Help Engine idle speed and stalling

[westcasey]

I need help! I have a GMC R1500 throttle body injected pickup. I have had it in the shop several times. The thing keeps stalling when you put it into gear. The mechanic drilled out the idle adjust screw and moved it around. Turned it up way too high. Now I have a guy that is trying to solve the problem instead of cover it up and we can't find what the original engine idle speed is supposed to be.

With the timing set dead on what its supposed to be the truck pings on acceleration dies when you put it in gear. The EGR valve has been replaced; there are no vacuum leaks. Knock sensor is working correctly. What else could this be?? Its been hooked up to the computer and everything passes.

Would appreciate any possible suggestions.

[lurch115]

i would check 2 things....one that the harmonic balancer isn't worn out as i have seen several of them where the outter ring slips and so if you set the timing by it....it will be wrong....the other thing to check could me that the passager side center 2 cylinders have the spark plug wires switched around...they are close enough in the firing order that you wouldn't notice it all the time....but they will make a difference

[Captkaos]

Originally Posted by westcasey

I need help! I have a GMC R1500 throttle body injected pickup. I have had it in the shop several times. The thing keeps stalling when you put it into gear. The mechanic drilled out the idle adjust screw and moved it around. Turned it up way too high. Now I have a guy that is trying to solve the problem instead of cover it up and we can't find what the original engine idle speed is supposed to be.

With the timing set dead on what its supposed to be the truck pings on acceleration dies when you put it in gear. The EGR valve has been replaced; there are no vacuum leaks. Knock sensor is working correctly. What else could this be?? Its been hooked up to the computer and everything passes.

Would appreciate any possible suggestions.

That ain't the way to fix it... I just went through this and documented it here, I was baffled as there was several contributing factors (370K miles and it sat in a field for 2 years): http://forum.73-87chevytrucks.com/sm...p?topic=3984.0

Things to check.
A)Fuel pressure = must be 10-13lbs.
B)Injectors firing correctly = put a timing light on any plug and shine it toward the injectors (may need a dial-back to see) they should fire when the spark fires.
C)spray pattern of the injectors.
D)pull the IAC out (engine off) and see if it is gummed up? they can be cleaned.

Since someone monkeyed with the idle, I would run the screw back to where the blades are closed but resting on the stop, not the throttle bores.

[lurch115]

hmmm....i forgot all about the IAC valve...and i bet that is the problem too...i had a '90 Caprice with a 350 vortec in it and it did the same as his is doing....replaced the IAC valve and it was cured......



P.S. don't change the valve in the parts store parking lot. i did that and the car idled at 1,500 rpms all the way home...ya have to unhook the battery for 30 minutes to reset the computer

[turbojunker]

Originally Posted by Captkaos

That ain't the way to fix it... I just went through this and documented it here, I was baffled as there was several contributing factors (370K miles and it sat in a field for 2 years): http://forum.73-87chevytrucks.com/sm...p?topic=3984.0

Things to check.
A)Fuel pressure = must be 10-13lbs.
B)Injectors firing correctly = put a timing light on any plug and shine it toward the injectors (may need a dial-back to see) they should fire when the spark fires.
C)spray pattern of the injectors.
D)pull the IAC out (engine off) and see if it is gummed up? they can be cleaned.

Since someone monkeyed with the idle, I would run the screw back to where the blades are closed but resting on the stop, not the throttle bores.

That was a good thread, I have an 82 C20 with an 87 TBI 350/700R4 in it that is doing the exact same thing. I needed some more ideas.

[Captkaos]

Originally Posted by turbojunker

That was a good thread, I have an 82 C20 with an 87 TBI 350/700R4 in it that is doing the exact same thing. I needed some more ideas.

I am in Birmingham also. shoot me an email or post on either board. I am glad it helped someone. It was driving me nuts.

[westcasey]

Haven't had time to check it out yet. Thanks for the hints. Today though it has started crankng and cranking and not firing. Takes a long time to get it started. Am wondering if it isn't the fuel pump. Will let you all know when I get a chance to go through it.

[grinch4om]

IAC will do just that. when its cranking, crack the throttle just a little as this will be mimicking the function of the IAC. if it starts, replace the IAC

[Farmer Mike]

Here are a couple of ideas. Clean the IAC and adjust it...

1.)Drill out the pressed in cap over the adjustment screw and obtain the proper torx screw driver (done)
2.)Warm up the truck and shut it off
3.)Jumper A-B on the ALDL connector
4.)Wait 30 seconds while the IAC closes
5.)Remove the IAC connector on the TBI
6.)Start the truck
7.)Adjust the idle speed to 600 rpm
8.)Shut-off the truck
9.)Reconnect the IAC and remove the jumper.

Did you disconnect the tan/black wire before timing it?

Make sure your fuel filter is good (if you can't remember the last time you did it, then it's time)

Do you get any trouble codes? (jumper A-B on the ALDL and count the pulses on the SES)

The link in one of Captkaos post's give some great troubleshooting info!

Good luck!

[westcasey]

Farmer Mike,

I'll try that when I get time; I'm leaving town for a couple weeks. Is the idle @ 600 rpm in park w/ the A/C off?

[Farmer Mike]

Maybe not @600RPM in park. I've always tuned mine for 650RPM in drive. Monitor your RPM drop when in gear and go from there (~850RPM in park with A/C off).