[Shotimes] Idle Changes when Depressing Clutch Pedal

[Leigh Smith]

Tim;
My 248k mile 89 Titanium developed similar issues. See if the idle speed 
settles down differently with the AC on or AC off. Mine was related to 
the AC compressor beginning to disintegrate,unknown to me at the time. 
(At 180-220k) The extra drag was screwing up the idle learning memory & 
programming, but it acted normal with the AC off. I chased that one for 
a long time til the compressor blew. A new one fixed the idle problem. I 
also remember the clutch seemed to have some effect on it. In theory you 
should be able to measure the rotational drag on the compressor, but I 
never got that far. Lasted for a year or two that way.

On the spark knock, how old is the fuel pump? There is a knock sensor, 
it is buried in the vee under the fuel rail.

You could pull the octane shorting plug in the wire harness under the 
driver side rad hose inlet, near the cruise control, and see what effect 
it has. Retards the timing about 10 degrees. But knock sensor does about 
the same thing. If you run premium, you should never hit the knock 
sensor, if the car is stock, and OK. Pulling the plug will let you feel 
what it runs like with the timing retarded. Do it once, and you'll know 
if you ever trip the knock sensor on the street.

If it is lean due to a weak fuel pump that may not help enough. 
2000-3500 is where the factory calibration is leanest and spark or fuel 
problems arise first. My weak fuel pump did just that, but at 1/2 
throttle. Especially when 1/2 warmed up, it was almost undriveable til 
warm. Check the fuel pressure.

Leigh

T Waters wrote:
> Folks,
> It has been years since I was on the SHO list, but I have run into a 
> very interesting problem with my '89.  It has begun to idle higher that 
> normal (1500 rpm) and takes longer to settle down to normal idle (800 
> rpm) when coming to a complete stop, engine warm or cold.  It has a new 
> IAC valve and TPS.  Another oddity is that when I depress the clutch 
> pedal, it idles back down to 800 rpm - like taking it out of gear when 
> coming to a stop.  This is very repeatable and there is no CE light at all.
> 
> Another problem is that I have spark knock, when engine warm, from 2000 
> to 3500 rpm under WOT or slightly less than WOT.  I have had the engine 
> decarbonized at FPS in ATL recently to try to correct the problem, but 
> that has not.  Could it be the knock sensor?  Is there a knock sensor?
> 
> Any help with these two problems would be greatly appreciated!
> 
> Best regards,
> Tim Waters
> 89' Lt. Titanium
> 
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