Not another idle problem !!

[LoDaddo]

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Hi OBS lovers. We're looking at a 92 C1500 with 476K original miles. I've given up on the shotgun approach mechanics and though I'm not much of a wrencher realize that I'm gonna have to take charge of keeping my trucks alive.

About 6 months ago I developed a random high idle that appeared to be temperature related. Lived with it for a while as it wasn't evident on warm days but did continue to become more random/unpredictable. Until recently you could occasionally, but not regularly, shut the truck down and restart after less than a minute and idle would be normal. To date only the manifold temp sensor has been replaced. In regard to this problem.

At the current time, I let the truck warm up and idle drops to almost normal but still a little higher than when it was happy. Most of the time when I put it in gear the idle jumps up (900 +/-). On the occasion that it doesn't increase by putting it in gear, as soon as I give it any throttle it increases and stays. Many of the components were replaced in a previous shotgun attack but, of course, anything is suspect at this time. Gonna have to start by chasing the threads here for a scan tool, but am initially wondering what the relationship is between the tranny and idle as putting it in gear is clearly a triggering event.

Thank you in advance for the advice to come.

 

[scott2093]

88-98 Service Manuals

Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...

www.gmt400.com

X9236 probably has some tests you can work through

 

[Caman96]

Have you tried a TPS sensor?

 

[Schurkey]

Don't "try" parts. Get the scan tool, do the real diagnosis.

Don't forget to verify fuel pressure at prime and under load, inspect for vacuum leaks, and assure that all the usual "tune-up" parts and procedures are within acceptable limits.

I'd pay special attention to the IAC system.

 

[LoDaddo]

Shopping for a scan tool. MT 2500 best choice? I have the 92 in question

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and this 93 yard find I am trying to get on the road. Last registered in 2013 and started on its own. Just would like to know what to look for in the scan tool since, though I can do mechanic stuff, I am not much of a mechanic (yet). Interestingly over the last few days the idle has behaved normally a few times on the 92 which I am thinking must be related to my increased ambient air temperature. Prefer working on stuff with carbs and without computers.

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[Schurkey]

Shopping for a scan tool. MT 2500 best choice?

Acceptable, enormously better than nothing. NOT a "best" choice. They have zero graphing capability, and graphing the sensor signals has become quite important/useful/handy. The newest software available is from 2009, probably covering 2008 vehicles and older. MOST MT2500s will come with software older than that; and you'll want at least two primary cartridges--'81 1/2--'99, and '96--new as you can get, likely 2006. The "Troubleshooter" cartridges are handy but not essential.

I have used an MT2500, I used an MTG2500 for about twenty years. The MTG has two-channel graphing although it's very crude.

When my MTG died, I moved up to a Solus Pro: 1 to 4 channel graphing with far better resolution, heaps of memory for previous vehicles (time saver) and just generally faster/more powerful/leaps tall buildings in a single bound, etc.

Yummy. What hull is that? I don't remember seeing one with the lil' windshield in front of the driver. I blew-up the photo, but there's not a lot of resolution. I think I'm seeing a hint of cavitation plate, and the distributor is forward, so I'm guessing V-drive with BBC.

 

[LoDaddo]

Great, thanks for that info. See what I can find. Gonna check with a couple mechanics I know, see if maybe they have something laying around they don't use any more. Mostly just wanting to keep my OBS trucks alive. Simple enough I should be able to self diagnose once I have the right equipment. A box full of parts and some sweat equity will leave me way ahead compared to the cost of a new anything .

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V-drive she is. 1975 Hondo t-deck runner bottom. Merlin II block, Brodix heads, old school Edelbrock tunnel ram with 660s, pump gas.
Originally came with a plexiglass "windshield". Fabbed that one out of aluminum so I could have it powder coated.

 

[LoDaddo]

Here's a lead in to another question. Not too many years ago I had to replace my EGR. Got it from Chevrolet and it came out of the Delco box "Made in China". Are they maintaining quality control at a higher level than the aftermarket folks to make it worth the extra cost?

 

[Schurkey]

Here's a lead in to another question. Not too many years ago I had to replace my EGR. Got it from Chevrolet and it came out of the Delco box "Made in China". Are they maintaining quality control at a higher level than the aftermarket folks to make it worth the extra cost?

No, not really. "OEM quality" isn't really OEM quality any more. OTOH, some aftermarket crap is so terrible that the cost-cut, offshored junk in a GM box is still better than the aftermarket stuff. It's a race to the bottom.

I had the same situation with a driver's outside mirror on my '92 Lumina. The 11-year-old Made-In-Canada mirror was still in a shiny-black housing, had some stone chips. the "new" Made-In-China mirror that came from the dealership in an unopened box was dull light-grey in six months. Total junk.

 

[df2x4]

With a lot of research (and a bit of luck) sometimes you can figure out who's supplying GM/ACDelco for certain parts. With that knowledge you can buy straight from the source and save some money. Not always possible, but if you compare photos and details sometimes it's fairly obvious.