1987 Chevrolet 350 tbi high idle

[gmbellew]

may make sure your harnesses to all the sensors are routed so they don't touch as much as possible. I had a weird issue where the TPS harness was run too close to the MAP and CTS harness and it was causing some weird interference and causing high idle and non-idle down conditions.

 

[iamtherealJayy]

I have a brand new throttle position sensor I installed but removed because it did Nothing. Map sensor is new aswell. I’ll check wiring and plugs.

 

[AuroraGirl]

Yes I have done the key on unplug iac procedure. I can do it again. I also noticed the truck has gotten worse with the bubbling sound while idling it sounds like a bubble coming through the exhaust. I don’t know how to explain the sounds. Any ideas on what that might be?

Coolant not bled, that could be messing with your ECT reading which will affect running behavior

 

[iamtherealJayy]

The truck doesn’t overheat anymore but I can check coolant. I noticed the bubble sound one day coasting down a hill after I put the truck in neutral. But today leaving work it was “bubbling” while idling until I left. I’ll try to get a sound clip of it since I honestly don’t know what to call the sound other than a bubbling noise. It sounds like you can hear it rolling through the exhaust and a pop out the tip, not an aggressive pop like a backfire or anything but just like a bubble popping.

 

[iamtherealJayy]

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Here’s a clip of the sound I’m trying to describe. Not a perfect clip but maybe you can hear what I’m referring to.

 

[Gene King]

I don't have much advice but I sympathize with you mate. I think if I had 37 forum pages worth of problems with my truck I'd destroy it out of spite

 

[iamtherealJayy]

37 pages is slight work, I have multiple threads with several pages… always got a new problem. The truck has occasionally done this noise but it has started doing it more and more but it’s not the first start of the day but more when I start it to leave work and it’s hot outside and when I start it after lunch to go back to work

 

[AuroraGirl]

37 pages is slight work, I have multiple threads with several pages… always got a new problem. The truck has occasionally done this noise but it has started doing it more and more but it’s not the first start of the day but more when I start it to leave work and it’s hot outside and when I start it after lunch to go back to work

plus a lot is the same topic but re discussed. not a dig, but its the process of working through the set problems not that he has 37 pages of continued issues just coming out after eachother(Like if I were to start a full resto on mine today lol)

 

[AuroraGirl]

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Here’s a clip of the sound I’m trying to describe. Not a perfect clip but maybe you can hear what I’m referring to.

that would be birds , likely song type but im not racist so maybe robins/cardinals/etc
also, the cutout noise sounds like a truck exhaust to me.
If I didnt have 300 exhaust leaks and barely done exhaust i would imagine mine would sound similar. also if timed with light*

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also yes rust. rip.


If you can, can you show your exhaust from the back facing inward in one shot?

this is something extreme i dont think yours looks like, but

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Imagine all the places your pipes connect, the muffler(s) and pipe(s) all get mounted. you dont want to have a metal connection directly between the exhaust and the truck/axle/driveline except for where th manifolds/O2 sensor/and eachother existif anything is loose or binding you may be touching or shifting with running

 

[iamtherealJayy]

I’ll get a better video of my exhaust noise from behind I was in rush to get back to work in the video. I’ll also get a photo of exhaust system.

 

[iamtherealJayy]

Alright here’s a photo I took at work since today the truck is making all kinds of noises from exhaust.

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The exhaust is a single pipe that splits before rear axle with a tube muffler of some sort and maybe a cat? Not sure I’ll get a pic. And here’s two videos of the noises is was making and the surging idle. It runs fine cold but once it’s warm js starts to surge and the exhaust pops are right after startup, if you blip the throttle it stops. It may also be running rich a little bit since it was burning my eyes standing behind it videoing.
Here’s the tachometer surging

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And here’s the exhaust clip, at around 1 minute I turn the truck off and start it back and after the idle comes back down (1200 when I started around 500-550 when the popping starts)

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I don’t know if this is possibly a sensor ? Plugs? I’m out of ideas on it but when it’s cold the idle doesn’t get down low enough to make the noise and the truck runs fine, once it’s warm and it fires up instantly the idle drops and it’s running weird. I moved the truck earlier at work and when I was in reverse the truck was making more of a backfire noise, it was a more aggressive popping than in the video provided.

 

[iamtherealJayy]

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Here’s a photo of the rest of the exhaust

 

[Bextreme04]

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Here’s a photo of the rest of the exhaust

wow, that looks like a catalytic converter? Installed WAY back in the exhaust system. I'd pull the exhaust pipe right before the cat and fire it up, see if it runs WAY better. You might have a destroyed/plugged cat since it cant get hot enough that far downstream.

 

[iamtherealJayy]

Sorry for confusion, the cat is by the Dow pipe, not in the back, it go w manifolds to a crossover that joins both sides to a cat to a tube muffler to a split to tips.

 

[AuroraGirl]

Alright here’s a photo I took at work since today the truck is making all kinds of noises from exhaust.

You must be registered for see images attach

The exhaust is a single pipe that splits before rear axle with a tube muffler of some sort and maybe a cat? Not sure I’ll get a pic. And here’s two videos of the noises is was making and the surging idle. It runs fine cold but once it’s warm js starts to surge and the exhaust pops are right after startup, if you blip the throttle it stops. It may also be running rich a little bit since it was burning my eyes standing behind it videoing.
Here’s the tachometer surging

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And here’s the exhaust clip, at around 1 minute I turn the truck off and start it back and after the idle comes back down (1200 when I started around 500-550 when the popping starts)

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I don’t know if this is possibly a sensor ? Plugs? I’m out of ideas on it but when it’s cold the idle doesn’t get down low enough to make the noise and the truck runs fine, once it’s warm and it fires up instantly the idle drops and it’s running weird. I moved the truck earlier at work and when I was in reverse the truck was making more of a backfire noise, it was a more aggressive popping than in the video provided.

what drives your tachometer? I didnt realize you had an aftermarket not a stock gauge, my bad.

Sorry for confusion, the cat is by the Dow pipe, not in the back, it go w manifolds to a crossover that joins both sides to a cat to a tube muffler to a split to tips.

Your exhaust diameter is HUGE for a gas engine, i think your issue with the cat converter as bex noted may be the same. if it cant get hot its gonna plug. if its old in anyway, its probably not the newer/more efficient designs, and its probably
also it appears the cat converter is universal in design and it looks like it needs hangers. your dont have hangers and you have clamps in it between front and back, the front bolted to the engine. its probably pivoting on those clamps because its definitely going to weak point in between front and back solid mountings such that I would definitely unclamp it, pull it off. inspect it, run the truck as is for a short time, see if it improves running and if you want to put it back on, get the band type clamps and spread the load forces or utilize the hangers on the sides but i dont know how you would best hang it there without some custom stuff lol