94 K1500 Idle Surge

Impulse · 12-02-2008, 05:36 PM

Hey guys. I'm new to this board and have a bit of an annoying problem.
I have a 94 K1500 with the v6. It has a random idle surge problem.
The problem is not limited to the truck being warm or cold. It happens randomly.

What's been done:

Obviously a full tuneup, gas treatment, new plugs, wires, etc.

The truck has been taken to a shop which determined that the timing was off a tooth. They corrected the timing and cleaned the EGR valve. Returned the truck and said there was nothing else wrong with it... It was at this point that I lost all faith in shops and decided I am more mechanically inclined.

Intake gasket was replaced. No change.

I found six or seven vacume leaks, all near/going to the EGR Solenoid. No effect on the surge. There were no other vacume leaks.

I replaced the cold air idle motor and that had no effect either, and the truck still surges.

Is there anyway to blockoff the EGR completely to eliminate it from things im looking at? I don't need to pass emissions here in upstate NY.

My next guess would be the ECU, EGR valve, EGR Solenoid, or FIAV(Fast Idle Air Valve). I don't know if this truck even has an FIAV though....

Any help would be greatly appreciated!

PS: Truck has a sparratic CEL, not when the car idle surges, but not when it doesn't... IE doesn't SEEM to be related even though I'm sure it is.

dave8590 · 12-02-2008, 06:13 PM

um... not sure seems like youve tried every thing... but welcome anyways!

cburcham73 · 12-02-2008, 06:27 PM

try pulling the codes. if your cel blinked it is stored.blocking off your egr valve would not be the best thing to do. check your voltage at your iac motor and see it the ecm is controlling it.

Impulse · 12-02-2008, 06:30 PM

I know the ECM is controlling it because unplugged the car idles at 2500rpm.
What about the injectors? Possible that they're dirty or clogged?

cburcham73 · 12-02-2008, 06:45 PM

injectors wouldnt cause a random surge.it would cause a miss alot. unless you have a injector coil heating up and its intermiting.
[by the way} how were you a tooth off in timing? did someone else mess with it before you got it?

Impulse · 12-02-2008, 06:47 PM

Its actually a friend of mines truck. Like I said, it ended up in some shop and he was told it was off, and the truck was retimed.

Does this truck have an FIAV?

gmctrucks · 12-02-2008, 07:35 PM

My 87 Suburban would do that every some often it was the TPS sensor. Hey why don't you do the Seafoam dealy look at video below the stuff cleans the whole upper intake and injectors.
YouTube - Seafoaming After you add Seafoam and you let the engine die let sit for 30 minutes then turn on the car pour the rest of the can into gas tank.

Impulse · 12-02-2008, 08:09 PM

I'm confused as how the TPS sensor would effect the car at idle? As long as it's reading CLOSE to 0% there shouldn't be a problem... The only thing I can think of is that you wouldn't be getting constant voltage and it'd be fluctuating, but I don't think that that would stall the truck out etc.

Do they have to be dialed in or can I just drop a new TPS in the truck?

I'll seafoam at the next opportunity.

cburcham73 · 12-03-2008, 05:04 AM

you have to test the tps. back probe the wires with your volt meter,run your throttle up and watch your meter. if it skips during your throttle stroke then the tps is bad. you should have a constant reading from closed to wot. this skipping in your tps will **** off your ecm and make your truck run like ****.

leolkfrm · 12-03-2008, 06:36 AM

Actually, the egr must be present for inspection if it was there when built. You don't need the computer read like 96 and later.
You need a scan with a good scanner not a code reader, Are you in upstate as in western or up the northway?

