Why You Shouldn't Adjust the Idle of your Chevy TBI

I thought the idle was low. I had not tools or experience to tell me this. But the car died once when I was slowing down, so I thought I'd try it out. THIS IS NOT SOMETHING TO JUST TRY OUT!

[@wandajames6234]

Retired Class A tech here. There is a reason those idle screws are sealed-- because you will be messing with a delicate balance of sensors. And you will likely have ongoing issues if you do mess with it. Better to find the underlying problem. A manual is a big help. RESEARCH. Start with the simplest jobs first-- is the air filter clean; get some spray sensor cleaner and clean the MAF and MAP sensors and whatever other sensors that can be cleaned; clean the throttle body with TBI spray cleaner; check condition of vacuum hoses-- put your ear down, sometimes you can hear a hissing if there's a leak; the EGR Valve is very important- mechanical ones can be removed and the little pintle valve inside freed up-- you can test if it holds vacuum with a basic vacuum tester- or just get a new one if it's original and old. Research how to inspect and test the Idle Air Control valve and TPS; then you can start getting into the bigger things like fuel pressure tests, O2 sensor test, pulling the throttle body and check injectors and the gaskets and of course you will need to replace them as they get damaged upon removal. It's always about getting enough air, fuel and spark as well as having clear exhaust channels. There cannot be any fuel, air or electrical system (arcing) leaks. Just go at it systematically. Sometimes it is the simplest thing. You should invest in: a multimeter; a vacuum tester; possibly a fuel pressure gauge, and hopefully a comprehensive manual for your model which will have all the specs and electrical diagrams you need. It will also show how to bring up codes and what they mean. Invaluable. No guessing. Haynes, Chilton-- can get them used.

[@kuklok1989]

They were capped off for smog purposes

[@johnnysalazar1552]

You da man did wat you said runs great

[@TravisJenson-zv9lz]

Agreed i feel the same way , but i refuse to let a manufacturer govern my ability to make adjustments and experiment with different trims after all i paid for it and am completely fine with the possibility i may cost myself yet again to straighten out anything i ruin, thats the fun of ownership and making mistakes and learning 🤙 the original designer of them rochester units intended them to be adjustable for great reason , motor parts wear out just like human body parts, what was a perfect setting when vehicle was brand new is not gonna be the same after even fifty thousand miles…

[@kCI251]

@@TravisJenson-zv9lz The caps are to make sure you don't fool with it under warranty.

[@etmesi]

A lot was wrong with my 1992 GMC from faulty Mechanics, but I even thought of adjusting the idle because it idles so low almost stall. I changed every sencer in the truck, one made a difference was the Knock Sensor, that one one module I missed. Knowing the truck is old and I know modules run off the engine block ground, I got an extra ground cable and installed a second ground, that seemed to add horsepower. After suffering with a bad running engine for 8 years, tonight was the first time in years feels like a 100 more HP was added to in. In the TBI rebuild I installed the POD spacer and intake TBI spacer that woke the engine up, does work.

[@jf4872]

No hole in the side. You should have taken the TBI off and center drilled with roughly 3/16 drill the metal cap you see (carefully). Once out you'll see the screw. But if you're having an idle issue it is likely a vacuum leak at the TBI base and/or the throttle shaft ends. You also need to verify fuel pressure (critical) before anything else.

[@stevejohnson6696]

And I've adjusted mine up and down whenever needed and it runs perfect I don't have to leave it where the factory said it at all

[@svendhellested3463]

I have the same high idle situation. Changed my IAC valve 3 yrs ago to pass smog. It worked then, but in winter it takes forever to idle down. Im a proffesional heavy equipment mechanic. Not TBI expert. Lets start with basics. The ECM uses the IAC to control idle. If the IAC is sticky it will be slow to idle down like mine. So first thing is to make sure engine is coming to temperature. Mine does but takes a long time in winter. Factory guages are not accurate. Use an infrared gun to ck temp at thermostat housing. If it dont reach 195, replace thermostat. If it does, then the trick with the wire will put it in base mode. That the reset mode, and keep it there. At that point the IAC should be closed. If the idle is ok, then the IAC or the Coolant Sensor that reads temp are at fault. Im going to try the wire jump tomorrow. That will tell me if the coolant temp, sender, or IAC are possible. Last resort is throttle adjust. In my case my temp guage is reading only about 1/3. So I really suspect the cooling is the issue. I put a double core radiator in. And I usually drill a very small pin hole in the thermostat to make filling easier. The other test option is to put a blanket over the radiator and let the temo guage get to say just below the red, and see if it idles down.

[@benofalltrades]

Thanks for that I'll have to give this a shot

[@cecilsabourin9462]

Check out the manual to easily reset the IAC before going into these gymnastics . I just replaced my IAC and trusted the manual and it worked great ,now idling at 600 rpm s, no sweat ,6 minutes later. , and I knew nothing about the system. Just saying.

