need help with Idle dropping when in gear

[kamotezee]

 i have 280 sl. The problem is every time I shift gear in drive or reverse the idle drops to 400 rpm, sometimes the engine stops. When in park or neutral the idle is 800rpm. It runs ok. need help or any recommendation please.... thanks in advance

[Jonny B]

This is a car with an automatic transmission? A/C? There are a number of threads on the forum about this. I recommend you use the search function to look for information. There is a solenoid that moves the linkage when the car is put into gear (or when the A/C is turned on) to keep the revs up. I believe it is not on the later cars, but not sure.

[Shvegel]

Also search for "3 position solenoid". Accessible though a plate on the right of the trans tunnel under the carpet this solenoid adjust the control pressure of the transmission at idle to reduce the drag.

[kamotezee]

This is a car with an automatic transmission? A/C? There are a number of threads on the forum about this. I recommend you use the search function to look for information. There is a solenoid that moves the linkage when the car is put into gear (or when the A/C is turned on) to keep the revs up. I believe it is not on the later cars, but not sure.

yes sir. my car has automatic transmission and A/C. but there no solenoid in the intake manifold that push when ever i turn on the a/c or shift the gear. i guess that solenoid remove by previous owner. thanks

[Travis71280]

I'm having the same issues with mine. I also have A/C and an automatic transmission, but the constant speed solenoid was only rigged up for the A/C, not the transmission. So is it primarily the three position solenoid that keeps the car from stalling then or is there more to it?

[Shvegel]

Everything you need to know is here:

http://www.sl113.org/forums/index.php?topic=10814.0

A stuck linkage or a miss-adjusted or dirty throttle switch are the usual culprits followed by someone messing with the connections at the terminal block under the car. It's a simple circuit with power to the switch then down to the solenoid.

[graphic66]

The idle speed solonoid on the manifold is supplied constant 12 volt + power when the ignition is on and is activated by two hydrauilic switches located on each side of the tranny on the bottom with one wire connecting both switches and the solonoid. One switch is for reverse and one for forward. The fluid pressure in the tranny activates one of the switches and grounds out the wire to activate the solonoid. Your 3 position solonoid on top of the tranny has no effect on the fast idle solonoid on the manifold. To test, get out your test lamp and figure out if you have 12 volt + power at the solonoid, if not check fuses etc. to get it fixed, if you do, then simply supply ground to the other terminal, if the solonoid activates it is probably OK and your problem is possibly a broken wire from the tranny, easy to check, just follow the wire, or more likely a bad switch on the transmission. Have someone sit in the car with it running, it must be running to supply fluid pressure to activate the switches. Place the car in a forward gear and check continuity between the switch and ground, if you have no continuity you probably have a bad switch, not that uncommon. You must place the car in reverse and check the other switch also. It would be unlikely to have both switches bad. I forgot which switch is which, not that hard to figure out though.