Engine REV's between shifts,Why?? - PeachParts Mercedes-Benz Forum

Paratroop · #1 05-23-2009, 08:36 PM

1986 560sl.From park to reverse it revs up 200.From reverse to drive,same thing.From whatever gear to whatever other gear it
revs up 200 RPM and then shifts.What causes this,and why doesn't
it just stay the same thru the shifts??It is primarily worse on cold starts(after
it sits 4 or 5 hrs.After it is really warm it is not as bad,but it still does it!

cclake · #2 05-24-2009, 07:31 PM

I sure would like to know if you find the problem. I have been fighting this problem for two years. I have cleaned the idle control valve, replaced the i nector seals, replaced more vacuum lines than I can count. Next will be to replace the oil temp sender. Mine does come down to normal 800 rpm after about 10 seconds I hope you have better luck.

Paratroop · #3 05-25-2009, 07:49 AM

If I find the answer you will be the 1st to know.

Tims450SL · #4 05-26-2009, 12:40 AM

Has anyone changed the trans filter- and had the tourque converter drained? That is the proper mercedes technic there is a bolt in the middle of the tourque converter- and when you drop the pan and remove the fileter- you can turn the converter until the hex nut appears. drain it completely- then remember to run the car as you replace the fluid- I think it takes about 7 quarts just to fill the TC. Don't quote me on that- good luck- that always has rectified the problem for me. (done it 3 times 3 diff SL's) Thought the trans was bad- per the idiots at aamco and other trans rip off artists.

Paratroop · #5 05-26-2009, 07:29 AM

Yes,TC drained,new filter installed and modulator valve.

TylerH860 · #6 05-26-2009, 01:54 PM

We're only talking about 200 rpms here, correct?

The engine is not under load when you have it out of gear, making it idle slightly higher than when in drive or reverse. What is the idle in park and in drive? If its within 200 rpms than it should be fine.

Now, if you're driving and the car revs between normal shifting, that is called flaring. Sometimes its only a modulator adjustment, but can also be a major tranny issue.

Paratroop · #7 05-26-2009, 07:09 PM

It shifts fine when driving,Cold starts,From P to R it REVS 200 and up and
makes for a harsher shift into Reverse.From R to D it is not bad.I have replace flex discs,motor mounts,subframe mounts,shocks,Diff mount,have
checked vacumn hoses till I see them in my dreams,I think the only thing
I haven't replaced is the temp sender on the Passenger side head,OVP replaced,Cleaned ICV,I wonder about the air intake disc??

TylerH860 · #8 05-26-2009, 08:55 PM

sounds completely normal to me. When cold, the car is idling higher and feels more forceful. These are powerful cars, so you're going to feel it. My sl is the same, so is my 6.9, my dads vintage trans ams, etc.

I'm curious what your idle is at right now. Itshould be at about 600 in gear and around 800 out of gear. When cold, a bit higher

Paratroop · #9 05-26-2009, 10:35 PM

Maybe I should ask another question,Do All 380's,560's.act like this and
if they do then they must all have a harsh shift into REV and Drive.Yes or No??

TylerH860 · #10 05-26-2009, 11:09 PM

If your car is idling higher than normal, then it will feel harsh. That's why I asked what your idle RPM is.

If you have a vacuum leak and its idling at 1100 rpm, then its going to feel really harsh.

sublettd · #11 05-27-2009, 11:22 PM

If the Idle Speed Control Unit and slide valve are working correctly your engine RPM should increase ~200RPM when shifting into neutral or park.

Looks like you have changed a lot of things which have little to do with the fuel system. Having just completed a complete engine rebuild on my 500SL, one thing I learned is there are many variables that affect the idle and RPMs. Sounds to me like you might have a problem with the fuel system pressure.

On the back left side of the fuel distributor there is--for want of a better term--a needle valve that screws into the housing and controls the fuel system pressure. Pressure is raised and lowered by adding or reducing the number of shims. To check this you really need a good technician who has the appropriate guages and understands how the system operates.

My SL has a Warm-UP Regulator, which I don't believe yours has. My mechanic adjusted the number of shims to increase the system pressure and then made an adjustment to the WUR.

The air intake disc will obviously affect the amount of air that gets into the system. My engine backfired a couple years ago and the backfire actually bent my disc a very miniscule amount. However, it was just enough to allow too much air at low idle, which caused it to idle rough. The bar across the top of the air intake is to prevent damage to the disc when/if the engine backfires. Guess it doesn't always work as designed.

The disc should be flat and should be perfectly centered. It should also sit in the middle of the ridge on the bottom of the housing. The height is adjusted by a detente under where the fuel line comes into the LF of the FD. Unfortunately, you have to remove the FD in order to be able to make the adjustment.

Anyway, recommend you have the system fuel pressure checked before tossing more money at more parts.

Quote:

Originally Posted by Paratroop

It shifts fine when driving,Cold starts,From P to R it REVS 200 and up and
makes for a harsher shift into Reverse.From R to D it is not bad.I have replace flex discs,motor mounts,subframe mounts,shocks,Diff mount,have
checked vacumn hoses till I see them in my dreams,I think the only thing
I haven't replaced is the temp sender on the Passenger side head,OVP replaced,Cleaned ICV,I wonder about the air intake disc??

sublettd · #12 05-27-2009, 11:24 PM

No, they all don't shift harshly at all. Mine shifts smooth as silk.

Quote:

Originally Posted by Paratroop

Maybe I should ask another question,Do All 380's,560's.act like this and
if they do then they must all have a harsh shift into REV and Drive.Yes or No??

Paratroop · #13 05-28-2009, 08:20 PM

Cold Start 800.After it gets warm,750.As soon as you just barely move it
off park 950 till it shifts into reverse,which causes a harsher shift.From REV you move it barely off REV into D 950 into drive.
This morning I did another cold start observation.I pulled the vacumn
line off the Ignition Module and did a cold start.700RPM moved it just off
Park,well HELL it stayed right there at 700.No rev nothing.Smooth shift.
So maybe like Chuck Taylor said the Ignition module is not sensing the shift to retard the timing and keeping it at a higher rpm.Any Thoughts on
that????