Replaced the vacuum pump but.....

[techspy]

Well, when I first drove my S4, I noticed 2 problems right off. The EBV was not opening no matter what the operating time/temp. Also, no matter what position the a/c controls were in, I got no hot air from any vents. So, I wired the EBV open, and decided I would tackle the heat issue later. Turns out the vacuum pump was bad. I ordered a new one from gmpartsdirect.com (after NAPA told me it wasn't available), and got it today at a cheaper price than directly from GM, $30 cheaper. So I installed the pump and the heater is working perfectly now. I have the EBV back to normal, but unless it is working perfectly, I will wire it back open. Time will tell on that one. I also reset the ECM so it can learn to operate correctly with a vacuum pump again. Anyway, during my running down the problem of the pump I discovered that the turbo actuator etc. runs off manifold pressure or vacuum, and the throttle jacking capsule, the a/c controls and the EBV run off vacuum from the vacuum pump. Oddly enough my idle has always been ok, and didn't seem to have any detrimental effects of no vacuum pump. Anyone have any comments on this? Is there a system other than the throttle jacking capsule that takes care of the idle control? Or does the throttle jacking capsule not related to the idle normally but is used for when the a/c compressor is on etc? Does anyone know of any other system that runs off of the vacuum pump? And lastly, is the vacuum pump supposed to cycle only when needed? (which mine seems to be doing now) Or should it be running constantly with the ignition?

Thanks
John
94 S4

[JK1]

John,

I could be wrong but I think the throttle jacking capsule only controls the idle for the cold start function to give the higher idle for warmup. I think the Idle Air Control (IAC) controls the actual idle from the ECM and is not a function of the vacuum pump.

The pump should activate for a few seconds when the key is turned on to pressurize the system and then only when needed.

You experts out there correct me if I'm wrong but I think that's how it works.

[techspy]

I think you are right. A little further reading in the manual explained it. Apparantly the throttle jacking capsule is only to raise the idle rpm when the EBV is closed. I just hope the EBV works correctly now as I have just moved to a state that tests the exhaust in the inspection process and I would like the complete emissions system working.

John
94 S4

[lotusespritworld]

EBPV is only used to warm the CAT up quicker from a cold start, so unless your emission tests are done from cold, then you don't need it.

kato
Lotus Esprit World

[JK1]

kato is correct.

I removed the butterfly valve from the EBPV and removed the vacuum solenoid but left the throttle jacking capsule intact. My car still idles high at cold start and drops down when warm as it should.