1987 Chevrolet 350 tbi high idle

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

iamtherealJayy

Full Access Member
Joined
Nov 26, 2021
Posts
1,572
Reaction score
276
Location
Tennessee
First Name
Jacob
Truck Year
1987, 1978, 1976
Truck Model
V20, K10, K10
Engine Size
350, 350, 350
Disconnected battery swapped out iac put paper clip from a to b turned key on for 10 seconds unplugged iac started truck. It took a little bit of on the peda to keep it running but once it started it idles around 650-700 it was shaking a little bit. Iac plugged back in truck is idling around 750. And now I’m going back to work I’ll let you know how it drives
 

Bextreme04

Full Access Member
Joined
May 13, 2019
Posts
4,191
Reaction score
5,094
Location
Oregon
First Name
Eric
Truck Year
1980
Truck Model
K25
Engine Size
350-4bbl
Disconnected battery swapped out iac put paper clip from a to b turned key on for 10 seconds unplugged iac started truck. It took a little bit of on the peda to keep it running but once it started it idles around 650-700 it was shaking a little bit. Iac plugged back in truck is idling around 750. And now I’m going back to work I’ll let you know how it drives
Sounds like its doing the right things then. I would expect there might be something else not quite right if it is rough and not wanting to run at 650rpm. Its probably not enough to notice if everything else is working right, but maybe enough to negatively effect power and fuel mileage. Might be time for plugs/cap/rotor/wires, or the motor might just be getting tired and have some loss of compression on a few cylinders. It could also be nothing wrong and it just needs to sort itself out after running bad for so long. Hopefully the IAC valve was the last real problem and she runs like a champ from now on!
 

iamtherealJayy

Full Access Member
Joined
Nov 26, 2021
Posts
1,572
Reaction score
276
Location
Tennessee
First Name
Jacob
Truck Year
1987, 1978, 1976
Truck Model
V20, K10, K10
Engine Size
350, 350, 350
Well it’s got other problems but nothing major. My co worker asked why my truck smells like coolant, I’m hoping that’s just because of changing the water pump and draining the coolant and since everything has oil on it the coolant is just sticking on. And it pretty much always blows a little blue smoke on startup. I assume valve seals. I added a quart of oil between a 3000 mile oil change. So it really doesn’t use a lot between the leak and the burning. But it seems to be running decent now that I’ve spent a bunch of money. Hoping these wheels sell soon :p I’m more of a shiny person
 

iamtherealJayy

Full Access Member
Joined
Nov 26, 2021
Posts
1,572
Reaction score
276
Location
Tennessee
First Name
Jacob
Truck Year
1987, 1978, 1976
Truck Model
V20, K10, K10
Engine Size
350, 350, 350
Idle is still a little funky, if it’s just sitting there at a stop and idling sometimes it’ll just drop to 400 or lower for a second and come back. Does this sound like something that the computer should relearn and fix itself?
 

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
9,212
Reaction score
6,194
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
Idle is still a little funky, if it’s just sitting there at a stop and idling sometimes it’ll just drop to 400 or lower for a second and come back. Does this sound like something that the computer should relearn and fix itself?
sounds like a charging system issue or correcting for a vacuum leak otherwise get a fuel pressure gauge and a long hose one and some tape and get driving around the block and watching your gauge taped to the windshield at these dips

Can we see your belt drive now that it has some work done to it
 

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
9,212
Reaction score
6,194
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
Well it’s got other problems but nothing major. My co worker asked why my truck smells like coolant, I’m hoping that’s just because of changing the water pump and draining the coolant and since everything has oil on it the coolant is just sticking on. And it pretty much always blows a little blue smoke on startup. I assume valve seals. I added a quart of oil between a 3000 mile oil change. So it really doesn’t use a lot between the leak and the burning. But it seems to be running decent now that I’ve spent a bunch of money. Hoping these wheels sell soon :p I’m more of a shiny person
Put engine restorer, grey can.
I would say youre looking at valve seals more than likely if just startup. That stuff can help with that. after your truck is dialed in, change your oil because its hard to say if you have been having fuel dilution if your AFR is all over the place(as it was for a while for sure). your money spending didnt fix a lot, your learning and efforts to bring it back to where it should be are. think positive
 

iamtherealJayy

Full Access Member
Joined
Nov 26, 2021
Posts
1,572
Reaction score
276
Location
Tennessee
First Name
Jacob
Truck Year
1987, 1978, 1976
Truck Model
V20, K10, K10
Engine Size
350, 350, 350
I just did an oil change not many miles ago, and I’ve noticed the voltage gauge doesn’t pickup to normal until after 1000 or so rpm which I assume is normal because I’ve heard before it’s something in the alternator doesn’t kick in until a certain rpm. I can get a picture of the belts although they look the same as before just with a new water pump.
 

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
9,212
Reaction score
6,194
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
I just did an oil change not many miles ago, and I’ve noticed the voltage gauge doesn’t pickup to normal until after 1000 or so rpm which I assume is normal because I’ve heard before it’s something in the alternator doesn’t kick in until a certain rpm. I can get a picture of the belts although they look the same as before just with a new water pump.
thats fine. i want to see what I can see in it. Also, did you just say doesnt get to normal until 1000 or so? What voltage is it reading at "good" idle and "in gear stopped" I feel like we found you have a bad alternator or a belt should be on a smaller track of the crank/wp.

fuel injection especially in old cars but almost any car is sensitive to voltage dropping below desired especially far. an engine would probably wind down because the sensors readings would all be "lower" and things be slower, spark weaker, and in this madness your computer sees drops and then goes to change with the IAC by extending it, then its at voltage and suddenly everything is spiked in its world.

my 1990 had issues idling down to 400-500 and occassional stall when the alternator started to die
it eventually died
i was a block from my dads so I parked there, he happened to have someone elses CS130 on a shelf and we just swapped the rear case half or maybe front because the ears were different, went on my way. Got a new alt and saw the guy one day and gave him his back. he didnt even know he left one there lol.

