Crap idle due to bad brake booster?

So I replaced my TPS because my idle was crap like 250ish and went into limp home mode. '89 4.0 stock motor with auto. Replaced the TPS and not in limp home mode anymore but idle still is around 250ish and yes it was adjusted. My brakes are garbage like on the floor so I know my booster is bad and am swapping in a dual diaphram (sp?) one this weekend. My question is, when I take off the vacuum line to the booster my idle goes up to 800 which is about where it should be but once I hook back the line it's back to almost dying. So is the booster causing the drop? Will replacing it put my idle where it should be? Thanks...

Good chance that the new booster will take care of this idle issue.

And as you know the booster is bad, that makes the swap a no-brainer.

Let us know if this resolves your idle.

The booster can not cause a low idle. It can cause a high idle if it's leaking vacumn internally, or if you unhook the hose and let it hang as you did. A bad booster will usually manifest as a hard brake pedal and poor braking. You're pedal on the floor points to needing to bleed the brakes or a bad master.

On the low idle, have you cleaned the throttle body and verified that the idle air controller motor is working? The renix doesn't have a limp home mode. You might also want to check your EGR valve as that can cause a rough, low idle. http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

I assumed it had a limp home mode since it wouldnt shift above 2nd with the tps bad. New tps and it is fine besides bad idle. I am cleaning the throttle body and checking the air intake tomorrow and the egr is good too. Brakes have been bled and through troubleshooting on here, it points to my booster being shot but my new set up that i will be putting in is master cylinder and all so it wont matter.

Your bad shifting was the TPS. BTW, did you adjust it?

Renix Jeeps never limp!

LOL

There is a valve (Proportional valve? supposed to equalize pressure to front and rear breaks I think) after the MC that can trap air, and defy bleeding, and also cause the brake peddle on the floor, so can worn brake parts, pads, drums, and rotors worn past the limits, and a bad, new MC. I have also heard that the rubber brake hoses can cause it just before they blow up, out.