1987 Chevy Suburban Cold crank rough

SPARETIRE

MEMBER
1987 CHEVROLET SUBURBAN
V8
4WD
AUTOMATIC
160,000 MILES

After setting all night - fires after about 2 revolutions but will not idle on it's own, I press and release the gas pedetal to keep it going. Once it's warm it is fine, drive any speed-great acceleration and kick down, turn engine off-fires right back up <1 revolution idles slightly higer for 3-5secs then down to regular idle-IAC good.
Changed gas filter, rebuilt TBI filters and gaskets, verified MAP with vacuum meter and voltage drops from 4.7vdc down 1vdc for every 10inches pull, ohm'd out TPS with multimeter- found no dead spots, EGR holds steady when vacumm pulled on it, PCV valve new, However when I remove the rubber hose (one of three) at the front base of the TBI --this one goes over to the filter canister, nothing happens to the idle, I would think that creating a vacuum leak at the base of the TBI --would induce a higer idle? Is this telling me something?

thanks.

2 Replies

JACOBANDNICKOLAS

MECHANIC
108,269 POSTS

I agree, one would think it would cause an increased vacuum leak. Is the hose plugged?

Let me know.

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Tuesday, February 16th, 2010 AT 2:14 PM

SPARETIRE

MEMBER
3 POSTS

Hi and thanks for the intrest. Well we had 8" of snow here in North Texas last week so I didn't get to look at the truck until this afternoon on the way to work breifly. I removed the vacuum hose boot and line from the base of the Tbi and the end to the EVP canister.I was able to blow thru the line=not clogged. I reinstalled. I then removed the large vacuum line at the base of the Tbi (comes from the valve cover PCV) inducing a large vacuum, cranked the truck and of course the idle was high, using my finger to plug off part of the opening, regulated the idle, after it got warm I plugged the vacuum PCV line back in. I then removed the hose from the EVAP canister and blew in it toward the tbi and the idle stubled slightly and went back normal, left it unplugged = still smooth idle. I work tonight but tomorrow I think I'm going to Ohm out the TCS up there by the thermostat housing and see what it measures cold and then after I get it warmed up? Maybe it's there? Seems like too much gas at cold crank, that's why I have to induce a large leak, but once it's warm and starts to stumble, correct the leak I created and the truck is perfect, maybe I'll also remove the top part of the Tbi to inspect the fuel regulator--put that would not explain the excellent performance and great crank and idle after warm. Sorry so long. Been talking to my 15 and 13yr old explaining what I'm doing --gett'in them involed as much as possible.

Jay