Stalling and running rough when hot

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So I recently bought a 1991 Vanagon GL 4 speed. It starts great, but after running it for a while, it starts running rough, and eventually starts to stall unless I feather the throttle. Also, all 4 spark plugs are extremely sooty.

I am at a loss as to where to start troubleshooting, but I replaced the spark plug wires and spark plugs, air filter, distributor cap and rotor are almost new.

Can someone give me a few hints as to what might be cause either or both of these issues? I am mechanically inclined, so that is thankfully not an impediment!

Thanks in advance!

sERGE

[Pchill2]

I would first take a look at the distributor cap. It’s new but it still could have a crack in it. When the engine heats up the crack gap opens up which causes the engine to run rough.

If that looks good I would throw an O2 sensor at it and see if that helps. On startup the ECU uses tabulated fuel and ignition values until coolant temps warm up at which point it switches to O2 sensor data to determine AFR. A faulty O2 sensor will cause the engine to do what you describe.
_________________
87 Syncro Westy
Honda K24 swap

[4Gears4Tires]

Coolant temp sensor, fuel pressure regulator, injectors, fuel pump, fuel filter, and ecu are all things you can replace at one go if you want to try the parts shotgun approach. Probably should do the regulator, pump, and filter anyway if you just got it, even if it was running smoothly.
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'87 Syncro
Ferric Oxyhydroxide Superleggera Edition

[thatbaldwinlife]

I would start with testing the Temp II sensor as outlined in the Bentley. Then move on to the O2 sensor testing. It should all be outlined on this forum as well.
Good luck!
nate
_________________
1987 Westy
Insta: @Thatbaldwinlife
Vanagon Adventure and DIY videos:
That Baldwin Life YouTube Channel

[Wildthings]

You should test the coax for the O2 sensor to make sure the signal lead (center wire) is not shorted out to ground.

[michaelasnider]

http://oldbluesblog.com/files/DigifantProTrainingManual_SingleSided.pdf

This is the best place to start with some troubleshooting. See: 'Poor Performance - At Operating Temperature'

- Basic Engine Adjustments
- Throttle Switch
- Oxygen Sensor System
- Ignition System
- Fuel System
- Idle Stabilization System


All the recommendations above from others are captured in here, but this will give you methodical approach and you basically just need a multimeter, a test light, and a jar.

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So now that I bought 4 new fuel injectors, but have not installed them, the van has STOPPED stalling! Don't ask me why, but I ran it for about an hour driving in highway and around town, and it never even sputtered once. I am going to pull the plugs and clean them this weekend, remove the old fouling, and see if its running any cleaner. I have a suspicion:
I *think* it may have had too much oil?! I changed the oil and tranny fluid the second I got the van, and if memory serves me, I think I put in 4.5 quarts? I put in what the Bentley said I needed.

Anyway, I noticed I am running about a half quart low (if the dipstick is to be believed!) and now miraculously its running and not stalling.

I have done a few things though . . . I added 16 oz of Seafoam to the gas about 2 weeks ago and refilled with regular (87 octane). I also added 6 oz to the motor oil just to clean out any gunk in the crankcase. Yes I know that the gunk is what keeps that engine from bleeding itself dry, but I was desperate!

I am going to do an oil change this weekend if I can find a good oil filter. I'll see if O'Reilly's can order one and get it to me quick. As a lot of folks have seen on their own vans, the oil light blinks ocassionally on my van too, so I am thinking I may just change all the O2 sensors and pressure monitors anyway.
If I start to experience the stalling again, I will update!

As always, THANK YOU ALL FOR THE KNOWLEDGE YOU SHARE!! Seriously, THANK YOU!