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Chevy S10 low idle

13893 Views 4 Replies 3 Participants Last post by  NssJ
2003 GMC Sonoma, 4.3L v6 vin X, 2wd, auto. 100,400mi.

Truck idles at 600rpm. Idles at 1000 until the temp gauge starts to move, then drops to 600. Idle jumps for a sec with A/C switch, but goes right back to 600. Power steering doesn't seem to affect it either. Truck drives at 1600rpm and feels like its in 3rd and OD is off. No Check engine light, no codes.

Not getting much help at S10forum, so figured I'd ask here too.

While doing another unrelated repair, broke GM's cheap plastic distributor housing and had to order a new one. While I was in there, finished rest of tune up stuff. Truck just got new distributor, cap, rotor, plugs, wires, pcv valve, fuel filter. Replaced several dry rotted vacuum lines, clean air filter. Somewhere in all of this, the problem occurred.

Distributor hold down is not adjustable on these. When I installed it, it was close, but not on the line I'd made with the old rotor. I moved it forward one tooth, way off. Back one tooth, close again, back one more tooth, way off. So, I'm pretty sure its installed correctly, though can't exact match previous marks. Was told it may need cam/crank relearn after distributor changes.

I cleaned IAC and throttle, no change. Spray checked all vacuum lines for leaks, no more leaks found.

Took it to mechanic today, "Timing was off 3 degrees, scan tool relearn set back to zero"
Runs slightly better, around 1300rpm at constant speed, but still idles at 600, and still feels like O/D is off.
Mechanic said, I might want to bore out the hold down clamp so I can adjust distributor. I'd rather find a less ghetto solution first if there is one than me custom fabbing parts.

Any suggestions welcome. Thanks!
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· Registered
6,110 Posts
I'm not too sure, as I'm not a mechanic, but you may need to replace the coolant temperature sensor. When those things go whacky, you can have all kinds of strange things happen to that 4.3. If you have a Haynes manual, somewhere in there should be a way to test it for the correct resistance. You'll just need to check the ohms on it, I think.

· Super Moderator
1966 Crown Coupe, 2016 200 S AWD, 1962 Lark Daytona V8.
17,324 Posts
I agree with not tampering with the distributor adjustment. If the timing sync was zeroed with a scan tool, it is now correct and is not the problem.
If the problem started after the tune-up, revisit the tune-up parts and procedures.
Non-OEM parts can be a headache. I always use AC-Delco/Delphi parts on GM vehicles as I would always use Motorcraft parts on Fords. You don't need to buy them at a dealer as many parts stores carry them.
Double-check the vacuum hose routing as pictured on your underhood emissions label.
Sometimes if the ECM can set a fault code for the problem, it will but it might take some time (like a couple of drive cycles until the fault code matures).

· Registered
115 Posts
Discussion Starter · #4 ·
Cleaned MAF and intake air temp sensor.

Idles around 700 now. RPM's still seem high driving, but lower than before. No longer feels like I'm driving in 3rd with O/D off though.
Not great, but no longer horrible either.

I'm trying to sell it, and once it sells, I'm moving. If I planned on keeping it, I could justify AC Delco parts, but hard to toss money into something I know I'm not keeping any longer than I have to. It was over $150 difference for the ACD Distributor, and the cheaper one was smart enough not to make the base out of plastic. I didn't wanna spend more and break the new one also with their torx bit distributor cap bolts. Torx bits into plastic, could they have engineered it any worse? The whole reason I'm where I'm at was removing distributor cap to reach an oil pressure sensor that blew out. Everything broke from there...
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