350 Tbi Help Needed - The 1947 - Present Chevrolet & GMC Truck Message Board Network

CHEVYJEFF · 06-04-2004, 09:55 AM

My 350 tbi has a problem that has me stumped. First I am getting no ses light (no codes). What it is doing is when I go to start it (cold) like after it has sat overnight or all day at work the truck wont start unless I put the gas pedal to the floor (acts like it flooded). It will briefly fire then nothing. Hold the pedal to the floor and it will start but run rough and put out lots of black smoke. Its acting like whatever controls the increase in air flow during open loop is not functioning. After it has warmed up (closed loop) it runs great and will start every time. I guess what I need to know is what controls the increase in airflow during open loop operation and what to look for as a solution? Its getting plenty of fuel on cold start but not enough air.

Tink · 06-04-2004, 12:28 PM

Have you done a tune-up lately?

How about a throttle body rebuild?

The sensors that are used during start-up are the MAP (or MAT depending on year), the IAT, the TPS and coolantant temp sensor as well as a signal from the distrbutor.

CHEVYJEFF · 06-04-2004, 01:31 PM

I just rebuilt the motor to stock and replaced all ign components. Its definatly some sort of sensor/ control problem. I am thinking my IAC is the culprit and I am going to try and clean it. I have cleaned and rebuilt the TB but I never took the IAC motor out and cleaned it.

CHEVYJEFF · 06-04-2004, 01:57 PM

Someone check this theroy, I had the tbi off about 2 months ago and nuked it w/ carb cleaner in the parts washer w/out taking the Iac or the TPS off. I have a feeling that the carb cleaner has fubared the IAC motor causing it to be inoperative. I have also noticed that when the ac is turned on I get no idle increase. So this leads me to believe that the IAC needs replaced.
If i am not getting any codes it could mean that the electronic part of the IAC is working but the motor is not,
Any takers?

ChevyTech · 06-04-2004, 07:20 PM

Hi CHEVYJEFF
I thought I reconized the name and problem. I to visit more then one board. This one is much faster.

Quote:

Originally Posted by CHEVYJEFF

If i am not getting any codes it could mean that the electronic part of the IAC is working but the motor is not,
Any takers?

My understanding is that the computor knows if the wiring to the IAC or IAC itself is either open or shorted, but that is all. If it is electrically ok, but can not move, no code will be set.

CHEVYJEFF · 06-07-2004, 09:19 AM

(UPDATE) It was the IAC causing all my problems. Truck is running great now. Just throwing a code 43 a WOT but I will diagnose that this week. Think that its either knock sensor related or TPS need adjustment.

MD8349 · 06-08-2004, 12:55 PM

Chevyjeff, What Is A IAC And What Does IAC Stand For And How Much Does It Cost. WHERE IS IT LOCATED.

grayw0lf · 06-08-2004, 10:34 PM

Easy fix. Tear off that fuel injection computer imbedded junk & get a Holley 4bbl.

CHEVYJEFF · 06-09-2004, 01:53 PM

IAC= Idle air control valve. located on pass side of throttle body. big brass plug looking thing w/ square wire connector goint to it.

06-04-2004, 09:55 AM	#1
CHEVYJEFF Registered User Join Date: Oct 2002 Location: WYLIE TEXAS Posts: 232	350 Tbi Help Needed My 350 tbi has a problem that has me stumped. First I am getting no ses light (no codes). What it is doing is when I go to start it (cold) like after it has sat overnight or all day at work the truck wont start unless I put the gas pedal to the floor (acts like it flooded). It will briefly fire then nothing. Hold the pedal to the floor and it will start but run rough and put out lots of black smoke. Its acting like whatever controls the increase in air flow during open loop is not functioning. After it has warmed up (closed loop) it runs great and will start every time. I guess what I need to know is what controls the increase in airflow during open loop operation and what to look for as a solution? Its getting plenty of fuel on cold start but not enough air. __________________ http://members.cardomain.com/chevyjeff 57 2 DOOR HDTP 82 CORVETTE 90 V10 BLAZER 97 REGAL LSR 2100 (BOAT)

06-04-2004, 12:28 PM	#2
Tink Registered User Join Date: May 2002 Location: VA Posts: 1,337	Have you done a tune-up lately? How about a throttle body rebuild? The sensors that are used during start-up are the MAP (or MAT depending on year), the IAT, the TPS and coolantant temp sensor as well as a signal from the distrbutor. __________________ 69 Chevy C10 88 Sierra 02 2500 Suburban And too many S10s to list!

