Intermittent drop in idle speed. No check engine light on.

[99Vortec]

 

[99Vortec]

Can I use carb spray or equivalent to check for wear at the throttle shaft bushings?

What I mean is, will potential wear at this location manifest as a vacuum leak?

I'm fairly sure it's likely a worn distributor, the plug wires, or the throttle shaft bushings.

(Distributor show's about 4-5 degrees of variation.)

Just jacked my back up a bit the other day and haven't had time to investigate further.

Luckily, a bit of Ale is helping to alleviate the pain.

Merry Christmas!

 

[SunlitComet]

Yes. Sort of. Half of that shaft is exposed to the plenum and the other half to the atmosphere. It is harder to tell if it leaks thru a gap on the upper half if that is the only place it will leak. Of course vaporization of the fluid could reach the bleed hole on the throttle plate and cause a momentary surging effect.

 

[99Vortec]

So I replaced the plug wires, and the idle problem smoothed out.

Also checked the throttle shaft for deflection and it seemed minimal to me. (Like 1/32")

Pretty sure it will smooth out even more with a new distributor. (But hey, if it is not broken do not fix it.)

One of these days, when I am not so ****ing lazy, I'll have to record a fraps of the timing variation. (@Idle of course.)

Anyways, thank you very much you two.

*edit* Vortec's are sweet at 5,000 RPM!

 

[ccapehartusarmyINF.(ret)]

usually when i see stuff like that i pay attention to voltage output guage
plus turning yer wheeels like that sitting still can be a bit of a load

 

[SunlitComet]

Would like to add the when you turn lock to lock the pump load that bogs down the engine does cause the puter to bump open the IAC valve in attempt to reestablish the the desired minimum engine speed. Hence an engine surge.

 

[99Vortec]

Would like to add the when you turn lock to lock the pump load that bogs down the engine does cause the puter to bump open the IAC valve in attempt to reestablish the the desired minimum engine speed. Hence an engine surge.

Yes, that's what initially threw me. The IAC was the very first thing I checked and it checked out ok.

Was a bit reluctant to throw parts at it. (Wires in this case.) But it did do the trick.

 

[OR VietVet]

I have taken IAC valves out before, be very careful of the gasket, it could crack on you. Took IAC valve and sprayed down with carb and brake cleaner to free up a gummy actuator. The carbon builds up and can be slow to react to a load condition. Has worked for me. Once installed may have to let it relearn the idle/load circuit.

 

[99Vortec]

I'd like to get this.....http://www.rockauto.com/catalog/moreinfo.php?pk=86747&cc=1355510

(Even though the throttle deflection is minimal.)

Expensive though! Like $345.00

And a new distributor...

http://www.rockauto.com/catalog/moreinfo.php?pk=4048398&cc=1355510



Compression is within about 4-5% on this engine.

So much for throwing parts at it. Hehe.


The IAC looked to be like a basic valve/seat type of assembly. (Only electronically controlled.)

Valves and seats do wear...

---------- Post added at 09:56 PM ---------- Previous post was at 09:34 PM ----------

usually when i see stuff like that i pay attention to voltage output guage
plus turning yer wheeels like that sitting still can be a bit of a load

These OBDII gauges look nice...


http://www.aeroforcetech.com/

 

[SunlitComet]

I would leave the throttle body alone for now but replace a valve if needed.