1987 Chevrolet 350 tbi high idle

The sound is similar to like an electric fuel pump sound, or a relay in a sort. I didn’t get to finish the procedure I’ll try again later I had to go do something. Maybe my iac is plugged up. And last time I did the codes from flashes there was none but I’ll check them again just incase.

iamtherealJayy said:

I just drove for a bit and connected the paper clip and turned ignition on and service engine light started flashing and I could hear a clicking sound from I assume the iac?

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The IAC would be clicking yes because its trying to close while you do this. If you dont touch the IAC it just goes back to what it was doing when you use your truck. If you dont need to adjust minimum idle or IAC, I wouldnt touch things. But its part of how the thing is adjusted. If it was an electric fan vehicle, so prob not a TBI but TPI or other kind of ALDL equipped GM, there would be cooling fans going on and if the clicking was happening i would guess it would be relay failure. but You have TBI truck so that should be ok.

iamtherealJayy said:

The sound is similar to like an electric fuel pump sound, or a relay in a sort. I didn’t get to finish the procedure I’ll try again later I had to go do something. Maybe my iac is plugged up. And last time I did the codes from flashes there was none but I’ll check them again just incase.

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Just saw your other posts. Your idle should not whatsoever need to be touched, you have a vacuum leak or a IAC that is failing or sticking. YOu should take it off and clean it.

How would I go about cleaning it? I assume unplug and use adjustable wrench to remove but what should I clean it with?

iamtherealJayy said:

How would I go about cleaning it? I assume unplug and use adjustable wrench to remove but what should I clean it with?

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carb spray only on the metal parts and a tooth brush. Idk what the TBI ones look like

I just looked it up. If it is indeed just like this like it seems to be, you probably have a bad seal on the o ring. Those things get hard after 20 some years. The pintle is probably caked in carbon so the thing cant detect its ass from its head properly. Also based on the age, its probably showing signs of wear/doesnt work the fastest anymore. They are inexpensive but if you want to try cleaning and making sure the o ring is okay first, you can, but I would get a new GM unit because of how long they last and start slipping or just take longer to react, giving a feeling of a hunting idle when the computer command was on point.

Dont let solvent get into the housing or leak down the pintle or shaft and it has a install procedure where you cant have it fully extended probably but that is based on my buick where it has to be 28 or 18 mm at most or sometihng.

Carb spray and the o ring if its brittle or flat, its prob the seal issue.

the IAC will be the threaded type and doesn't have an Oring like the picture above. unless the passage is carbon filled or the pintle has carbon build up on it, there isn't much else to clean on it.

also the OP said he sprayed carbon cleaner around the TB unit looking for vac leaks and none were apparent.

I’ll take the iac out when I get back home and check it out, I also checked the vacuum canister earlier and the lines going to it appear solid with no cracks or loose connections, although there’s a soft line sitting by the canister that has a purge valve kinda plastic end on it similar to the rear differential breather tube end. It connects to a hard line by the power steering lines, what could this be?

iamtherealJayy said:

…there’s a soft line sitting by the canister that has a purge valve kinda plastic end on it similar to the rear differential breather tube end. It connects to a hard line by the power steering lines, what could this be?

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Front diff breather.

iamtherealJayy said:

I’ll take the iac out when I get back home and check it out, I also checked the vacuum canister earlier and the lines going to it appear solid with no cracks or loose connections, although there’s a soft line sitting by the canister that has a purge valve kinda plastic end on it similar to the rear differential breather tube end. It connects to a hard line by the power steering lines, what could this be?

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you dont have a 700r4 by chance do you

iamtherealJayy said:

The throttle cable returns fully to its position with no drop in idle speed. I reckon I’ll change the thermostat to a 195 today since it is getting cold and it would be nice to have heat through winter. What should I use to clean the iac to make sure it’s clean?

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Carburetor cleaner.

Dude it will never EVER run right with a 160° thermostat installed. The computer thinks it is cold and you are stuck in OPEN LOOP.

Do you know what it is?

All energy outside of changing the thernostat is wasted in speculation.

Seriously dude the IAC likely is NOT your problem especially if it's not throwing codes, you are trying to adjust the idle speed and ignition timing with the engine in CHOKE.

It.will.not.work.
You can.not.fix it without changing thermostats. It will never ever ever run right with a 160°thermostat installed. Adjust sensors until the cows come home and it will still be in CHOKE.

Rusty Nail said:

Carburetor cleaner.

Dude it will never EVER run right with a 160° thermostat installed. The computer thinks it is cold and you are stuck in OPEN LOOP.

Do you know what it is?

All energy outside of changing the thernostat is wasted in speculation.

Seriously dude the IAC likely is NOT your problem especially if it's not throwing codes, you are trying to adjust the idle speed and ignition timing with the rngine in CHOKE.

It.will.not.work.
You can.not.fix it without changing thermostats.

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Good point. If its running cold enough, your cat isnt getting hot enough and your oxygen sensor may not either or if it is, your ECM is probably overriding because it doesnt see warm up. IT will also not want to lockup torque converter if that is electronic.

On starting mode, the ECM/PCM checks the coolant temp. sensor(CTS),throttle position sensor(TPS), manifold absolute pressure(MAP),and crank signal, then determines the proper air/fuel ratio for starting. Run mode has either open or closed loop.When the engine is first started , and it is above 400 RPM,the system goes into open loop -the ECM ignores the signal from the O2 sensor, and calculates the air/fuel ratio based on inputs from the coolant temperature and MAP sensors. The system stays in open loop until the O2 is hot enough to operate properly ,the CTS is above a specified temp, and after a specific amount of time has elapsed after starting the engine...

Respectfully, these guys saying coolant temp isnt "a big deal" are wrong and 100% incorrect.
It is a cornerstone of proper engine function and the foundation upon which all other adjustments are calculated.

the system will still hit closed loop with a 160deg thermostat. my thermostat was partially stuck open recently. it was basically was functioning as a 160 degreee thermostat per ALDLDROID ecm temp reading. I still hit closed loop and the engine ran fine....I was just burning more fuel than I needed to and the heater was weak.

if the OP is SURE there are no vacuum leaks and all the other sensors are working, the issue is very likely the IAC. it is either partially stuck open by carbon deposits, needs to be reset, or needs to be replaced.

I’m going to change the thermostat to a 195, it didn’t have one when I first got it. Previous owner said ran hot(was lower rad hose) and oreillys recommended a 180 for my area since it’s hot in the south, ran that for a while until it started running hotter so I just threw a 160 in it to keep it cooler during the hot weather but it’s averaging 35° now and 160 isn’t providing good enough heat on my feet. So I’m going to start with changing it regardless. But it most definitely is more than just the thermostat because it idles high even with the 180.

Not a 700r4 it’s an sm465 L123R manual tranny, was driving home in third gear going about 50 at around 1600 rpm pushed clutch in to downshift to second and it shot up to 2000, few people have told me that’s just the emissions and smog stuff on the tbi “keeping clean” I don’t think it should rev that high tho even if that is what it’s doing.