Need help with an 88 TBI 350. IAC Problem - Pirate4x4.Com : 4x4 and Off-Road Forum

dt5150 · 02-17-2011, 11:10 AM

for some reason, the IAC on it keeps going in and out. sometimes it'll work, sometimes it won't. tried a new IAC, another computer, and the wiring checks out good. even with the new IAC and computer it does the same thing. works for a while, stops working, then it starts working again. anyone have any ideas why?

adam765 · 02-17-2011, 05:19 PM

possible vacuum leak or fuel pressure issue if your wiring checks out and you put on a new IAC valve and computer

dt5150 · 02-18-2011, 07:05 AM

smoke tested the motor for vac leaks, none found. fuel pressure is consistant at 15 psi.

i have a feeling it may be something loose in the connector, in the wiring harness. it's a new harness though, from howell, so it "should" be good. but that's really the only thing that makes any sense since it does it with a new iac and new ecm. i'm thinking it's some type of intermittent connection maybe?

adam765 · 02-18-2011, 09:08 AM

time to bust out the volt meter reader and do some probing

dt5150 · 02-21-2011, 07:06 AM

yup, did a little this weekend. couldn't find anything intermittent. this is weird...

383K5 · 02-21-2011, 07:15 AM

Check to see if a pin is pushed back on the harness.

dt5150 · 02-21-2011, 07:16 AM

good idea.. i'll check.

MrWillys · 02-21-2011, 07:56 AM

Grounds, or lack there of, can cause gremlins. Is there a complete ground path between the body, frame, and engine?

dt5150 · 02-21-2011, 08:01 AM

grounding should be adequate. grounding straps from the motor to the frame, body mounted/grounded to the frame. any others i might be missing?

Bubba_Jeep · 02-21-2011, 10:18 AM

Engine grounds to ECM? There are a couple of common ground points at front of the engine that have 2-3 ground wires each, that go back to the ECM. Also, just because the wires "look" good, doesn't mean they are electrically good. If I were chasing the problem you describe, I'd remove each ground, and properly clean and reinstall it. Your problem sounds like wiring.

dt5150 · 02-21-2011, 10:22 AM

i will certainly do that. thanks for the suggestion.

rokcrawlr1 · 02-21-2011, 03:02 PM

Although there are ground straps as mentioned, you should check your grounds at the t stat housing. Mine were corroded underneath but seemed to be fine visually and cost me a lot of time doing pin outs, and trying known good parts.

dt5150 · 02-22-2011, 06:14 AM

i'll check em, thanks for the tip.

i appreciate all the tips guys, thank you.

02-17-2011, 11:10 AM	#1 (permalink)
dt5150 Registered User Join Date: Jul 2007 Member # 95938 Posts: 243	Need help with an 88 TBI 350. IAC Problem for some reason, the IAC on it keeps going in and out. sometimes it'll work, sometimes it won't. tried a new IAC, another computer, and the wiring checks out good. even with the new IAC and computer it does the same thing. works for a while, stops working, then it starts working again. anyone have any ideas why?

02-17-2011, 05:19 PM	#2 (permalink)
adam765 Registered User Join Date: Aug 2009 Member # 139990 Location: Central IN Posts: 291	possible vacuum leak or fuel pressure issue if your wiring checks out and you put on a new IAC valve and computer __________________ trucks are built, maintained, repaired by humans, you are a human you can do anything

02-18-2011, 09:08 AM	#4 (permalink)
adam765 Registered User Join Date: Aug 2009 Member # 139990 Location: Central IN Posts: 291	time to bust out the volt meter reader and do some probing __________________ trucks are built, maintained, repaired by humans, you are a human you can do anything

02-21-2011, 07:15 AM	#6 (permalink)
383K5 Registered User Join Date: Mar 2007 Member # 87934 Location: Rocinsaw Posts: 164	Check to see if a pin is pushed back on the harness. __________________ Crew Cab Build : [url]http://arkansasoff-road.com/RockCrawlers4x4/viewtopic.php?f=16&t=1234[/url]

02-21-2011, 07:56 AM	#8 (permalink)
MrWillys Registered User Join Date: Feb 2002 Member # 9991 Location: Cold Springs, NV Posts: 2,343	Grounds, or lack there of, can cause gremlins. Is there a complete ground path between the body, frame, and engine? __________________ [url]www.scotthansen.net[/url] Last edited by MrWillys; 02-21-2011 at 07:57 AM.

02-18-2011, 07:05 AM	#3 (permalink)
dt5150 Registered User Join Date: Jul 2007 Member # 95938 Posts: 243	smoke tested the motor for vac leaks, none found. fuel pressure is consistant at 15 psi. i have a feeling it may be something loose in the connector, in the wiring harness. it's a new harness though, from howell, so it "should" be good. but that's really the only thing that makes any sense since it does it with a new iac and new ecm. i'm thinking it's some type of intermittent connection maybe?

02-21-2011, 07:06 AM	#5 (permalink)
dt5150 Registered User Join Date: Jul 2007 Member # 95938 Posts: 243	yup, did a little this weekend. couldn't find anything intermittent. this is weird...

02-21-2011, 07:16 AM	#7 (permalink)
dt5150 Registered User Join Date: Jul 2007 Member # 95938 Posts: 243	good idea.. i'll check.

02-21-2011, 08:01 AM	#9 (permalink)
dt5150 Registered User Join Date: Jul 2007 Member # 95938 Posts: 243	grounding should be adequate. grounding straps from the motor to the frame, body mounted/grounded to the frame. any others i might be missing?

02-21-2011, 10:18 AM	#10 (permalink)
Bubba_Jeep Registered User Join Date: Oct 2004 Member # 37184 Location: Santa Barbara, CA Posts: 1,323	Engine grounds to ECM? There are a couple of common ground points at front of the engine that have 2-3 ground wires each, that go back to the ECM. Also, just because the wires "look" good, doesn't mean they are electrically good. If I were chasing the problem you describe, I'd remove each ground, and properly clean and reinstall it. Your problem sounds like wiring. __________________ 88XJ, Chevy 5.7L, Edelbrock MPFI, NV4500, Atlas, D44's, high steer, ARB's, 7" custom semi long-arm 3 or 4-link lift, BFG 33x12.5-15's.

02-21-2011, 10:22 AM	#11 (permalink)
dt5150 Registered User Join Date: Jul 2007 Member # 95938 Posts: 243	i will certainly do that. thanks for the suggestion.

02-21-2011, 03:02 PM	#12 (permalink)
rokcrawlr1 needs a sponsor Join Date: Mar 2010 Member # 156242 Location: OKC, OK Posts: 637	Although there are ground straps as mentioned, you should check your grounds at the t stat housing. Mine were corroded underneath but seemed to be fine visually and cost me a lot of time doing pin outs, and trying known good parts. __________________

02-22-2011, 06:14 AM	#13 (permalink)
dt5150 Registered User Join Date: Jul 2007 Member # 95938 Posts: 243	i'll check em, thanks for the tip. i appreciate all the tips guys, thank you.

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