Idle Speed Control (lSC) Valve
The Idle Speed Control (ISC) Valve assembly is an electro-mechanical device controlled by the EEC-IV processor. It incorporates a linear actuator which positions a variable area metering valve. In response to commands from the EEC-IV processor the air bypass valve controls airflow at both warm and cold idle.

Have you tried an idle reset? Is your MAF clean? Bad Gas/Fuel filter? Temp sending unit going bad? Oil in plug wells?

I can keep going but this would be a good start.
Keep us posted.