A few more idle issues

[mts3]

93 PGT MTX, I couldn't find anything exactly like this mode of operation:

When cold starting, the car doesn't do fast idle.

TPS set, TB cleaned, IAC cleaned, hot idle 650-700rpms, timing 10 deg BTDC @ idle (per the instructions)

At hot idle, there is about a 50 rpm constant fluctuation in the idle. It just isn't smooth. It's barely detectable on the tach, but very detectable by the ear.

Once letting off the gas and putting in neutral, the engine speed goes down to ~1200, rests, goes to 800, rests, then goes to normal idle and stays there.

Any thoughts? The car is perfectly driveable as it is, but I'd like to get these issues out of the way.

The only code being thrown is a 16, EGR. Would that cause my problem? Removing the EGR does NOT sound like fun but I guess it has to be done.

[KevinD]

If the EGR valve is leaking, that will affect your idle, but you should still get a fast idle when cold. Have you tested the BPA (Bypass Air) control (part of the IAC assembly)?
KevinD

[mts3]

When I removed the TB and cleaned it, the only parts I checked were the continuity on the TPS with the two feeler gauge thicknesses. I also checked for action at that black solenoid when I applied 12v.

How do I test the BPA part of the valve?

Thanks
Tyson

[KevinD]

From the Service Manual:
"The Idle Air Control Bypass Air (IAC BPA) valve consists of the Bypass Air (BPA) valve and the Idle Air Control (IAC) valve.

The air valve functions only during cold engine operation to increase engine idle speed. The BPA valve consists of a thermowax bead and the valve.

Engine coolant is directed around the thermowax, which opens and closes the valve. During cold engine operation (below 60°C [140°F]) the thermowax is contracted enough to allow the air valve to open. As the engine coolant directed around the thermowax heats, the thermowax begins to expand. When the engine coolant reaches temperatures above 60°C (140°F), the thermowax expands and closes the air valve."
As far as diagnosis, you take it apart, and inspect & clean it. You could immerse the BPA in hot water & make sure it works properly.
KevinD

[mts3]

Thanks. So is the BPA in the part that comes off using the 4 #3 Phillips screws?

Tyson

[mts3]

Okay so I got the IAC separated again. I am including a link to it. On the left side, there is a part with a spring (the IAC solenoid part?) On the right, there is a red thing down in the hole that the coolant goes in. Where do I need to be checking for this BPA operation?

Thanks

http://myweb.cableone.net/dsherman/iac.jpg

[mts3]

Any takers? A search yielded nothing but this post, one telling someone to search for "clean BPA", and one other which didn't say anything either.