Another rough idle thread

[tsr2185]

My truck idles rough when hot. Starts up and idles fine and drives fine. Noticed when ac or defrost is on (compressor unplugged cause low on froen) it idles better. Thoughts? 91 350 tbi.
Replaced within last 6 months:
IAC
plugs and wires
Distributor
Coil
Egr
Temp sensor
All vac lines, plugged off EVAP
PCV and hose

 

[Schurkey]

Verify fuel pressure.

Connect a scan tool, look at the data stream. Make sure all the sensor data makes sense, make sure all the outputs are working appropriately.

WHY would you "plug off EVAP"?

 

[tsr2185]

Verify fuel pressure.

Connect a scan tool, look at the data stream. Make sure all the sensor data makes sense, make sure all the outputs are working appropriately.

WHY would you "plug off EVAP"?

Canister and vac lines are in rough shape. So I plugged the evap vac port on the TBI. Also, I noticed it runs better when I unplug the IAC. I would assuming it dumping fuel means that it maybe just starving for fuel. My next step should be verify fuel pressure like you said. Gotta order a port to test it with. Any suggestions?

 

[Schurkey]

Plugging the "Evap" likely means your fuel tank isn't venting. That's not a good thing.

Make sure the Schrader valve on your fuel pressure testing adapter is the same size/thread as the fitting on your fuel pressure gauge.

I ordered a TBI adapter; discovered when it showed up that my pressure gauge wouldn't connect to it. Had to order a packet of ten Schrader valve assemblies, to get some that would actually work.

 

[tsr2185]

Plugging the "Evap" likely means your fuel tank isn't venting. That's not a good thing.

Make sure the Schrader valve on your fuel pressure testing adapter is the same size/thread as the fitting on your fuel pressure gauge.

I ordered a TBI adapter; discovered when it showed up that my pressure gauge wouldn't connect to it. Had to order a packet of ten Schrader valve assemblies, to get some that would actually work.

I didnt plug the evap canister, it vents to the engine bay. Havent had a problem with odor either (I fill up maybe once a month).

Looking at a 3way with a inline guage when I order one. Like 60$ for the pair.

 

[thinger2]

Not too long ago, I was all about dianosing TBI with a voltmeter and a vacuum gauge.
And that worked for years because we could buy good parts.
It was easy as ****.
I always took a big mechanical turd on people who needed "Data"
And Im am a dope.
Parts are junk.
You cant bolt em in without ******* up the source of that dats.
And the parts are junk.
Schurkey is right, get some live data.
Dont listen to me.
Im gonna move on to BBQ salmon and then you all got no hope