Zeeyalater

Hello everyone I am new here but I am also confident that my problem isn't. I have a 1982 s-130 non-tubo. Long story short, not too long ago my car started stumbling and hesitant to accelerate. I notice that it start happening after 15-20 of driving (doesn't happen at start up). within 15-20 of driving the car start stumbling and it doesn't want to go. If I try to force it (pedal to the medal) after a minute or two the car doesn't want to go at all. There is also a popping coming from the exhaust system. HOWEVER, if I turn the car OFF and back ON right away it drives normal until another 15-20 minutes then it stumbles and act up again. Here is what I done so far:

Spark plugs and wires are relatively new
Inspected vacuum line and they all look good.
Swapped TPS with brand new one - Nogo
Swapped Idle Air Control Valve with new one - Nogo
Cleaned and adjusted AFM. I turned the gears anti-clockwise (at the most 8 teeth) and clockwise (at the 4 teeth). I'm not sure what's the most I can turn it to the clockwise (strengthening), which leans it out because I read something on the forum that said leaning it under manufactured spec can ruin your engine and I'm not sure what the manuf specs are.

I am pretty much stumped and don't know what else to do.......?

NismoPick

Welcome to ZDriver!

Sounds like you've already dug pretty deep. Next you should check the CHTS (cylinder head temp sensor). Check the connection & do an ohm test. Download the FSM for free at XenonS130 - S130 Reference

FricFrac

Check for vacuum leaks not just a visual inspection.

Zeeyalater

NismoPick: Thanks for the insight. I just ordered a new CHTS that should be here tmrw.

FricFrac: If CHTS doesn't resolved I guess I will do another vacuum evaluation. Btw, other then visual inspection whats another efficient and effective way to inspect vacuum?

Btw, I read a post in this forum where a guy stated that he had the same issue and he resolved the issue by tightening (strengthening) the spring on the AFM. He also mention that the more he tighten the spring the better his car ran. I also read on here ("http://www.kamikazeracing.org/dl/JsAFMRebuild/") it stated that (NOTE: DO NOT, under any circumstance lean your mixture out below the factory setting unless you have an air/fuel mixture meter hooked up. This can cause serious engine damage. A rich mixture will do nothing more than cause driveability issues and maybe foul your plugs. A lean condition can destroy your engine.) My question is does anyone know what the specs are? I want to try tightening the spring on the AFM but unsure whats the most I can turn the wheel (as in how many teeth.) The most I done was 4 teeth. I was skeptical. I didn't know if that was over or under spec.

Zeeyalater

NismoPick: I just ordered a new CHTS and should be here tomorrow

FricFrac: If CHTS does not work I will do another vacuum inspection. Btw, whats another method to inspect vacuum more effective and efficient other then visually inspecting?

Here a question I have guys: I read on this forum (https://www.zdriver.com/forums/280zx...se-help-34068/) with a guy that had the same issue and he stated he resolved it by tightening (strengthening) the spring on the AFM which leans it out. He also mention that the more he tighten the spring the better his car ran. However, while I was doing some research I came across this information on this page (http://www.kamikazeracing.org/dl/JsAFMRebuild/) it stated (NOTE: DO NOT, under any circumstance lean your mixture out below the factory setting unless you have an air/fuel mixture meter hooked up. This can cause serious engine damage. A rich mixture will do nothing more than cause driveability issues and maybe foul your plugs. A lean condition can destroy your engine.) Now with that being said, does anyone now the spec of factory setting? I did tighten my spring on the AFM but did not gone beyond 4 teeth. I don't know if the 4 teeth was under or over spec. I do want to try and tighten it more but am skeptical due to engine damage. What do you guys think of me going beyond the 4 teeth and tightening (leaning it out) the spring even more?

FricFrac

If you want to tune your car you need an aftermarket ECU. You can only tweek the car in a minor hackish kind of way with the AFM - it's pretty primative. Get it running properly with the stock setup before you start playing...

Zeeyalater

Here's the update guys:

Okay, here's the update since we last spoken. So I gotten the chance to replaced the CHTS anad AFM with all new ones.

CHTS: Nothing changed.

AFM: I notice that with the new AFM the idle seems a little rough like the car was running leaner.

All said and done I was hoping with the new parts it would resolved the issue however after I took the car for a test drive after 15-20 minutes the problem came back. i did a re-inspection with the vacuum. This time I let the car ran and sprayed carb cleaner on all the vacuum but could not a leak. I know my problems common but what seem unique about to me is that when the problem occurs I can restart the car right away and the problems goes away like nothing was ever wrong with it. I am still scratching my head and wondering what can it be however after replacing these part I gotten to narrow the list down. Any suggestion guys?

FricFrac

Bad connection somewhere or the ECU is intermittant?