[@stoker20]

I had to turn my screw in to raise the idle. After 448K miles there was wear on the tip of the screw and it had also pounded into the throttle body.

[@vtwinironhorse]

91 G20 sportvan . It took a minute but I finally got mine running smooth as silk panties. Full custom van so I'm familiar with silk panties. Here kitty kitty

[@user-qd1hx3fs1r]

New tbi for you!

[@joeywalton3681]

You have to also adjust the throttle position sensor when you adjust the idle. I would also recommend unplugging the battery for an hour. Good luck and best wishes! J

[@cecilsabourin9462]

You know what. The manual will tell u,exactly how to do this, no TPS adjustment needed. After installing AIC,leave plugged in. Turn key to On position ( don,t start ) for 10 seconds. Then Off for 10 seconds ( to reset the valve ) . Restart motor for 5 minutes at idle . Shut Off for 30 seconds . Restart motor and observe rpm s . Mine is app. 600 rpm s ( per dash tach ) Runs much better ,runs faster than before without bogging and smother. !992 K 1500-350

[@sergiomslacara2214]

Creo que no necesitabas perforar el tbi, ese tornillo no lo debes mover, ese es el ralenti de base del motos, debes de buscar primero otra falla, ahora tienes que volver a poner el ralenti de base, pero con un scaner. Depende del año de la chevy, saludos

[@soupflood]

If you will adjust the throttle idle screw, shouldn't you permanently disconnect the IAC valve after resetting (closing) it? Don't know if and how the TPS can be adjusted after that though.

[@jf4872]

Yes. It's referred to as 'Setting min idle speed'. It's done with the IAC seated (closed) fully and unplugged at normal operating temp 195+. You generally do not need to mess with the factory set screw. If you have an idle issue it is very likely a vacuum leak at the TBI base gasket and/or the throttle shaft or fuel delivery issue. When it comes to TBI issue/s always confirm fuel pressure before anything else.

[@soupflood]

@@jf4872 that, or the fuel pressure may be low. Happened to me, you may laugh, but I had less than two gallons of gasoline in the tank and the engine didn't even want to start. I could _see_ the injectors spitting out gasoline, but what you see is not always what you get. I thought the diy ECU I installed was to blame, modified various constants... Issue was still there. Dumped a gallon and it started but didn't want to accelerate. Another gallon and it accelerates... okay. I guess it needs yet another gallon in there.

[@jf4872]

@@soupflood Absolutely agree. With the TBI system fuel pressure is very much one of the first things one should check. Low pressure can cause surging (lean condition).

[@stevejohnson6696]

I removed my plug and I sure didn't drill on anything are go through half of or go through half of the stuff you have gone through mine came out fairly easy

[@marshallthayer7821]

Did you figure it out? I replaced my iac and have the same problem that it runs like turd.

[@benofalltrades]

Not yet, still giving me issues. It sat all winter and I'm looking for a mechanic to take it to. Hard to find for these trucks

[@ThomasMealerJr]

Why are you using a drill bit so cheap that it'll bend?

[@justind947]

I am having having the same issue with mine idling. Replaced fuel pump, injectors, idle air control valve, throttle body, coil, Spark plug wires, Spark plugs, distributor, plugged evap leaks, had a shop rebuild the motor. It still doesn't work right.

[@benofalltrades]

Yeah these trucks are hard to diagnose. I wish I knew more about how to help. On mine I also replaced the ignition control module, throttle position sensor, o2 sensor, and vehicle speed sensor. I've been told the egr could cause issues as well, but I never replaced it

[@nayrkriegdouch7989]

Check Map sensor, fuel filter, fuel pressure regulator

[@howardiko7156]

I am kind of thinking your throttle plates have varnish and soot from fuel boil after the engine is stopped.

[@benofalltrades]

What can I do to fix that?

[@fgoindarkg]

Carb cleaner

[@jackbnmbl7]

That sticker is not hidden. It's in plain sight. I don't know why you didn't drill a small hole in the cap, turn a screw into the hole, pull the cap out with a vicegrip.

[@gmccrarygm]

I did this years ago...very simple...no different than removing the air mixture screws from an old quadrajet carb

[@vtwinironhorse]

Operation CHARM : car repair manuals for everyone

[@cfellows77]

I’m having same issue. It was bogging down when put in gear so I replaced the IAC and now it’s struggling to even start. I’ve done all the things you did in this video and still having the issue 😢

[@benofalltrades]

Yeah I still can't get my truck to run right. . I don't know what else to do to it

[@jesusrodriguez6566]

Reiniciar

[@cfellows77]

@@jesusrodriguez6566 huh?