12-02-2008, 05:36 PM	#1
Impulse Full Member Join Date: Dec 2008 Posts: 10	94 K1500 Idle Surge Hey guys. I'm new to this board and have a bit of an annoying problem. I have a 94 K1500 with the v6. It has a random idle surge problem. The problem is not limited to the truck being warm or cold. It happens randomly. What's been done: Obviously a full tuneup, gas treatment, new plugs, wires, etc. The truck has been taken to a shop which determined that the timing was off a tooth. They corrected the timing and cleaned the EGR valve. Returned the truck and said there was nothing else wrong with it... It was at this point that I lost all faith in shops and decided I am more mechanically inclined. Intake gasket was replaced. No change. I found six or seven vacume leaks, all near/going to the EGR Solenoid. No effect on the surge. There were no other vacume leaks. I replaced the cold air idle motor and that had no effect either, and the truck still surges. Is there anyway to blockoff the EGR completely to eliminate it from things im looking at? I don't need to pass emissions here in upstate NY. My next guess would be the ECU, EGR valve, EGR Solenoid, or FIAV(Fast Idle Air Valve). I don't know if this truck even has an FIAV though.... Any help would be greatly appreciated! PS: Truck has a sparratic CEL, not when the car idle surges, but not when it doesn't... IE doesn't SEEM to be related even though I'm sure it is.

12-03-2008, 06:36 AM	#10
leolkfrm Senior Member Join Date: Mar 2008 Location: N.Y. Posts: 4,300	Actually, the egr must be present for inspection if it was there when built. You don't need the computer read like 96 and later. You need a scan with a good scanner not a code reader, Are you in upstate as in western or up the northway? __________________ 4 wheels move the body 2 wheels move the soul B.W.A.I

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12-02-2008, 06:13 PM	#2
dave8590 Senior Member Join Date: Oct 2008 Location: orland park ill. Posts: 143	um... not sure seems like youve tried every thing... but welcome anyways!

12-02-2008, 06:27 PM	#3
cburcham73 Senior Member Join Date: Aug 2008 Location: williamsburg virginia Posts: 183	try pulling the codes. if your cel blinked it is stored.blocking off your egr valve would not be the best thing to do. check your voltage at your iac motor and see it the ecm is controlling it.

12-02-2008, 06:30 PM	#4
Impulse Full Member Join Date: Dec 2008 Posts: 10	I know the ECM is controlling it because unplugged the car idles at 2500rpm. What about the injectors? Possible that they're dirty or clogged?

12-02-2008, 06:45 PM	#5
cburcham73 Senior Member Join Date: Aug 2008 Location: williamsburg virginia Posts: 183	injectors wouldnt cause a random surge.it would cause a miss alot. unless you have a injector coil heating up and its intermiting. [by the way} how were you a tooth off in timing? did someone else mess with it before you got it?

12-02-2008, 06:47 PM	#6
Impulse Full Member Join Date: Dec 2008 Posts: 10	Its actually a friend of mines truck. Like I said, it ended up in some shop and he was told it was off, and the truck was retimed. Does this truck have an FIAV?

12-02-2008, 07:35 PM	#7
gmctrucks Senior Member Join Date: Nov 2006 Location: Houston,Texas Posts: 4,035	My 87 Suburban would do that every some often it was the TPS sensor. Hey why don't you do the Seafoam dealy look at video below the stuff cleans the whole upper intake and injectors. YouTube - Seafoaming After you add Seafoam and you let the engine die let sit for 30 minutes then turn on the car pour the rest of the can into gas tank.

12-02-2008, 08:09 PM	#8
Impulse Full Member Join Date: Dec 2008 Posts: 10	I'm confused as how the TPS sensor would effect the car at idle? As long as it's reading CLOSE to 0% there shouldn't be a problem... The only thing I can think of is that you wouldn't be getting constant voltage and it'd be fluctuating, but I don't think that that would stall the truck out etc. Do they have to be dialed in or can I just drop a new TPS in the truck? I'll seafoam at the next opportunity.

12-03-2008, 05:04 AM	#9
cburcham73 Senior Member Join Date: Aug 2008 Location: williamsburg virginia Posts: 183	you have to test the tps. back probe the wires with your volt meter,run your throttle up and watch your meter. if it skips during your throttle stroke then the tps is bad. you should have a constant reading from closed to wot. this skipping in your tps will ** off your ecm and make your truck run like **.