So lets see them belts and tell us your voltage readings
 

iamtherealJayy

Full Access Member
Joined
Nov 26, 2021
Posts
1,572
Reaction score
276
Location
Tennessee
First Name
Jacob
Truck Year
1987, 1978, 1976
Truck Model
V20, K10, K10
Engine Size
350, 350, 350
The voltage is maybe 11/12 (battery power) and then after it hits 1000 it doesn’t drop again until after the truck has been shut off and started again. It’s like the alternator has a resistor or whatever you want to call it and it does kick in charging until a certain speed. I will take a picture in the morning since it’s dark and cold already tonight. The voltage reads 14? I believe that’s what straight up on the gauge says. I went and got my sister from school today and on the way home I was taking a sharp turn in neutral and the truck shut off, bumped key and it was back on. Most of the time it’s fine but occasionally it still fluctuates while in neutral. Like I drove a good 15-20 minutes after I got her and ran fan the whole time. And I spent lots of time coasting in neutral in that span of time. I was riding down gravel roads to go look at the creek. Truck got a little dirty :p nothing crazy tho I can’t risk breaking the truck
 

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
9,212
Reaction score
6,194
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
The voltage is maybe 11/12 (battery power) and then after it hits 1000 it doesn’t drop again until after the truck has been shut off and started again. It’s like the alternator has a resistor or whatever you want to call it and it does kick in charging until a certain speed. I will take a picture in the morning since it’s dark and cold already tonight. The voltage reads 14? I believe that’s what straight up on the gauge says. I went and got my sister from school today and on the way home I was taking a sharp turn in neutral and the truck shut off, bumped key and it was back on. Most of the time it’s fine but occasionally it still fluctuates while in neutral. Like I drove a good 15-20 minutes after I got her and ran fan the whole time. And I spent lots of time coasting in neutral in that span of time. I was riding down gravel roads to go look at the creek. Truck got a little dirty :p nothing crazy tho I can’t risk breaking the truck
it sounds like there is an electrical connection at fault and/or a alternator charging issue.
whats your charge cable look like, how is your ground situation, is your battery secured with a hold down, what the posts look like, and I would clean the connector and the stud and remember the alternator grounds through the case. that means the cylinder head, water pump boss(if it uses one), intake possibly, tensioner bracket, block etc are all ground paths (whichever it uses of course)

here is a mock up of my alternator and brackets from another engine because the old ones were bent
You must be registered for see images attach

all the points of contact to the bracket/hardware on the alternator should be clean, for the best ground path, then the contacts to the engine and negative cable should also be clean, for hte best ground hygeine. also a good clean charge stud, charge wire of right size and low resistance, to a good clean positive clamp, to a clean positive post. Your ground on the bracket should be clean like said, but to a good sized cable of low resistance to your negative post, like the pos, clean all around and good surface area contact.

actually, I miss spoke, it looks like the charge wire goes to the distribution block. if yours does to, I would re-reun a new wire, minding any fusible links or diodes present, if any, and make it a better cable. That block should have a good clean connection too, and I do believe it has a post that goes to the starter, and then that daisy chains to the battery.(Can soemone confirm?)
You must be registered for see images attach


here is my small charge wire. see that little thing? (heh) bad. should be bigger. bigger is better(heh)
 

iamtherealJayy

Full Access Member
Joined
Nov 26, 2021
Posts
1,572
Reaction score
276
Location
Tennessee
First Name
Jacob
Truck Year
1987, 1978, 1976
Truck Model
V20, K10, K10
Engine Size
350, 350, 350
My battery and connections to battery are good. Battery is new side post with new screws. And yes there is a tie down. The alternator is similar to yours with I believe three wires coming off the back. But since I had to remove all those brackets that could be a grounding issue. I can start to remove them and clean all the surfaces and place them back on. I had to completely remove the alternator bracket and loosen the air pump brace kinda thing? Not sure what it was but one bolt of it was over the water pump.
 

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
9,212
Reaction score
6,194
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
My battery and connections to battery are good. Battery is new side post with new screws. And yes there is a tie down. The alternator is similar to yours with I believe three wires coming off the back. But since I had to remove all those brackets that could be a grounding issue. I can start to remove them and clean all the surfaces and place them back on. I had to completely remove the alternator bracket and loosen the air pump brace kinda thing? Not sure what it was but one bolt of it was over the water pump.
pics or it didnt happen
 

iamtherealJayy

Full Access Member
Joined
Nov 26, 2021
Posts
1,572
Reaction score
276
Location
Tennessee
First Name
Jacob
Truck Year
1987, 1978, 1976
Truck Model
V20, K10, K10
Engine Size
350, 350, 350
Working on it in the morning, it’s already after nine I’ve got tomorrow off since it’s gonna be storming. I’ll get plenty of pics
 

iamtherealJayy

Full Access Member
Joined
Nov 26, 2021
Posts
1,572
Reaction score
276
Location
Tennessee
First Name
Jacob
Truck Year
1987, 1978, 1976
Truck Model
V20, K10, K10
Engine Size
350, 350, 350
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
 

iamtherealJayy

Full Access Member
Joined
Nov 26, 2021
Posts
1,572
Reaction score
276
Location
Tennessee
First Name
Jacob
Truck Year
1987, 1978, 1976
Truck Model
V20, K10, K10
Engine Size
350, 350, 350
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
 

Latest posts

Forum statistics

Threads
42,126
Posts
909,664
Members
33,618
Latest member
1975K20
Top