1996 SL ENGINE RACING PROBLEM

My '96 SL single cam has 185K on the clock, and has been running fine.
A few weeks ago I changed the oil and hosed off the motor with a
garden hose. Then the "Service Engine" light came on, but it was
running fine. A few days later it went off, and my buddy at work
hooked up his code readed and said it had a EGR related code in the
memory.
I drove it a couple of weeks, and light stayed off. It wouldn't start
the other day, and wiggling the battery terminals got it to start, so
I drove it home and cleaned the terminals, which really didn't look
bad at all, but I polished them bright with a wire wheel.

The next time I drove it after the terminal cleaning, the engine had a
high idle, and would race up to 3000 RPM when I would clutch it
between gears. the idle would eventully settle down to 750 RPM.
Drove it to work today, and it still would race up between gears,
almost like I wasn't letting off the gas pedal when shifting. When I
would put it in neutral coasting up to a stop, the engine would be at
2000 RPM, then slowly drop to a 750 RPM idle. No check engine light
is coming on at this time.

What could be causing this?

 

Why the hell did you do that???

Do you think you might have sprayed water on some electronics that weren't
supposed to get water sprayed on them?

Hosing off the motor with a garden hose.

 

Let's go with the EGR valve possibly sticking open. Any gross vacuum leak,
including excess EGR flow, will cause the RPMs to kick up.

The fact that you had a loose battery cable probably lost some of the
adaptive settings in the ECU. This is re-learned as you drive (the 'drive
cycle') and may correct any problems after 50-100 miles.
EGR related codes (most codes for that matter) are not set in memory until
the engine is at normal operating temperature...coolant level, thermostat
and coolant temperature sensor (CTS) are responsible for this. For that
matter, an open CTS circuit often causes high idle and rich fuel mix. Check
that the CTS cable is not pinched or loose at the sensor. I've seen worn
motor mounts that allow the engine to twist and put tension on loose
harnesses.

 

I have always changed my own oil on this SL since it was new.
When you pull the oil filter, oil runs all down the back of the block,
rubber suspension/ steering boots, and the frame. I always pour a
bucket of soapy water on that area, and hose it off with a garden
hose. It's not high pressure, so I'm not really getting it any
"wetter" than driving in a rain storm, I figger.

 

Thanks, this is most helpful! The car actually passed emissions
testing today, and I'll probably plan on replacing the EGR valve soon.

 

I always said that before they make a guy (person) a design engineer, they
should have 'em work as a tech for at least 6 months. Much to be said for
the European apprenticeship programs.

Never understood why most oil filters are horizontal and have the problem
you detailed...

Couple of suggestions
1. punch a hole in the old filter and let the oil drain out of the hole
before you remove the filter. Hole should be at the lowest point of the
filter. Do not punch deeper than about 1/4" to avoid going through the
filter element.

2. get a filter re-location kit. Space is pretty tight these days in engine
compartments but it may work. These are available from speed shops and jc
whitney (last I knew). Allows you to mount the filter vertically.

 

Yeah, I had that happen. When I stopped at a traffic light, the rpms
would be 2k to 3k before dropping down to idle speed after 30 to 40
seconds. The accelerator pedal and cable were fine. The 'service
engine soon' light did not come on. I thought the throttle body might
be gummed and sticking so I removed it but it was actually fairly clean.
I cleaned it up anyway and reinstalled it but the problem didn't
change. But...the throttle body had a little solenoid valve and piston
attached to it that opened and closed a little bypass hole around the
throttle body butterfly valve. Turns out that is the 'idle air control
valve' (IAC) that opens to allow the flow of air through a little hole
about 1/4" in diameter that provides the air to the engine for idling
when the throttle butterfly is closed. I didn't think it could be bad
because there was no fault code or SES light but I decided to change it
as there wasn't much else that could be causing the problem. Et voila!
The problem was solved. I got the new one for $50 at car quest. It
only took about 15 minutes to change on my '92 SL2 (221K on the clock now).