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Chevy S10 Has Rough Idle Problem

Q. I have a 1994 Chevy S10 Extended cab 2WD, with a TBI 4.3, with A/C and P/S. This truck had 40,000 miles on it when I purchased it in 1998. From the day I got it it had a slightly rough idle, and a small surge at about 1,500 to 1,900 RPM. It has gotten worse over the years, I currently have 117,000 miles on it now, to the point that it is a 400 RPM surge at 1,900 RPM.

Chevy S10 Has Rough Idle Problem

The power is gone to the point that on the freeway with the A/C on I have to down shift from OD to third any time I get below 60 MPH.

Here in Dallas TX, we have to pass a smog test yearly, it has always passed with flying colors, but the Oxygen seams to me to be too low. The hydrocarbons have always been very low also, but when i leave it idling it always smells rich like an old carbureted big block.

I have replaced the EGR valve, EGR controller, MAP sensor, plugs, cap and wires, twice, and the plastic vacuum harness. I am at a loss what else to do. I have been thinking of trying a MSD ignition and coil, and a chip, but do not want to spend anymore than is necessary to get back the impressive power and drivability that was there when I bought it.

Thank you very much for your time.
Hurst, TX

A. You need to check some basics. How's the fuel pressure? Have you changed the fuel filter? Check to make sure timing is set properly? Plugs gapped to spec? After all these, I would get it scanned while driving to see if they can locate any problems under load.

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