'87 1/2 ton doesn't like to idle

[drumdude96]

Greetings! Brand new member here in need of some help. My old '87 Silverado 1/2 ton 2wd doesn't like to idle for some reason. It has the 5.7L TBI engine and 700R4 trans. It also runs really rough when it's cold. When I say it doesn't like to idle, it's not all the time. Sometimes it will idle okay, most of the time it seems like it's not getting quite enough fuel to idle and will die if I don't give it a little gas. If I press on the accelerator pedal very slightly, it will run just fine. A lot of the time when I am at a traffic signal, I have to give the engine a little gas as well while also holding on the brake to keep it from stalling. I've replaced a few parts here and there to try to remedy the problem, but nothing has really solved it. I put a new pickup coil in the distributor a couple years ago and that seemed to help for a while, but then the problem came back. I'm wondering if maybe it's the ignition control module or possibly even the distributor. If I remember correctly (it's been a few years), I installed a new fuel pressure regulator, TPS and IAC valve and those didn't solve the problem either. I'm just about to the point of putting a new intake and carb on it and getting rid of all the electronic crap if I can't get this figured out. Oh, and as far at the rough running when it's cold, I have replaced the coolant temp sensor and that didn't help at all. This truck is driving me nuts! Any help will be greatly appreciated!

[Katrina/10]

I have a similar problem, and tried the same things you did. No luck so far.

[J Knight]

Have you checked for any vacuum leaks?

[77chevyinline6]

Check for vaccum leaks.

[drumdude96]

Okay, I'll go ahead and just replace all the vacuum lines to see if that helps things. If nothing else, it will be an inexpensive thing that probably needs done anyway, even if it doesn't solve the problem.

[drumdude96]

Here's an update. I just went out and started my old truck and it ran beautifully. I checked for vacuum leaks and all that as well. Then I put it in gear, and it fell on its face and died. When I restarted it, it didn't want to idle at all. Often, it will run fine, then I will rev it up a bit, and then it won't idle after that, either. It also seems like the truck is running too rich. Anyone have any ideas? This is getting extremely frustrating, to say the least.

[pontgta]

Try the IAC relearn procedure posted by rfmaster..

Have some on the gas pedal until it idles when the IAC is disconnected..

http://67-72chevytrucks.com/vboard/s...d.php?t=515419

1. Install a jumper wire between Pins A & B of ALDL diagnostic connector.
2. Turn on the ignition (but don't start the engine)
3. Wait 30 seconds.
4. Leave ignition on and disconnect the IAC connector (four wire plug).
5. Remove the jumper wire from the ALDL connector.
6. Start the Engine. The engine probably will run rough and may stall. Just restart and try again.
7. Adjust the throttle stop screw to set the idle to 500 RPM +/- 50 RPM. - stock camshaft!
8. Turn the engine off and reconnect the IAC connector.
9. Turn ignition on and adjust TPS to proper settings. (0.60 - 0.65Vdc at idle is typical, but 0.3 to 0.9Vdc will work)
10. Repeat procedure until the 500 RPM +/- 50 RPM (stock cam) in step 7 can be maintained while TPS is at proper idle setting. Performance camshaft may require higher idle RPM!

Have some on the gas pedal until it idles when the IAC is disconnected.....

[Mr.Chevy4x4]

Sounds to me like your EGR is not functioning properly. I would check the EGR valve and control solenoid first. This would cause the poor idle and off idle stumble.

Mike

[Low Elco]

Crud in the EGR wil do this. Good luck!

[drumdude96]

Time for another update. I replaced the EGR valve and solenoid, and that definitely helped, but the problem is still not totally fixed. The engine will idle now with no problems as long as the truck isn't in gear. It will also idle fine when in gear and the engine is still cold. However, when the engine warms up and I put the trans in gear, the engine stalls out. Surely this is getting easier to diagnose now that we are narrowing things down. Does anybody have a good idea of what could be causing the engine to die when put in gear after it's warmed up? Thanks to everyone who is chiming in on this. Oh, one other thing. My truck no longer has a catalytic converter. Would installing a new cat help it to run better? I know it would sure stink less. I'm not so sure it runs rich now that I've read up on converters a bit.

[Katrina/10]

It should run fine with or without a catalytic converter. Try swapping the MAP sensor.

[drumdude96]

Well, I'm back to square one again. I tried a new MAP sensor with no success, and once the engine was warmed up, it didn't want to idle at all again. Even with the new EGR and solenoid, it still won't idle. I'm wondering if either the fuel pump is too weak in its old age, or maybe the distributor is defective. Any thoughts guys? This really stinks! BTW, it ran beautifully again until the engine was warmed up.

[pontgta]

Originally Posted by drumdude96

Well, I'm back to square one again. I tried a new MAP sensor with no success, and once the engine was warmed up, it didn't want to idle at all again. Even with the new EGR and solenoid, it still won't idle. I'm wondering if either the fuel pump is too weak in its old age, or maybe the distributor is defective. Any thoughts guys? This really stinks! BTW, it ran beautifully again until the engine was warmed up.

If the steps above did not work. It might be electrical like ignition module.
Bad/weak fuel pump would run rough when you accelerate or highway speeds and probably run fine at idle. I think the only thing that controls idle is the IAC. Does it idle with the IAC disconnected?