87 R20 5.7L Dying when Idling

[Raffles]

Hey everyone. My wife bought her granddad's 87 R20, and I'm trying to get it back to being reliable. Tackling one problem at a time, I started with the engine idle. When you start it up (and it can take a couple tries) it'll idle fine. When you shift to drive, the RPM will dip significantly, but she'll usually stay running. Driving is fine - no issues there. When you come to a stop, though, she'll die again, though you can restart her immediately.

I've gone through a few things so far:

• Replaced fuel filter
• Replaced fuel pump
• Replaced plugs
• Replaced air filter
• Cleaned TB
• Checked/de-nastied PCV

I've noticed there are definitely some bits missing under the hood:

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Engine compartment. Notice the jack held on with a bungee? Basically sets the tone for this whole mess.

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Intake snorkel is rotted beyond repair. Anyone got a part number? Also, missing heat stack and the hose to the left of the intake port (not sure where that goes).

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Diverter valve. Pretty sure there should be hoses on those two ports...

So like I said, I know I have a long way to go with this thing. If anyone can offer some advice, I'd greatly appreciate it.

 

[4WDKC]

replaced the battery recently?

 

[Raffles]

replaced the battery recently?

Yup, battery's probably six months old.

 

[4WDKC]

there is an IAC relearn/calibration that probably needs to be done.

 

[Colin]

What rpm does it idle at?
I'm thinking the PCV valve should be on the other side and a tube from the air cleaner
should plug into the port its currently occupying.

 

[RetroC10Sport]

Check vacuum and fuel pressure are two things.

Check engine light on?

 

[1987 GMC Jimmy]

I'd continue the vacuum leak journey since you started with the PCV. If you didn't replace the base gasket when you had the TB off, I'd do that. I'd do a visual inspection of everything that your emissions sticker says plus the port that's at the back of the intake that A/C mode control and cruise use. I'd make sure the brake booster isn't causing your problems, either. Fuel pressure is a good idea, too. The IACV relearn is jump the two top right hand pins on the ALDL with a paperclip, turn they key on, leave it for thirty seconds, unplug the IAC connector, turn the key off, and remove the jumper. It's important to note if the SES light is coming on when problems arise and if it comes on at all when you first get ready to start it up and turn the key to ON. I'd finish the ignition tune up. It's a good idea to replace the wires if they look old or if the connectors look anything but shiny. The cap and rotor are cheap parts that should be replaced with the plugs. Use all AC Delco ignition parts. If it sat for a long time, it'd be a good idea to get all the bad fuel ran out of there and rebuild the TBI because of what ethanol tends to do over time.

 

[Raffles]

What rpm does it idle at?
I'm thinking the PCV valve should be on the other side and a tube from the air cleaner
should plug into the port its currently occupying.

Went to go check. Just realized this thing doesn't even have a tach, FFS.

There's a tube from the air cleaner on the driver's side aft end, and the PCV's sitting on the foreward end of the passenger side.

Check vacuum and fuel pressure are two things.

Check engine light on?

No CEL, but I'd actually be surprised if her granddad hadn't cut the wires to it.

I'd continue the vacuum leak journey since you started with the PCV. If you didn't replace the base gasket when you had the TB off, I'd do that. I'd do a visual inspection of everything that your emissions sticker says plus the port that's at the back of the intake that A/C mode control and cruise use. I'd make sure the brake booster isn't causing your problems, either. Fuel pressure is a good idea, too. The IACV relearn is jump the two top right hand pins on the ALDL with a paperclip, turn they key on, leave it for thirty seconds, unplug the IAC connector, turn the key off, and remove the jumper. It's important to note if the SES light is coming on when problems arise and if it comes on at all when you first get ready to start it up and turn the key to ON. I'd finish the ignition tune up. It's a good idea to replace the wires if they look old or if the connectors look anything but shiny. The cap and rotor are cheap parts that should be replaced with the plugs. Use all AC Delco ignition parts. If it sat for a long time, it'd be a good idea to get all the bad fuel ran out of there and rebuild the TBI because of what ethanol tends to do over time.

I'm gonna soap the lines tomorrow and see if I can find anything. I'll also try the IACV relearn while I'm out there. Once I evicted the raccoons from the engine bay, I didn't see anything potentially deal-breaking - hoses are generally in good condition, if a bit nasty. Plugs are brand new. Plug wires look fairly new, but I don't know if they've been done yet. She was driven down to Austin from Dallas, so the tanks have been run through a couple times. I may bite the bullet and get the TB rebuild kit. We'll see if anything turns up tomorrow.

 

[1987 GMC Jimmy]

If anything related to the engine management system was clipped, that’s a problem. If the ECM is working correctly, though, it should tell you if that’s happened. I don’t think soaping is gonna tell you much since the force at hand is sucking and not blowing (haha, very funny). You can use any number of combustible aerosols or propane from a little torch to see if it sucks it in and changes the idle speed. A vacuum gauge would help you determine how close or far away you are from nominal vacuum. You can also disconnect lines at their vac source and blow smoke in them from say a cigar and see if any wafts out from somewhere. You can also pinch soft lines or plug them while using a gauge to see if any changes occur. There are a ton of ways, and all of them work.

 

[RetroC10Sport]

Maybe in a weekend or two, Abby, Bertha the C30 and I can take a ride to Hutto with my computer, ALDL cable and diagnostic knowledge to help out if you're available.

 

[foamypirate]

You could always do what I did when my 88' R20 wouldn't idle or run right...

I yanked the 350 and put a 6.0L LS and and NV4500 manual trans in it, lol.

In any case, these guys will help you get on the right track. I'm afraid my TBI troubleshooting skills are a bit rusty these days, so I'm not much actual help beyond what has already been mentioned. I'm certainly happy to be the peanut gallery, however!

 

[HotRodPC]

If it's not been mentioned yet, check the EGR Valve. It's not all that hard to remove it and clean it. Sometimes you get a piece of carbon hung up in there and it won't close off all the way at idle then you've got an internal vac leak.

 

[1987 GMC Jimmy]

Maybe in a weekend or two, Abby, Bertha the C30 and I can take a ride to Hutto with my computer, ALDL cable and diagnostic knowledge to help out if you're available.

You’re more than welcome to swing by ole 39191 when you get done there and give me a hand with the GMC. Good help is slim pickings. And by that I mean nonexistent.

 

[Raffles]

Maybe in a weekend or two, Abby, Bertha the C30 and I can take a ride to Hutto with my computer, ALDL cable and diagnostic knowledge to help out if you're available.

I'd dance at your wedding if you did. Alternately, I have beer and some other foreign alcohol.

 

[Raffles]

If it's not been mentioned yet, check the EGR Valve. It's not all that hard to remove it and clean it. Sometimes you get a piece of carbon hung up in there and it won't close off all the way at idle then you've got an internal vac leak.

Yeah, I was looking at taking that off today.

As an aside, can anyone tell me what some of these missing hoses would go to (like that last photo)?