1991 chevy 1500 5.7 tbi erratic idle

[NEUMANNZZ]

No.

[tpulliam79]

well the mechanic has still not fit me in and he says he thinks its the intake because " he's done 1000's of these intake gaskets and never had one leak" says hell pull the intake and see if the gasket is baad or in wrong and if it is hell put the new one on no charge but if its not I have to pay him labor to put the other intake on...... and due to some absolute craziness money is more than tight. question is this how hard would this be to do myself with one good arm and a friend? I did the intake gaskets on my supercharged bonneville..... doesnt seem to be that much but im not 100% on this one... I have factory service manuals for the bonneville but not the truck yet.

[NEUMANNZZ]

probably easier to do on the truck. more room.

[tpulliam79]

any body have a link to the step by step guide so as Im sure im pulling the right stuff?

[NEUMANNZZ]

not a very good guide:

http://www.autozone.com/az/cds/en_us...rInfoPages.htm

[Bandit1188]

bump

[bowtiejack]

before you go just switching intakes , get it up to temperature and spray some carb cleaner along the rails( where intake mates to the heads)and see if the idle stumbles and increases . to replace the intake- three-five hour job . buy a chiltons book . three points. get a decent torque wrench and do a 2 step torque in the right sequence. make sure the intake side rails have the block out plate at the passenger side rear . lastly use a heavy bead of black rtv at the ends instead of the paPER gaskets . and hey, do a real good oil drain and fill after cause when you first lift the intake water will mix with the oil .

[tpulliam79]

well my "mechanic" re - installed different gaskets and the other intake, and says its still doing it( idles jumping ) .. he is saying its something to do with the short block thats making the intake not seal correctly. If they machined the block from the 78 blazer when matching it with the 91 tbi heads and they did something wrong is there any way that would cause the intake not to seal or it to appear to have a leak in the intake right back at the passenger side rear corner under the egr area? he says I have to sign something saying he doesnt have to fix it again and now he wants 100 ? trying to find out if I need a new or different short block or a different mechanic.. when not at idle it runs great

[NEUMANNZZ]

if the gap is too wide because someone machined to much off the block or incorrectly machine the head intake surface differently.
Makes sense to me. maybe its time to save up and get a different engine.

[Jasper911]

Yuck, feel the pain.

I'm glad I'm not the only one dumping tons of money into an old truck. Mines doing similar stuff. Replaced the 305 with a 355 roller with Comp cams computer cam/flat tops/roller rockers etc. The 305 seemed worn out and ran rich, but still having same problems with new engine.

Might want to check the vehicle speed sensor. Mine was pretty jacked up looking and surely no good, but still not my problem.

Interested to see if there's any closure on this one.

I wouldn't go looking for a new engine just yet.

[Jasper911]

Oh,

Just realized a pattern tonight. When I've got a full or mostly full tank, the truck runs great. Just filled up with 14 gallons a while ago. Was running like a dog before I did. It seemed like the truck would run great for a few days then go down hill and back to its old ways. I never kept a lot of gas in it until I started breaking in the new engine. I also have an erratic tank sender...which usually doesn't work. I think I'm gonna go ahead and replace the sender and the pump while I'm in there.

[Rabbitiswise70]

Originally Posted by Jasper911

Oh,

Just realized a pattern tonight. When I've got a full or mostly full tank, the truck runs great. Just filled up with 14 gallons a while ago. Was running like a dog before I did. It seemed like the truck would run great for a few days then go down hill and back to its old ways. I never kept a lot of gas in it until I started breaking in the new engine. I also have an erratic tank sender...which usually doesn't work. I think I'm gonna go ahead and replace the sender and the pump while I'm in there.

Try a new gas cap. Some trucks like a little more pressure in the tank. If its an orginal cap,,it could be releaving too much.

Just a thought. Let me know if that works for you.

[tpulliam79]

my gas tank has nothing to do with it the engine isn't missing when cold anymore just surging at idle. It runs great except at idle, I have to get it through emissions in the next couple weeks, if nothing else ill get a waiver for it and go from there. I really like the truck and think ill just drive it until i can afford to put a new engine in it. think i may be trading my supercharged bonneville for a 96 tahoe ( once my mechanic checks it out).

[Jasper911]

Originally Posted by tpulliam79

my gas tank has nothing to do with it the engine isn't missing when cold anymore just surging at idle. It runs great except at idle, I have to get it through emissions in the next couple weeks, if nothing else ill get a waiver for it and go from there. I really like the truck and think ill just drive it until i can afford to put a new engine in it. think i may be trading my supercharged bonneville for a 96 tahoe ( once my mechanic checks it out).

I wouldn't be so quick. This sort of thing just set me back about four grand!!!!

[Rabbitiswise70]

Does the Truck still have the charcol canister still hook up? If yes, check the lines for breaks. It could be causing a vac leak.

[tpulliam79]

checked lines no leak... new intake and gaskets and now it seems to only do it in park and reverse? I love my truck but am real close to trading her in ....gotts get through emissions and at this point its not gonna happen . Not to mention the 70 inches of snow we have gotten in the last 3 weeks.

[FordeatinZ71]

if you really love it and don't wanna trade it, then just give it to a shop to fix. you are wasting time troubleguessing and wasting money too...if you can't figure it out (we've all been there) then just let a decent shop do it for ya. i have a friend in Seattle who might be willing to lend a hand...if i can get ahold of him...

[tpulliam79]

its been to three shops 2 said intake leak at rear passenger corner I have had the gaskets done twice and put a new intake manifold on also the other shop saya its cat and muffler, but cat and muffler wouldnt be noticable only at idle

[cancritter]

l feel for ya...have you had it in to a GM dealer yet?
like yourself l dont mind payin the extra buck to have it done right the first time and if theres a prob the balls to stand behind thier work and tell ya straight up what prob is....
l realy dont know what to say..could be half a dozen things and for most here is like a doc doing a diagnosis over the phone...personaly ld take it to a reputable gm dealer and let them have a boo at it...at least youll have some sorta warentee in the end or a good idea whats wrong...
at this point have fergoten if you have internal engine mods to deal with as well...if so you gotta drag the whole thing to a dyno/mech shop or your just grabbin at straws trying to get it set up

[Rabbitiswise70]

Originally Posted by tpulliam79

checked lines no leak... new intake and gaskets and now it seems to only do it in park and reverse? I love my truck but am real close to trading her in ....gotts get through emissions and at this point its not gonna happen . Not to mention the 70 inches of snow we have gotten in the last 3 weeks.

Do you know some that can hook a scanner(not a code reader) to look at data, and possible pull the soft codes(codes that do not trip check engine light on) if there are any?

The other question would be, has the O2 Sensor been replaced? That sometimes can cause it. Thats were a scanner would come in handy, you could see if the O2 is switching or not. Also you could see if the IAC is working properly. In fact trying tapping the IAC when in park and see if the idle changes.