06-04-2004, 01:31 PM	#3
CHEVYJEFF Registered User Join Date: Oct 2002 Location: WYLIE TEXAS Posts: 232	I just rebuilt the motor to stock and replaced all ign components. Its definatly some sort of sensor/ control problem. I am thinking my IAC is the culprit and I am going to try and clean it. I have cleaned and rebuilt the TB but I never took the IAC motor out and cleaned it. __________________ http://members.cardomain.com/chevyjeff 57 2 DOOR HDTP 82 CORVETTE 90 V10 BLAZER 97 REGAL LSR 2100 (BOAT)

06-04-2004, 01:57 PM	#4
CHEVYJEFF Registered User Join Date: Oct 2002 Location: WYLIE TEXAS Posts: 232	Someone check this theroy, I had the tbi off about 2 months ago and nuked it w/ carb cleaner in the parts washer w/out taking the Iac or the TPS off. I have a feeling that the carb cleaner has fubared the IAC motor causing it to be inoperative. I have also noticed that when the ac is turned on I get no idle increase. So this leads me to believe that the IAC needs replaced. If i am not getting any codes it could mean that the electronic part of the IAC is working but the motor is not, Any takers? __________________ http://members.cardomain.com/chevyjeff 57 2 DOOR HDTP 82 CORVETTE 90 V10 BLAZER 97 REGAL LSR 2100 (BOAT)

06-07-2004, 09:19 AM	#6
CHEVYJEFF Registered User Join Date: Oct 2002 Location: WYLIE TEXAS Posts: 232	(UPDATE) It was the IAC causing all my problems. Truck is running great now. Just throwing a code 43 a WOT but I will diagnose that this week. Think that its either knock sensor related or TPS need adjustment. __________________ http://members.cardomain.com/chevyjeff 57 2 DOOR HDTP 82 CORVETTE 90 V10 BLAZER 97 REGAL LSR 2100 (BOAT)

06-08-2004, 12:55 PM	#7
MD8349 1999 Chevy Join Date: May 2004 Location: DALLAS, TX Posts: 61	Chevyjeff, What Is A IAC And What Does IAC Stand For And How Much Does It Cost. WHERE IS IT LOCATED. Last edited by MD8349; 06-08-2004 at 12:59 PM.

06-08-2004, 10:34 PM	#8
grayw0lf Registered User Join Date: Apr 2004 Location: Clanton, AL Posts: 1,253	Easy fix. Tear off that fuel injection computer imbedded junk & get a Holley 4bbl. __________________ 85' CUCV M1009!!! The newest addition! 6.2diesel, Th400, NP208, & only 36k miles! 70' C-10 LWB Fleetside - Looking good these days! 05' Dodge Neon 88' Winner Escape Sport 1750 - 4.3v6 94' Seadoo SP 84' Honda TRX200, bare nekkid. Just a frame & tires. Always looking for another project or any good deal!

06-09-2004, 01:53 PM	#9
CHEVYJEFF Registered User Join Date: Oct 2002 Location: WYLIE TEXAS Posts: 232	IAC= Idle air control valve. located on pass side of throttle body. big brass plug looking thing w/ square wire connector goint to it. __________________ http://members.cardomain.com/chevyjeff 57 2 DOOR HDTP 82 CORVETTE 90 V10 BLAZER 97 REGAL LSR 2100 (BOAT)



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.