[@larrycobb3102]

I had to replace the ICM meaning Ignition control module too get my truck running. My truck is a 91 gmc with 5.7 350 TBI engine.

[@ChillkootMarkowee]

I did that on a 1989 Chevy Van G20 with the 350 TBI, because it wouldn't stay running idling below 1500rpms! It must have a computer problem or something! As I've also worked on a 1991 Chevy Step Van P30 with the 350 TBI, except it can idle as low as 400rpms and not stall at all.

[@robertfisch4603]

Fuel pressure valve. They make an adjustable after the market modification. There's vedios showing the rebuild and mods.

[@ChillkootMarkowee]

@@robertfisch4603thanks for the info! Actually I managed to figure it out after the van died and and lost spark! It turns out the original distributor, the magnetic timing pick up wheel seized and the distributor shaft was still turning! A new complete distributor solved the problem. It idles at 500rpms all day long no problems.

[@robertfisch4603]

@@ChillkootMarkowee happy you found a cure. Sometimes you just have to drive them till they break completely to get to the bottom of the problem. Lol.

[@ChillkootMarkowee]

@@robertfisch4603 yeah I know holy crap, what a head scratcher!

[@Sirjayden2000]

I adjusted my '90 5.7L TBI (my idle was always 1000-1500rpm before) and no matter how many turns on the idle screw, it made zero difference to my idle rpm. Didn't change fuel economy either, still runs on 9 mpg and spite for my attempts to improve it 😂

[@benofalltrades]

Guess those old computers actually did something. That's a tough mpg to live with!

[@juanyiste9032]

Amigo como solucionaste..?

[@Samtrucker52]

I drilled mine No issues

[@elcabo7597]

What was wrong with urs?

[@coldonehernandez4906]

Check fuel pressure, that’s critical on tbi

[@stoker20]

How do you check the fuel pressure coming from the regulator???

[@Dad2ADaughter_Cpt_Blakesbeard]

Lmao. Should just lowered the radiator hose. Then drilled through the center of the seal. Geez

[@Impala-qp9cb]

Check your throttle shaft play. As it wears out it wallows the holes vacuum leaks and misaligned throttle plates

[@barrygordon1173]

Yeah you dont drill side of throttle the plug is tin...throttle is cast aluminum...second you dont pull out the A and B....and need some sort of tach to adjust...base idle is 540 rpm to 570 rpm....

[@adenseay7406]

How do you remove plug then

[@cecilsabourin9462]

@@adenseay7406 Read the manual first, u won,t believe how quick and easy it realy is

[@adenseay7406]

@@cecilsabourin9462 can you sum it up for me

[@jf4872]

@@adenseay7406 TBI off the engine and use a 3/16 drill and carefully remove the cover. But before you do that check for vacuum leak/s at TBI base and throttle shaft ends. Also verify fuel pressure first before anything (critical).

[@barrygordon1173]

@@adenseay7406 drill it...

[@JoeBattle]

On these TBI motors, the sensors and proper spark are always the issue. I've got a 95 K-1500 and my idle went goofy up and down for a while then got worse. Changed out the TPI sensor, MAP sensor, IAC sensor and it got a bit better then got worse. Changed plugs, wires, Cap and rotor and everything is like brand new and running smooth as silk. All of these things work together to make these engines run properly. Sometimes you think it's this but the whole time it was that. Keep all that working and up to date and you will be happy about your motor.

[@Impala-qp9cb]

Also get a multimeter on your TPS. There is a spec

[@isaacsanchez8203]

If it is a 92 or older it will never run smooth. In 93 a balance shaft was added to the engine to make it run smoother

[@mikemorgan4433]

Bullshit

[@bmore8857]

92's have balanced shaft as well

[@Impala-qp9cb]

Beg to differ. All tbi vehicles were smooth runners

[@derekgriffith4324]

Had a 90 camaro tbi. Ran like a sewing machine

[@Impala-qp9cb]

@@derekgriffith4324 dad had a 91 Silverado off showroom floor. Ran like a Swiss watch. My 90k5 with 187k on original motor does too

[@randywl8925]

How can you adjust the idle with the engine off?

[@benofalltrades]

I didn't? And you probably can't? I dunno stuff

[@randywl8925]

@@benofalltrades How do you know, maybe I have. 😁

[@robertmethia7080]

if your not recommended to due this then why are you showing this to people?

[@benofalltrades]

So people don't make the same mistake

[@derekgriffith4324]

I think what we have here is someone who absolutely no business attempting mechanics

[@justinatwood8728]

"here are the instructions" *then proceeds to not follow the instructions*

[@gwalker5327]

Yikes. This video was not content to be simply worthless, but goes above and beyond to show you how to waste a bunch of time and make things worse.