92 suburban having idle issues.

[AyWoSch Motors]

My 92 GMC suburban is having issues at idle. It just started yesterday when I went to start it to move it. Didnt want to start, unless I gave it a little bit of pedal input. Then when it did start, I wanted to idle at 500rpm or less. Stalled out a few times. But finally got it to idle at around 6-700 ish. Then I took it out for a ride around and it runs and drives fine. Everytime I let off the gas though, it wants to idle down immediately. Then I got back and parked it and shut it off. Then I started it back up to see if it would do it again, and then it was idling between 1500 and 2k and wont come down. So I shut it off and started it again, and it did it again at high idle.
Doesn't seem to have a happy medium right now.
Other wise the engine is running well. Sounds smooth, throttle is snappy, no stumbling. Just idles to low or too high.

Any thoughts?

 

[Schurkey]

What is the fuel pressure? Does the fuel pump prime?

Connect a scan tool, look at all the sensors, but especially TPS, and Coolant Temp sensor. Also, verify computer outputs especially IAC and spark advance. Does the RPM showing on the scan tool match the dash tach?

Vacuum leaks at the throttle-body base gasket seem to be common.

 

[AyWoSch Motors]

What is the fuel pressure? Does the fuel pump prime?

Connect a scan tool, look at all the sensors, but especially TPS, and Coolant Temp sensor. Also, verify computer outputs especially IAC and spark advance. Does the RPM showing on the scan tool match the dash tach?

Vacuum leaks at the throttle-body base gasket seem to be common.

I don't have a scanner tool for OBD1.

Temp sensor or TPS sounds about right. I can go check what fault codes I have with a paper clip.

 

[Schurkey]

I don't have a scanner tool for OBD1.

Maybe it's time to get one. You've posted about two different Suburbans that don't run right--a '92 and a '98. You wouldn't even need a scan tool with new/recent software.

It'd save you a heap of work, and lots of time. Blinky-lights are better than nothing, but they're no match for actual data direct from the sensors, plus fuel trims, and some bi-directional control.

 

[AyWoSch Motors]

Maybe it's time to get one. You've posted about two different Suburbans that don't run right--a '92 and a '98. You wouldn't even need a scan tool with new/recent software.

It'd save you a heap of work, and lots of time. Blinky-lights are better than nothing, but they're no match for actual data direct from the sensors, plus fuel trims, and some bi-directional control.

Not a bad idea. I'll see if I can order one. I asked about one at my local parts store a while back, but they dont sell them.

I have a OBD2 scanner. But it doesn't tell me anything more than the paperclip, just eliminates the step of looking up what the trouble code means.


"Software". That little word right there, that's the issue, haha. In my personal opinion, i like cars better before computers, although many will disagree with me I'm sure.

 

[AyWoSch Motors]

This is my current one. Could I possibly just get an adapter for it, to go from OBD1 to OBD2 so I could still use this one?

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[Schurkey]

I don't know the Actron line. I'll take a guess: That unit will not be compatible with OBD 1.

Does it even provide live data for OBD-2? Looks like a code-reader, not a scan tool.

When it was me, I bought used, professional-grade tools from eBay rather than "inexpensive" new tools.

 

[AyWoSch Motors]

I don't know the Actron line. I'll take a guess: That unit will not be compatible with OBD 1.

Does it even provide live data for OBD-2? Looks like a code-reader, not a scan tool.

When it was me, I bought used, professional-grade tools from eBay rather than "inexpensive" new tools.

That one is only for OBD2, was given to me buy someone that didnt need it anymore. Its come in handy a few times, but that's why I was wondering if theres an adapter I could use to make it work in older ones.
It says "Auto Scanner" on it, but its only function as far as I can tell is to read codes. Doesnt do anything else.
But are the OBD1 and 2 era ports/ecm capable of telling you anymore than that? I know the computers in new cars do everything but take out the trash, but I figured the ecm in a 92 is only capable of spitting out a DTC and that's it.
If a newer fancier diagnostic scanner would actually come in handy on something this old, I will spend the money to invest in a nice one, but otherwise I dont see the point.

 

[df2x4]

But are the OBD1 and 2 era ports/ecm capable of telling you anymore than that?

Yes, absolutely. OBD1 and 2 are both capable of live sensor data output and lots of other cool stuff. You just need a capable scan tool.

As Schurkey mentioned, you don't necessarily need a fancy new scan tool. I bought a Chinese clone of a GM Tech 2, which was the diagnostic tool used at GM dealerships when these trucks were new (and the tool that the GM factory service manuals were written around). They've been replaced by newer tools now so they won't work with brand new vehicles, but they'll do anything GM from 1991-2013. Unfortunately the Chinese Tech 2 clones are getting tough to find at reasonable prices, and authentic Tech 2s can be over $1K (and very difficult to distinguish from the clones). I'm sure others can give you some good advice on other high quality older scan tools to look out for though. IIRC Snap-On has some nice older models that you can find used for a few hundred bucks.

 

[Schurkey]

But are the OBD1 and 2 era ports/ecm capable of telling you anymore than that? I know the computers in new cars do everything but take out the trash, but I figured the ecm in a 92 is only capable of spitting out a DTC and that's it.
If a newer fancier diagnostic scanner would actually come in handy on something this old, I will spend the money to invest in a nice one, but otherwise I dont see the point.

www.gmt400.com/threads/91-suburban-still-dead-in-the-water-no-pulse-at-injectors.58190/page-2#post-1242757

91 suburban still Dead in the water no pulse at injectors

Keep in mind guy's, this is an OBD1 ECM, and any codes can be pulled with a paper clip. Since I haven't had an OBD1 system in well over 10 years, I'm not sure what kind of system readers are available for this system. Is there a live date reader for OBD1? Where you at @PlayingWithTBI

www.gmt400.com

Click on the link to the outside forum for photos and description of what an ancient "real" scan tool can do on OBD 1.