1987 Chevrolet 350 tbi high idle

[AuroraGirl]

Alright I’m still having issues, the truck hasn’t stalled in a while, but if I’m going down the road I can push the clutch and the rpms don’t drop for a few seconds and they slowly go down. The truck majority of the time idles correctly once warm, but it takes a while for it to drop down. Say I’m driving and throw it in neutral to stop the truck will still be around 1200 by the time I come to a stop, and around 800 by the time I take off again. I’m not sure if this is like an advance weight sticking in the distributor or a different vacuum leak ir something. I have no idea, but it’s starting to bother me more for some reason. It isn’t hard to shift I can go through the gears no problem and the rpm drops once I’m in the next gear but it doesn’t drop if I push the clutch in or pull it out of gear. At least not for several seconds.

also, go back to the beginning. those TSBs i posted, I think they have answers to what you seek

 

[iamtherealJayy]

The idle is fine majority of the time, other times not so much. If it’s just idling it sits at 650 ish. If I’m moving and then stop the idle stays around 1000 before eventually dropping back down. If I’m driving and press the clutch say in Low and the engine is at around 1000 rpm the speed will actually increase when I release the load by pressing the clutch.

 

[AuroraGirl]

The idle is fine majority of the time, other times not so much. If it’s just idling it sits at 650 ish. If I’m moving and then stop the idle stays around 1000 before eventually dropping back down. If I’m driving and press the clutch say in Low and the engine is at around 1000 rpm the speed will actually increase when I release the load by pressing the clutch.

sounds like its possibly normal behavior with early TBI. When you release the load the engine has less , well, load, so its momentarily speeds up all things else equal. then the IAC notices the idle is high, and it brings it down.

 

[AuroraGirl]

'87 TBI - High idle and stick gas pedal? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

'87 TBI - High idle and stick gas pedal? The 1973 - 1987 Chevrolet & GMC Squarebody Pickups Message Board

67-72chevytrucks.com

 

[iamtherealJayy]

I understand a little bit of increase but doubling rpm to 2000? I’ll try to get a driving clip on the way to work tomorrow if I remember. I’m also fine with an increase for a few seconds but it generally doesn’t return back to regular idle by the time I have to take off again. The teuck rarely sees below 1000 rpm

 

[AuroraGirl]

I understand a little bit of increase but doubling rpm to 2000? I’ll try to get a driving clip on the way to work tomorrow if I remember. I’m also fine with an increase for a few seconds but it generally doesn’t return back to regular idle by the time I have to take off again. The teuck rarely sees below 1000 rpm

The link I posted indicated check TBI gasket(never hurts to do it anyway) and also throttle cable. If i recall correctly, I thought I saw some potential issues on your throttle cable setup? They are cheap enough but you can check it out

 

[iamtherealJayy]

I’ll check the cable in morning, thanks for that. I agree my throttle isn’t easy to press by any means. There is no easing into it, by the time you get the throttle to move the rpms shoot up to ~1500 and then you let off to lower rpms when taking off.

 

[AuroraGirl]

I’ll check the cable in morning, thanks for that. I agree my throttle isn’t easy to press by any means. There is no easing into it, by the time you get the throttle to move the rpms shoot up to ~1500 and then you let off to lower rpms when taking off.

Id almost bet this is part of it then, those extra springs I think I saw? if you have issues moving it smoothly it probably has issues returning smoothly or at the right "speed" possibly

 

[iamtherealJayy]

I replaced the throttle body gasket and cleaned the throttle body and injectors. You noticed my throttle had two “carburetor” return springs on there. I removed one but I don’t remember if I removed the second. I can check the cable and see what the truck idles at with cable disconnected and how hard it is to press pedal with nothing attached. Also will make sure both springs are removed. I’ll also check time it takes for engine to return to idle after a blip of throttle. When hitting the pedal it takes what seems like forever for it to settle back down.

 

[GTP51]

Had same issue , was worn throttle shaft, replaced the TBI unit problem solved

 

[iamtherealJayy]

With a worm throttle shaft, will there be visible play in the shaft by up and down side to side? How do I check that prior to dumping money into parts that I don’t know if I need? It seems if there was a throttle shaft problem that would cause a vacuum leak? My truck idles around 650 it just takes forever to get back down to 650.

 

[iamtherealJayy]

Removed the throttle cable and the weight of the pedal on the other end pulled the cable and it moved freely. I removed the springs and the pedal is easier to press but over all the truck still idles funky. When the throttle cable was removed I blipped the throttle and it still stayed high for a few seconds before dropping back down.

 

[Bextreme04]

Did you ever do the IAC reset procedure?

 

[AuroraGirl]

Removed the throttle cable and the weight of the pedal on the other end pulled the cable and it moved freely. I removed the springs and the pedal is easier to press but over all the truck still idles funky. When the throttle cable was removed I blipped the throttle and it still stayed high for a few seconds before dropping back down.

now that you changed factors you would want to reset your battery cable to clear learned behaviors, and what bex said too

 

[iamtherealJayy]

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?