Picked up an 87 Chevy 350 TBI, 700r4, 2wd, blah blah. Runs great, but if it sits for awhile, when it starts it idles really low. Sometime it will stall out, till you start it 3-4 times. Once it warms up, it idles real high. No tach, but guessing 1200 r's. Someone said the TBI gasket sucking air, but that wouldn't account for the low idle when cold. Thought about the TPS, but more I think it could be the IAC??
CK5
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TBI idle issues
- Thread starter b454rat
- Start date
I'd not be guessing it's any of the hardware other than gaskets or vacuum lines leaking. Rarely does any of that stuff go bad, certainly not as often as it's replaced trying to guess the problem.
Putting it on a scanner would help too, CTS might be dead, etc.
Putting it on a scanner would help too, CTS might be dead, etc.
I agree with Dorian, it's time for a scan tool.
The check engine light comes on, but the speedo doesn't work, so probly VSS related. Checked any vacuum lines, replaced one, but that was all that was found. I need to get a can of either and spray around the base of the TBI and hoses. If there is a leak the either will make the R's rise and fall. I think a buddy has a scanner to check for codes and parimeters...
Supposedly VSS doesn't make a difference in idle on the TBI trucks. On my TPI, it most definitely affects idle...mine starts idling worse and worse as time goes on, eventually to the point it wants to stall coming to a stop. The TBI folks here though are adamant that VSS isn't a factor on their rigs, and I'm not disagreeing.
If the speedo doesn't work, and the VSS doesn't either, I'd fix it first, assuming it won't hurt your budget too much. Used parts are my friend.
Lack of VSS *might* put the vehicle in some sort of limp mode, since it IS a code triggering issue, it may be tied into EGR, EVAP, something along those lines, that is important enough for the ECM to limp.
Won't hurt to run your codes first, make sure VSS isn't the only one you are getting.
If the speedo doesn't work, and the VSS doesn't either, I'd fix it first, assuming it won't hurt your budget too much. Used parts are my friend.
Lack of VSS *might* put the vehicle in some sort of limp mode, since it IS a code triggering issue, it may be tied into EGR, EVAP, something along those lines, that is important enough for the ECM to limp.
Won't hurt to run your codes first, make sure VSS isn't the only one you are getting.
I dont' think it's VSS. My 89 didn't have VSS, and that ran great. Fixing the speedo won't be hard, just haven't had much time to look at it yet. Waiting on parts to make a 4wd....The truck sat for awhile before I bought it, not sure if that could make a sensor or something go out of whack. I put seaform thru it and a couple tanks of gas, runs better, but the high idle has got me wondering, and irritated...
Pull the codes, might be something else to give you a clue in there.
Check the codes, it's free and easy.
http://coloradok5.com/forums/showthread.php?t=240425
1987 VSS I think is behind the speedo...
Thunder
3/4 ton status
I would defiantly check the TB gasket and other vacuum lines for leaks. Bad idle/stalling when cold and high idle when hot are classic signs of a vacuum leak.
Start with the simple obvious stuff first.
Start with the simple obvious stuff first.
Talked to a buddy who was a mechanic for a years, he pretty much said the same thing. Going right now to change the TBI gasket....Hoepfully that will do the trick, I got the parts from DIY4x to make it a 4wd.....
Changed the TBI gasket, seems to idle little better, but didn't really have a chance to let it run. Took it up the road, went to turn around and just about ran out of gas. Once I get some gas, let it warm up fully, see how it is then, and then try to get some codes...hopefully then I can sling some axles underneath it.....
how did the old gasket look? sucked in or what?
Didn't notice anything obvious. The center looked like it got folded, but I might have done that getting the TBI out of the way to get the gasket out....I'm gonna try the IAC next, since the truck sat for who knows how long, could be gummed up...
Thunder
3/4 ton status
Might want to check/ clean the EGR too. It may be leaking a bit at idle.
Maybe i should ask people to just send me all there swapped parts so i can have back-ups on hand. 
It's not hard to test each item or clean them first before replacing them. I wish i had all the money people spend on swapping good parts for new parts.
It's not hard to test each item or clean them first before replacing them. I wish i had all the money people spend on swapping good parts for new parts.
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x2. I sure hope people put these parts on the shelf somewhere as backups, otherwise thats a lot of good money going to the dump. 
IAC's RARELY go bad, and CAN be cleaned/tested if you suspect them. But bad idle is not a reason to suspect IAC.
IAC's RARELY go bad, and CAN be cleaned/tested if you suspect them. But bad idle is not a reason to suspect IAC.
Only thing I replaced was the TBI gasket. I didn't have a wrench to take it off. Even if I did/do replace it, it will be free at the local junkyard...
Wrecking yard freebies ARE easier to swap than cleaning/testing existing, usually. (except that damn gasket on the IAC)
Gonna try to work on it again tomorrow. Buddy has a scanner, so maybe it's something stupid, hopefully pinpoint what needs to be fixed or replaced. Getting ansy (sp?) to make it a 4wd....
I bought a Chilton book on fuel injection, not really the one you want for a singular truck. But it has procedures to test every part except ECM I thing.
