CIS-E car surging for idle.

[16v Jason <jason@scirocco.org>]

Hey all,
	This doesn't exactly concern my Scirocco, but my Mercedes has the same 
CIS-E fuel injection, and I've spent about $1000 so far to try to get it 
running right-- and still without luck.  I'm at the end of the rope 
financially, so I thought maybe you could help. :)

	The car in question is a Euro model '88 190e with a 2.0 8V.  It has CIS-E 
without a knock sensor, but with the addition of a Mercedes Over-Protection 
circuit that monitors idle to make sure it's even and smooth.  It has about 
83k miles on it.  This problem started mid-January following an oil change 
at Wal*Mart, and has continued, though it usually gets worse the higher the 
ambient air temperature.  Since the temps have been getting warmer, it's 
gotten to the point that it needs to be taken care of.  This past winter 
was the first winter the car has seen since it's new, so I was expecting 
some problems...

	The symptoms are as follows:  At idle in Neutral, the engine surges to 
maintain idle, from about 500rpm to 1200rpm and back.  It does stall 
occasionally, though not since all the work I've done so far.  Symptoms 
become worse as the engine heats up, but it will sometimes do the same when 
cold.  Under low-rpm/high load conditions within about 2 minutes after 
start (warm or cold), the engine will suddenly have no power.  There is no 
change in engine note or smoothness, it just feels like something lopped 
off 30hp.  Then, as quickly as it came, it will snap back into Normal mode 
and continue.  It'll do this a few times until it's warm.

	With the idle stabilizer circuit disconnected, the car idles without 
surging, but either at 1200rpm or 600rpm, depending on whether it's warm or 
cold.  Normal idle for the car is about 750rpm.

	Typically, the Over-Protection Relay goes on these cars, and causes 
similar problems.  Mine was original, which is unheard of, so I replaced 
it.  No change.  Next off was a new O2 sensor (for $200!).  No change.

	I've checked everywhere for vacuum leaks, and haven't been able to find 
any.  The engine doesn't react to spraying Starting Fluid at (or near) the 
throttle body intake, so obviously it didn't do anything spraying it on any 
vacuum lines.

	I changed the Spark Plugs.  No change.  I disassembled, cleaned, and 
re-fitted the distributor.  No change.  I checked the plug wires using the 
water-spray technique and saw a little arcing, but not all that much.  I 
cleaned all of the electrical connectors in the engine compartment-- some 
of which were so grease and oil-soaked that it's a wonder the car runs.  No 
change.  I took out the idle stabilizer valve, cleaned and lubricated it.. 
(although it was squeaky clean in there anyway).  No change.

	Then, I took it to a MB "specialist" in the area.  He did a compression 
check.  Passed.  He did a fuel pressure check.  Passed.  He checked the ISV 
for function.  Passed.

	There used to be about a 2-second delay before the injectors would turn 
completely off after releasing throttle over 1200rpm, but now I don't feel 
that anymore.  So, I unplugged the switch.  No change.  I jumpered the 
contacts on the lead to the switch.  No change.

	So, in short, everything looks OK on the entire fucking fuel injection 
system, but the problem persists.  The only thing I haven't done is check 
any of the Differential Pressure Regulator currents, which I guess is my 
last resort.  The car does run a little rich (judging from carbon deposits 
on the plugs), but normally otherwise.

	Does anyone have any other suggestions on what it could be before I bring 
it back to the shop and wipe out the rest of my life savings trying to 
diagnose this??

TIA,
Jason




----------
1987 Scirocco 16v
1989 Mercedes 190E Sport Euro


http://members.aol.com/rocco16v  


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