[s-cars] 93' S4 - Hard Starting

[Djdawson2 at aol.com]

In a message dated 1/11/2005 4:45:49 PM Mountain Standard Time, 
james.murray at ericsson.com writes:

> So... I went down to my favorite Denver area Mechanic/tuner, Champagne 
> Motors, and had them pull codes.  

Sorry to hear that... you need a new favorite.

Code for the Throttle. Pos. Sensor came up.  Hmmm.  We cleared that code with 

> the hope that it would come back after a few motor starts, stops and 
> driving.  It did not.  TPS code makes no sense to me since we know that you can 
> disconnect the TPS and the car will start without it!

Likely not the issue.  TPS failures seem to come in 2 flavors... either the 
idle switch goes bad, or the potentiometer goes bad in the form of an open 
circuit somewhere past 1/2 throttle.  The latter doesn't seem to hurt operation at 
all, and neither causes starting problems.  

> 
> 
> My initial thought, based upon years of soaking up all of this great list
> wisdom was a bad Cam Position Sensor.  But doesn't a bad/flaky CPS usually
> set a code in the computer??  Also, the CPS is a bear to get to and is an
> expensive part - so hate to go blindly replacing this thing.

I wouldn't jump to that conclusion without first checking the sensors on the 
bellhousing... TDC and engine speed sensors.  Easy to get at, and easy to 
check.

> 
> Champagne's thought was that this behavior might be due to a
> bad/intermittent fuel pump check valve.  But, this only makes sense if after
> a long rest (cold motor) e.g. - that you would need to crank for a long time
> to get fuel back into the system.  This AM, after a long cold night's rest,
> the car started right up!  That shoots the bad check valve theory, right?

Likely it does.  The system should hold pressure.  The only easy way to check 
that is to crack a fuel line slightly and check for pressure.

I would test and clean the tips on the speed and TDC sensors, and see if the 
behavior changes.
HTH,
Dave in CO