Chevrolet Repair: 1994 S10 Vortec runs rough at idle, s10 blazer, vortec engine

Question
Hi,
I understand it is possible that this may be two different problems, one thing I did not mention is when I pull the vacuum hose off the power brake boster, thus creating a rather large vacuum leak (it'll suck you finger in), the vehicle runs much better (probably leans out the mixture) and if I pull the check valve out of the boster unit it releases "air", sounds as if you just popped the top on a cold one.
Any additional ideas or advice.

Thanks
Ed
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Followup To

Question -
Hi Mark,

I was reading a question related to this subject you answered on 2/18/2006. I also have a 1994 S10 Blazer with a Vortec engine with VIN "W"; the truck has been running rough at idle which I have attributed to a rich fule mixture. I have had the truck on an anylizer an it comes up with an EGR failure however the EGR is only a year old and when I removed it there is no sign of excessive carbon build up. By the way it is a digital EGR, a bench test shows it is operating properly. There is heavy carbon out of the tailpipe and the brake pedal gets excessivly hard when the truck is running rough. I have not yet pulled the plugs as you suggested in your previous answer on this subject. Also you mentioned the CPI unit could be the problem. At the sake of sounding stupid; what is the CPI?
Thanks for your help. I have been out of the auto repair game for longer than I want to admit.
Ed Wade


Answer -
Hello ED,
The CPI unit is central point injection. It consists of a single injector, inside the plenum, with plastic lines going to each intake runner, where there is a poppet valve for each. When the injector opens, the pressure overcomes the poppet, and sprays fuel into the runners.

If one of those lines is cracked, or a poppet stuck open, it will cause excess fuel to be dumped in.

Your brake symptom, however, leads me to believe yours is a vacuum problem.
If the egr valve sticks open, it will act like a large vacuum leak, and could cause the lack of power brakes.

But...any other loss of vacuum could do the same thing, and if the cause of the vacuum loss happened to be in the brake booster system, that could cause the engine to act like the egr valve is open.

I would connect a vacuum gauge to the engine, and go for a ride.

Van

Answer
Hi Ed,
Go to this page and read about it.
Something mentioned down in the middle is the idle air control valve.
Yours may be sticking.

http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/1


Van