Pirate Twisty

Ok first off, let me thank you all for the wealth of info I have already found here before registering! You guys are lifesavers!

So, a few weeks ago I bought an 87 300E in reasonably good condition. Jump started it, drove it out of the snowbank it had been living in, and drove her 40 miles home on the interstate (so far, so good!) The car runs and drives great! I've been spending my time chasing the usual electrical demons, like the seats, climate control, windows, blah blah blah. All has been well until today.......

Today, I started the car at lunch time and the RPM's went straight to the top! Obviously, I shut it right down, checked the gas pedal, and tried again...... Same thing!

Tried this 4 times with the same result, then, it was ok....... Off to lunch I went.

Later, at home, I played around some more, and here what I've found:
If I start the car with my foot OFF the brake, the RPM's skyrocket. If I start the car with my foot ON the brake, it's fine; idles around 800 and stays there, even after removing my foot from the brake. Also, I can knock down the high RPM's by touching the brake! (car is still in park).

What in the living hell is going on? thanks in advance for any input!

ptoro01

You have a brake booster issue. It's vacuum assisted. Might be a stuck check valve somewhere.

Pirate Twisty

A brake booster issue, you say? That's probably not where I would have looked! As it turns out, I have some brake issues to deal with too! I didn't mention that because I didn't see any possible relationship!
But since you mentioned it.... I have to "double pump" the brakes to get any real pressure (I assumed they just hadn't been bled correctly). Could this be related?

ptoro01

nahhh ... only absolutely.

Pirate Twisty

Ok ptoro, riddle me this: I don't know if this is a symptom, or the cause, but the culprit is the cruise control actuator. The car kept taking off down the road at full tilt today (which was somewhat alarming!). I realized that gas pedal was moving of its own free will, so I reached up and hit the cruise disengage and it went back to normal. But it kept doing it!
Needless to say, driving around with one hand on the cruise control switch is a tad inconvenient, so I got home and set about trying to disconnect it. So, I'm standing there, looking over the throttle linkage setup, with the engine OFF, but the key ON, when right before my eyes, the cruise control kicks on and opens the throttle ALL THE WAY!!
So, anyways, I found where the actuator plugs in, and unplugged it! Seems fine now. I don't actually care one little bit about cruise control, but I would still like to know what happened there (just 'cuz). You never know, I might fix it if I run out of things to repair

ptoro01

That's funny. So then perhaps you have the typical surging cruise control module symptom with a bad switch on the stalk ????

How is your blinker stalk? Fill up on blinker fluid lately ???

Pirate Twisty

Blinker stalk is fine (for that matter, the cruise stalk FEELS fine). I just had the blinker fluid and filter changed, so that should be good to go!

ptoro01

If it turns cruise off then it's sorta functional. Say does your cruise control work fine otherwise?

You said there were electrical problems, fix them? Many of them related to the fuse box?

The pressing the brake makes sense as that disables cruise. The double pump I don't get. Even really old fluid should work 'fine'. Are you losing brake fluid?

Maybe the blinker fluid was just overfilled?

Pirate Twisty

Truthfully, I had never tried the cruise. 99.9% of my driving is around town, and even on the highway I prefer to be the one driving the car! No, not losing any brake fluid. I suspect that the previous owner just didn't bleed the brakes correctly. I'll worry about that when my new rear calipers get here (I had one seized right up, so I pulled it off, drove a chunk of wood between the pads, and zip tied it out the way---laugh all you want, it's been doing fine!). The brakes work on the first pump, but the pedal pressure increases significantly on the second press.

ptoro01

Good god! Talk about a riddle....

Yea the brakes need that second pump to first clamp on the wood and then squeeze, until the 2x4 explodes, caliper blows its piston and your e brake gets to save the day. BUT very cool "middle of the sahara" fix.

Well we're trying to find why the actuator kicks on full. Not many parts to the cruise system...

Kestas

Perhaps the "accel" feature of the stalk is stuck on the ON position.