check engine lamp

[diveplane]

ok guys i have a weird issue with my check engine light, mainly when the motor has heated up driven for a while , most cases its when i have stopped the check light comes on, then sometimes clears, sometimes it comes on when driving? any idea?


would a vacuum leak cause this?

[diveplane]

engine starts runs great all weather conditions.

[95 S_Trucker]

What is the year/make/model/engine/transmission? What codes are stored?

[diveplane]

1994 chevy 1500 v6 manual stick shift
W/T all factory standard no mods.


will plug up the monitor obd1 tool and take screens

[sntrym95]

The CEL will come on periodically if there is a code stored. Just a guess but it's probably EGR related, and the subsequent times it comes on is just the stored code. Let us know what code(s) you get and go from there.

[diveplane]

let me get back to you guys on this in a few days ..thx for the support great community here.

[diveplane]

ok i turned on my obd1 reader via phone bluetooth

maybe some of u guys can decode what all this means


says my truck is idling little to high any idea what sensor controls that?

[diveplane]

few more screens of the ALDL

[diveplane]

..

[diveplane]

try to do the old school method as well and short paper clip across A and B terminals see what codes are stored.

[sntrym95]

Idle might be a tad high because the engine isn't fully warm yet, even though it's in closed loop.

Code 35 looks to be set, which is the IAC. You might be able to remove it and clean it, but be careful not to let the pintle and spring fall out. Or just get a new one.

[diveplane]

ok can u post a pic of this up bud and approx price for a new one?

what does it control?

[sntrym95]

IAC = Idle Air Control Valve. Controls the idle mixture to get idle rpm to the desired number. ACDelco runs about $100. Aftermarket ones from big auto part stores run cheaper but generally the quality sucks.

See if you can get a Standard brand, they make a lot of the OEM stuff anyway. http://www.standardbrand.com/en/prod...rol-iac-valve/

If you want to try and clean it, there are some posts about that here on the board.

[ChevyTech]

The light is coming on because of the IAC trouble code.
The IAC position is at zero in your data and the engine is above the desired RPM.
Either the IAC or its wiring has failed so it will not close when sent pulses by the computer or the engine has a vacuum leak.

A common vacuum leak on these trucks is the gasket that is right under TBI unit.

You can look down the passenger rear corner of the TBI unit and see the IAC plunger to see if it looks like it has a the passage closed. If the IAC is truly fully extended and has the passage fully closed off and the engine is running at 700 RPM then there is a vacuum leak somewhere.

[diveplane]

Originally Posted by sntrym95

Idle might be a tad high because the engine isn't fully warm yet, even though it's in closed loop.

Code 35 looks to be set, which is the IAC. You might be able to remove it and clean it, but be careful not to let the pintle and spring fall out. Or just get a new one.

yea am getting a code 35 and 44 guys shorted pins a and b

[diveplane]

Originally Posted by ChevyTech

The light is coming on because of the IAC trouble code.
The IAC position is at zero in your data and the engine is above the desired RPM.
Either the IAC or its wiring has failed so it will not close when sent pulses by the computer or the engine has a vacuum leak.

A common vacuum leak on these trucks is the gasket that is right under TBI unit.

You can look down the passenger rear corner of the TBI unit and see the IAC plunger to see if it looks like it has a the passage closed. If the IAC is truly fully extended and has the passage fully closed off and the engine is running at 700 RPM then there is a vacuum leak somewhere.

ok i checked for a possible internal manifold leak while engine was running i removed oil cap no suction , good sign ..

the code 44 lean mixture reading would be from? i checked asdl again and the o2 sensor is fluctuating voltage which tells me its operating ok.

i did notice when ignition was to the on position the IAC read a reading steady voltage , then when truck fired up it reads 0 no voltage fluctuation ,tells me its non functioning.


can the IAC be removed and tip cleaned with carb cleaner?
and spray inside tbi housing for it?, if this fails a new IAC could be the fix.


whats the procedure for vac lines outside can u use carb cleaner along lines?
if engine rpms alter that's where the leak is? correct?

is it safe to use while engine is cool?

any other alternative to vac check lines?

[diveplane]

here's the reading with just ignition on as u can see the IAC reads a output but once motor runs it reads 0

[95 S_Trucker]

IAC at 0 and a lean code. There is a vacuum leak. Intake manifold gasket, throttle body gasket, any vacuum line are possible causes.

[sntrym95]

^^I second the vacuum leak. The IAC is likely not the issue. The leak is very small as it's only 50 rpm above normal, so it could be tough to track down. I would check all of the vacuum hoses for cracks.

[rpmerf]

Since you got that fancy tool, you might be able to pull the vac lines off one at a time and block off the port with a cap or your finger to see how it reacts. If the speed drops to the desired level, you found your leak.

You can use carb cleaner to find the leak. Watch the A/F and engine speed for a spike. Be sure to spray around the base of the throttle body and the intake ports at the intake gaskets.

[diveplane]

can i use my propane torch gas on valve on off no flame of course, i herd its safer to use.

[diveplane]

Originally Posted by sntrym95

^^I second the vacuum leak. The IAC is likely not the issue. The leak is very small as it's only 50 rpm above normal, so it could be tough to track down. I would check all of the vacuum hoses for cracks.

think i will invest in a mechanics stethoscope.

[rpmerf]

stethoscope may work. You can use a piece of vacuum line in one ear and cover the other or use an ear plug.

Propane should work. Watch A/F and RPM, listen for sound changes.

[diveplane]

safest method i think might be using spray mist water would this work guys?
long as i keep it away from electrical behind tbi


if i find leak with water it will reduce rpms? right

[speedygonzales]

First, the leak is not small if the IAC is at 0. Unless the IAC is stuck open.

Second the leak is not likely at the intake ports since there does NOT appear to be a single misfire. This would indicate the leak is common to all cylinders.

Which brings us back to what Chevy Tech said about the TB gasket being a problem with those engines. He also told you how to see if the IAC was indeed actually closed visually.

So to repeat what you were told, look for the pintle on the IAC. If it's there, spray something like WD40 around the base of the TB. If the RPM's drop, you found the leak.

If the IAC is not closed, you have to find out why. Is it loss of signal from a wiring issue or is it blocked with debris or is it bad.

Got it now?