1987 Chevrolet 350 tbi high idle

[iamtherealJayy]

@gmbellew ive got one of those aldl to usb cables on the way, be here next week. Figure nice to have. I’m going to use one of those IR thermometers tomorrow and measure temp at intake manifold, both cylinder heads, and block. I’m more concerned about the heating than the idle. Although the new thermostat made the idle worse? It literally screams at stop signs. Idling at 1600 I can pretty much let off the clutch on flat ground and take off without hitting the accelerator. And then pulling it out of gear rolling to a stop it jumps up to 2500(hitting brakes doesn’t effect it, read somewhere if the brakes make it change could be vacuum booster or something) and doesn’t come down until after I’m fully at a stop.

 

[gmbellew]

I'd hit up the service manual, cooling system and start doing those checks before I started randomly messing with any computer stuff.

also, turning the heat on full blast will actually help lower engine temps because it pulls heat out of the coolant passing through the heater core.

 

[gmbellew]

did you force the IAC closed and check idle speed per the test in post #8? or remove the IAC and plug the TBI hole and check idle speed?

 

[iamtherealJayy]

@gmbellew no I have no got that far I’m trying to figure the running hot issue now. I dunno how quite to put it but I’m not sure I can afford whatever a shop would want to do to it in all honesty. I’m only 19 and I build houses. Works slow right now since it’s so cold. I’m trying to get it fixed for less than a few hundred dollars. I’ve probably got a few to spare but rather not spend a thousand bucks right now.

 

[iamtherealJayy]

I'd hit up the service manual, cooling system and start doing those checks before I started randomly messing with any computer stuff.

also, turning the heat on full blast will actually help lower engine temps because it pulls heat out of the coolant passing through the heater core.

The setting it always on heater(non a/c cab) I just had blower motor off. So wouldn’t the heat technically be on? I didn’t think about that until now. So if having it on helps I don’t want to know what the temps would be with the heat off.

 

[gmbellew]

The setting it always on heater(non a/c cab) I just had blower motor off. So wouldn’t the heat technically be on? I didn’t think about that until now. So if having it on helps I don’t want to know what the temps would be with the heat off.

the air flow across the heater core is what will draw heat out of the system. put blower on high to help reduce overheating.

 

[gmbellew]

see section 6B of the 1987 service manual. it has all the checks and diagnostics for an overheating engine.

https://www.gmsquarebody.com/threads/1973-1991-service-manuals.14499/

while you are there, I'd recommend downloading all the manuals for your 1987. they are invaluable for troubleshooting, diagnostics, and repair.

 

[iamtherealJayy]

Thank you. I’ll get them ready for tomorrow, it’s after nine now. Days are just too short to accomplish everything I need to get done.

 

[iamtherealJayy]

@gmbellew i read a good portion of the cooling system trouble shooting. Like I said yesterday it was bubbling and that’s a sign of? Exhaust gases leaking into the cooling system? It says in the manual if you hit the gas and it bubbles up than that’s exhaust gases. Well my idle is sitting at 1600… I’m basically holding the throttle open. Maybe that’s why it was flowing out of the radiator?

 

[gmbellew]

check the thermostat operation like this

 

[gmbellew]

if thermostat is ok, next in the list is radiator cap. is it new like the radiator? I am assuming no visible coolant leaks. after that is the serpentine or V belt tension (your pics show the 87 is a mixed belt system). after that is upper hose collapsed. after that is obvious radiator blockages (check temp across radiator as described in manual). if all that checks, I'd suspect the water pump or plugged passages somewhere as described in the "unusual" problems section.

 

[AuroraGirl]

How would I go about adjusting the fan closer to engine? The fan spins with engine running and changes with rpm. The cap is new as well replaced it when I replaced radiator. Could it be the spring in radiator? I believe there were different sizes? Maybe? I can’t remember. I just got recommended by oreillys. It was around 30° this morning on my way to work, the heat was nice but I left it turned off hoping to keep temps down since it was sitting between 210-260, so not sure how a fan moving air would help any better than it already being below freezing outside and moving 45-55mph. @AuroraGirl where is the ecm and prom stuff located? I can look into it but I’m not sure where it is. Also is it easy to mess something up if it start messing with it? Or is it mostly straight forward? I assume disconnect battery it messing with that so you don’t short anything? I haven’t gotten to reading all the files you sent above but I’m going to try to when I get back home.

i wouldnt touch the ECM then just to avoid issues there.
Also, I was saying a fan like a household fan while not moving. the cold ambient wont do much to your temps if you arent moving compared to hotter. basically if it will overheat idling, then try a fan to keep it from is what i was getting at. Also, using your heater on full blast would help your truck cool.

Because your fan looks off, we should verify you have a serpentine fan not a poly v or v belt fan. Directionally different, I believe?

 

[AuroraGirl]

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this is one of the documents i sent, worth checking a vin to see if its a concern that could be at play

 

[iamtherealJayy]

@gmbellew is a coolant stick something I can get like at a store? I read it was just a pencil like wax stick. Yes the radiator cap is new I bought a new one when I got new radiator. The belts are new(all three) and there is no tensioner, you set the tension by moving the alternator power steering etc whatever that belt is spinning. The upper radiator hose is new approximately maybe 7 months? I’m going to try and get a temp reader thing today and read the temps of the engine all over, check radiator in all spots, hoses, thermostat housing, heads, block, intake manifold, etc.

 

[gmbellew]

I am not sure if those wax sticks can still be found. if you plan to have an IR thermometer, I'd just use that to monitor thermostat operation to test it.